How COVID-19 causes neurological damage

Authors: Date:nnNovember 14, 2022 University of Basel

Summary:It’s not uncommon for people to lose their sense of taste and smell due to a COVID-19 infection. In others, the disease has had an even stronger impact on the nervous system, with effects ranging from lasting concentration problems to strokes. Now, researchers have reported new insights into the development of ‘neuro-COVID’.

It’s not uncommon for people to lose their sense of taste and smell due to a Covid-19 infection. In others, the disease has had an even stronger impact on the nervous system, with effects ranging from lasting concentration problems to strokes. Now, researchers led by Professor Gregor Hutter from the Department of Biomedicine at the University of Basel and University Hospital of Basel have reported new insights into the development of “neuro-Covid” in the journal Nature Communications.

Specifically, the team investigated how different severities of neuro-COVID can be detected and predicted by analyzing the cerebrospinal fluid and blood plasma of affected individuals. Their findings also offer some indications of how to prevent neurological damage due to Covid-19.

The study included 40 Covid-19 patients with differing degrees of neurological symptoms. In order to identify typical changes associated with neuro-Covid, the team of researchers compared these individuals’ cerebrospinal fluid and blood plasma with samples from a control group. They also measured the brain structures of test subjects and surveyed participants 13 months after their illness in order to identify any lasting symptoms.

Holes in the blood-brain barrier

Particularly in the group with the most serious neurological symptoms, the researchers identified a link with an excessive immune response. On the one hand, affected individuals showed indications of impairment of the blood-brain barrier, which the study’s authors speculate was probably triggered by a “cytokine storm” — a massive release of pro-inflammatory factors in response to the virus.

On the other hand, the researchers also found antibodies that targeted parts of the body’s own cells — in other words, signs of an autoimmune reaction — as a result of the excessive immune response. “We suspect that these antibodies cross the porous blood-brain barrier into the brain, where they cause damage,” explains Hutter. They also identified excessive activation of the immune cells specifically responsible for the brain — the microglia.

Blood test as a long-term objective

In a further step, Hutter and his team investigated whether the severity of neurological symptoms is also perceptible in brain structures. Indeed, they found that people with serious neuro-Covid symptoms had a lower brain volume than healthy participants at specific locations in the brain and particularly at the olfactory cortex — that is, the area of the brain responsible for smell.

“We were able to link the signature of certain molecules in the blood and cerebrospinal fluid to an overwhelming immune response in the brain and reduced brain volume in certain areas, as well as neurological symptoms,” says Hutter, adding that it is now important to examine these biomarkers in a greater number of participants. The aim would be to develop a blood test that can already predict serious cases, including neuro-Covid and long Covid, at the start of an infection.

Targets for preventing consequential damage

These same biomarkers point to potential targets for drugs aimed at preventing consequential damage due to a Covid-19 infection. One of the biomarkers identified in blood, the factor MCP-3, plays a key role in the excessive immune response, and Hutter believes there is the potential to inhibit this factor medicinally.

“In our study, we show how coronavirus can affect the brain,” he says. “The virus triggers such a strong inflammatory response in the body that it spills over to the central nervous system. This can disrupt the cellular integrity of the brain.” Accordingly, Hutter says that the primary objective must be to identify and halt the excessive immune response at an early stage.

Journal Reference:

  1. Manina M. Etter, Tomás A. Martins, Laila Kulsvehagen, Elisabeth Pössnecker, Wandrille Duchemin, Sabrina Hogan, Gretel Sanabria-Diaz, Jannis Müller, Alessio Chiappini, Jonathan Rychen, Noëmi Eberhard, Raphael Guzman, Luigi Mariani, Lester Melie-Garcia, Emanuela Keller, Ilijas Jelcic, Hans Pargger, Martin Siegemund, Jens Kuhle, Johanna Oechtering, Caroline Eich, Alexandar Tzankov, Matthias S. Matter, Sarp Uzun, Özgür Yaldizli, Johanna M. Lieb, Marios-Nikos Psychogios, Karoline Leuzinger, Hans H. Hirsch, Cristina Granziera, Anne-Katrin Pröbstel, Gregor Hutter. Severe Neuro-COVID is associated with peripheral immune signatures, autoimmunity and neurodegeneration: a prospective cross-sectional studyNature Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-34068-0

Hypoglossal Nerve Palsy Following COVID-19 Vaccination in a Young Adult Complicated by Various Medicines

Authors: Tatsuhiko OkayasuRyuichi OhtaFumiko YamaneSatoshi AbeChiaki Sano

 September 15, 2022 (see history) DOI: 10.7759/cureus.29212 Cite this article as: Okayasu T, Ohta R, Yamane F, et al. (September 15, 2022) Hypoglossal Nerve Palsy Following COVID-19 Vaccination in a Young Adult Complicated by Various Medicines. Cureus 14(9): e29212. doi:10.7759/cureus.29212

Abstract

Mononeuritis multiplex is a rare form of cerebral nerve palsy caused by various factors. Coronavirus disease 2019 (COVID-19) vaccination could be an etiology of mononeuritis multiplex, which can affect various nerves. Post-COVID-19 and vaccination-related neurological impairments involve cranial nerves such as the facial, trigeminal, and vagal nerves. We report our experience with a 34-year-old man who developed hypoglossal nerve palsy following COVID-19 vaccination, complicated by progressive mononeuritis multiplex. Hypoglossal nerve palsy may occur following COVID-19 vaccination. The symptoms vary and may progress without treatment. Physicians should consider the possibility of mononeuritis multiplex after COVID-19 vaccination and provide prompt treatment for acute symptom progression.

Introduction

Mononeuritis multiplex is a rare form of cerebral nerve palsy caused by various factors, as the etiologies, infection, and autoimmunity are common. Herpes zoster and simplex are the predominant infections in the category of infection [1,2]. Among autoimmune causes, small-to-medium-sized vasculitis, such as an antineutrophil cytoplasmic antibody (ANCA)-related vasculitis and Sjogren’s syndrome, are common [1,2]. The progression of mononeuritis multiplex symptoms varies depending on the human body’s etiology and immunological reactions [3,4]. Severe cases may involve multi-extremity paralysis, which should be treated with intravenous immunoglobulin therapy, steroids, and plasma exchange, according to the etiology [2,5]. Thus, effective treatment requires the detection of etiology and rapid treatment.

COVID-19 and COVID-19 vaccinations are also potential etiologies of mononeuritis multiplex, which can affect various nerves. Based on previous reports, post-COVID-19 and vaccination-related neurological impairments involve cranial nerves such as the facial, trigeminal, and vagus nerves [6-8]. However, there are few reports of mononeuritis multiplex following COVID-19 vaccination. Here, we report a case of mononeuritis multiplex that spread from the right hypoglossal nerve to the right hand and leg. The progression was acute, and the patient required treatment with intravenous immunoglobulin and steroid pulse therapy. Various complications occurred during the clinical course, and the treatment course was complicated. Our case demonstrates the importance of a clinical diagnosis of mononeuritis multiplex with prompt treatment and approaches to reduce long-term complications.

Case Presentation

A 34-year-old man was admitted to our hospital with a chief complaint of dysphasia and difficulty speaking. Ten days before admission, the patient had received the third vaccination for COVID-19. He had a fever of >38 °C one day after vaccination. Seven days before admission, he experienced tingling on the right side of his tongue, followed by dysphagia and difficulty speaking. These symptoms progressed, and the patient noticed that the right side of his tongue had shrunk; therefore, he visited our hospital. He had a past medical history of varicella-zoster virus infection in the first branch of the left trigeminal nerve and had been treated with valaciclovir. The patient did not take any regular medication.

His vital signs at admission were as follows: blood pressure, 114/59 mmHg; pulse rate, 78 beats/min; body temperature, 36.9 °C, respiratory rate, 15 breaths/min; and oxygen saturation, 97% on room air. He was alert to time and place. Physical examination showed that the right half of his tongue was atrophied and shifted to the right during the prostration.

No other abnormal neurological findings were noted. There were no obvious abnormalities in the chest or abdomen and no skin eruptions. Physical examination revealed right hypoglossal nerve palsy; thus, viral infection, brain stroke, brain tumor, meningitis, ANCA-related vasculitis, and Guillain-Barre syndrome was suspected. Blood tests, head magnetic resonance imaging (MRI), head computed tomography (CT), and lumbar puncture were performed. The results were within normal limits (Table 1).

MarkerLevelReference
White blood cells6.83.5–9.1 × 103/μL
Neutrophils5144.0–72.0%
Lymphocytes32.918.0–59.0%
Monocytes80.0–12.0%
Eosinophils6.90.0–10.0%
Basophils1.20.0–3.0%
Red blood cells5.343.76–5.50 × 106/μL
Hemoglobin1611.3–15.2 g/dL
Hematocrit47.833.4–44.9%
Mean corpuscular volume89.579.0–100.0 fl
Platelets24.613.0–36.9 × 104/μL
Total protein6.96.5–8.3 g/dL
Albumin4.43.8–5.3 g/dL
Total bilirubin0.50.2–1.2 mg/dL
Aspartate aminotransferase188–38 IU/L
Alanine aminotransferase274–43 IU/L
Alkaline phosphatase80106–322 U/L
γ-Glutamyl transpeptidase50<48 IU/L
Lactate dehydrogenase165121–245 U/L
Blood urea nitrogen13.98–20 mg/dL
Creatinine0.660.40–1.10 mg/dL
eGFR≥90> 60.0 mL/min/1.73 m2
Serum Na137135–150 mEq/L
Serum K3.93.5–5.3 mEq/L
Serum Cl10198–110 mEq/L
Serum P3.12.7–4.6 mg/dL
Serum Mg21.8–2.3 mg/dL
CK11256–244 U/L
CRP0.07<0.30 mg/dL
Artery blood gas analysis  
pH7.4187.35–7.45 
PCO242.535.0–45.0 mmHg
PO289.375.0–100.0 mmHg
HCO326.920.0–26.0 mmol/L
Lactate1.20.5–1.6 mmol/L
Cerebrospinal fluid testing  
Colorclear 
Cell count10–5 /μL
Protein3615–45 mg/dL
Glucose5748–83 mg/dL
Chloride126.5113–128 mEq/L
Table 1: Initial laboratory data of the patient

eGFR: estimated glomerular filtration rate; CK: creatine kinase; CRP: C-reactive protein

A videoendoscopic examination of swallowing was performed to evaluate dysphagia, with no obvious problems associated with swallowing function. Since the difficulty in moving the tongue and the white coating was remarkable, the patient was referred to a dental and oral surgeon to rule out tongue cancer.

Because the patient had a history of herpes zoster, we also considered viral reactivation and prescribed acyclovir (1500 mg/day) and prednisolone (60 mg/day) from the second day of admission. However, lumbar pain and headache appeared on day four of admission, for which epidural hematoma after lumbar puncture was suspected. Plain lumbar magnetic MRI and head CT showed edematous findings around both kidneys, clinically suggesting the possibility of acute kidney injury due to acyclovir. As the patient tested negative for varicella virus, acyclovir was discontinued (Figure 2).

Edematous-findings-around-both-kidneys-(blue-arrows)
Figure 2: Edematous findings around both kidneys (blue arrows)

On the seventh day of illness, weakness of the right upper and lower extremities and a Romberg’s sign was observed. Plain MRI of the upper arm and nerve conduction velocity tests were performed to investigate the cause, with no positive findings. Blood tests were negative for syphilis, hepatitis, HIV, ANCA, antinuclear antibody, and IgG4. Therefore, a clinical diagnosis of mononeuritis multiplex after administering the COVID-19 vaccine was made. On day seven of admission, prednisolone (60 mg/day), intravenous immunoglobulin (0.4 g/kg/day for five days), and methylprednisolone (1 g/day for three days) were initiated after consultation with a neurology physician. On day nine of admission, muscle pain, and general malaise developed immediately after intravenous methylprednisolone administration. As intravenous methylprednisolone could be the cause, the administration was discontinued, and oral prednisolone (60 mg/day) was started. Subsequently, a tingling pain appeared on the right scalp. He was treated with valacyclovir (3 g/day for one week). Dysphagia and extremity weakness gradually improved after rehabilitation. On day 14, after admission, the patient was transferred to a university hospital for further investigation and advanced rehabilitation.

Discussion

This case showed the possibility of hypoglossal nerve palsy as a rare complication of COVID-19 vaccination, specific neurological complications following COVID-19 vaccination, and the rapid treatment of mononeuritis multiplex to prevent symptom progression.

The relationship between the COVID-19 vaccine and mononeuritis multiplex has been discussed in various studies. Several case reports have shown an increased risk of mononeuritis multiplex within a few days to months after COVID-19 vaccination [8,9]. A review of COVID-19 vaccination also showed that most symptoms related to mononeuritis multiplex were mild and disappeared naturally [10]. However, some cases show severe symptoms that affect the patient’s activities of daily life and require intensive treatment [7,11]. Our patient initially had mild symptoms and did not require treatment for his vital symptoms. However, within one week, the symptoms progressed drastically from the tongue to the extremities, causing difficulties in walking. The clinical course of mononeuritis multiplex varies, and some cases caused by vasculitis from autoimmune and infectious diseases may be progressive [5,12]. Precise follow-up and prompt treatment with intravenous immunoglobulins and steroids should be initiated to prevent disease progression.

Hypoglossal nerve palsy could be a rare symptom following COVID-19 vaccination and warrants further investigation in future studies. Among the complications of COVID-19 vaccination, various neurological complications were reported in 2020 [9,10]. Guillain-Barre syndrome is a well-known but rare complication of COVID-19 vaccination and appears a few weeks after vaccination [13]. Other cranial nerves may also be involved in the complications of COVID-19. Several case reports and reviews have reported facial palsy, the pain of the trigeminal and facial nerves, and diplopia of the oculomotor nerves [10,14]. However, hypoglossal nerve palsy is rare, and its pathophysiology remains unclear. In the present case, the initial finding was difficulty in tongue movement caused by palsy of the hypoglossal nerves, which led to systemic neurological symptoms. Clinicians should consider assessing single cranial symptoms following COVID-19 because of the possible spread of multiple nerve symptoms, causing a decreased quality of life.

The COVID-19 pandemic may persist in the future; therefore, preventable measures are vital. Vaccination is a critical measure for prevention. Although various complications have been reported, they are rare; therefore, vaccination should be promoted [15,16]. However, the possible symptoms following COVID-19 vaccination should be appropriately described, and help-seeking behaviors (HSB) to medical facilities should be facilitated, especially in rural contexts lacking healthcare resources [17-19]. The patient in the present case was younger, but the duration of his visit to the hospital was nearly two weeks. Early treatment could have prevented symptom progression [14]. When the same symptoms occur in older patients, HSB varies and is challenging, causing a greater delay in treatment. Citizens and healthcare professionals should be educated regarding responses to symptoms following vaccination, and information provision should be promoted [20].

Conclusions

Hypoglossal nerve palsy may be a symptom of COVID-19 vaccination. The symptoms vary and may progress without treatment. Physicians should consider the possibility of mononeuritis multiplex after COVID-19 vaccination and provide prompt treatment for acute symptom progression.


References

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  4. Tanemoto M, Hisahara S, Hirose B, et al.: Severe mononeuritis multiplex due to rheumatoid vasculitis in rheumatoid arthritis in sustained clinical remission for decades. Intern Med. 2020, 59:705-10. 10.2169/internalmedicine.3866-19
  5. Tokonami A, Ohta R, Katagiri N, Yoshioka N, Yamane F, Sano C: Autoimmune vasculitis causing acute bilateral lower limb paralysis. Cureus. 2022, 14:e27651. 10.7759/cureus.27651
  6. Enrique E-R, Javier B, Hernando R, Herney Andrés G: Mononeuritis multiplex associated with SARS-CoV2-COVID-19 infection: case report. Int J Neurol Neurother. 2020, 7:102. 10.23937/2378-3001/1410102
  7. Needham E, Newcombe V, Michell A, et al.: Mononeuritis multiplex: an unexpectedly frequent feature of severe COVID-19. J Neurol. 2021, 268:2685-9. 10.1007/s00415-020-10321-8
  8. Andalib S, Biller J, Di Napoli M, et al.: Peripheral nervous system manifestations associated with COVID-19. Curr Neurol Neurosci Rep. 2021, 21:9. 10.1007/s11910-021-01102-5
  9. Taga A, Lauria G: COVID-19 and the peripheral nervous system. A 2-year review from the pandemic to the vaccine era. J Peripher Nerv Syst. 2022, 27:4-30. 10.1111/jns.12482
  10. Finsterer J, Scorza FA, Scorza C, Fiorini A: COVID-19 associated cranial nerve neuropathy: A systematic review. Bosn J Basic Med Sci. 2022, 22:39-45. 10.17305/bjbms.2021.6341
  11. Oaklander AL, Mills AJ, Kelley M, Toran LS, Smith B, Dalakas MC, Nath A: Peripheral neuropathy evaluations of patients With prolonged long COVID. Neurol Neuroimmunol Neuroinflamm. 2022, 9:10.1212/NXI.0000000000001146
  12. Abdelhakim S, Klapholz JD, Roy B, Weiss SA, McGuone D, Corbin ZA: Mononeuritis multiplex as a rare and severe neurological complication of immune checkpoint inhibitors: a case report. J Med Case Rep. 2022, 16:81. 10.1186/s13256-022-03290-1
  13. Raahimi MM, Kane A, Moore CE, Alareed AW: Late onset of Guillain-Barré syndrome following SARS-CoV-2 infection: part of ‘long COVID-19 syndrome’?. BMJ Case Rep. 2021, 14:10.1136/bcr-2020-240178
  14. Hasan I, Saif-Ur-Rahman KM, Hayat S, et al.: Guillain-Barré syndrome associated with SARS-CoV-2 infection: A systematic review and individual participant data meta-analysis. J Peripher Nerv Syst. 2020, 25:335-43. 10.1111/jns.12419
  15. Machida M, Nakamura I, Kojima T, et al.: Acceptance of a COVID-19 vaccine in Japan during the COVID-19 pandemic. Vaccines (Basel). 2021, 9:10.3390/vaccines9030210
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  20. Ohta R, Ryu Y, Kitayuguchi J, Sano C, Könings KD: Educational intervention to improve citizen’s healthcare participation perception in rural Japanese communities: A pilot study. Int J Environ Res Public Health. 2021, 18:10.3390/ijerph18041782

Impact of Systemic Diseases on Olfactory Function in COVID-19 Infected Patients

Authors: Ayat A Awwad,1 Osama MM Abd Elhay,2 Moustafa M Rabie,3 Eman A Awad,4 Fatma M Kotb,4 Hend M Maghraby,4 Rmadan H Eldamarawy,4 Yahia MA Dawood,1 Mostafa IEI Balat,1 Ahmed IM Hasan,5 Ahmed H Elsheshiny,6 Said SMM El Sayed,2 Albayoumi AB Fouda,2 Ahmad MF Alkot2 DovPress November 7, 2022

1Otorhinolaryngology department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt; 2Medical Physiology Department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt; 3Public Health and Community Medicine Department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt; 4Internal medicine department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt; 5Pediatric Department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt; 6Neurology department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Correspondence: Ayat A Awwad, Otorhinolaryngology department, Faculty of Medicine, Al-Azhar University, Al Zhraa University Hhospital, Alabasia, Cairo, 11517, Egypt, Email ayatnasr7419@yahoo.com; dr.ayat@azhar.edu.eg Osama MM Abd Elhay, Medical Physiology Department, Faculty of Medicine, Al-Azhar University, Cairo, Egypt, Email osama.m.m.abdelhay@gmail.com; osamaabdelhay@domazhermedicine.edu.eg

Background: COVID-19 (SARS-CoV-2/2019-nCoV) is now a major public health threat to the world. Olfactory dysfunctions (ODs) are considered potential indicating symptoms and early case identification triaging for coronavirus disease 2019 (COVID-19). The most common reported comorbidities are diabetes mellitus, chronic lung disease, and cardiovascular disease. The objective of this study was to evaluate prevalence of different types of smell disorders in patients with laboratory-confirmed COVID-19 infection and impact of involved systemic diseases.
Methodology: A cross-sectional retrospective study has been done for patients with laboratory-confirmed COVID-19 infection (mild-to-moderate). The data collected from patient’s files and developed online electronic questionnaire (WhatsApp) based on the patients most common and recurrent reported data including: a) symptoms of olfactory dysfunction and associated covid19 symptoms fever and headache, cough, sore throat, pneumonia, nausea, vomiting and diarrhea, arthralgia and myalgia and taste dysfunction. b) Associated systemic diseases including: diabetes, hypertension, asthma, chronic renal disease, chorionic liver disease and hypothyroidism.
Results: Of 308 patients confirmed with Covid-19 infection, (72.4%) developed OD distributed as follows; complete anosmia (57.8%), troposmia (8.4%), hyposmia (2.9%), partial anosmia (2.6%) and euosmia (0.6%). Significantly increased prevalence of diabetes, hypertension asthma in the group with olfactory dysfunction (p < 0.001), chronic liver disease (p = 0.005), and hypothyroidism (p = 0.03).
Conclusion: The development of ODs after Covid-19 infection was associated with mild disease form and lower hospitalization. In addition, it showed significant relationship with preexisting systemic diseases. Anosmia is the common modality of ODs.

Keywords: COVID-19, anosmia, olfactory dysfunction

Introduction

World Health Organization (WHO) declared coronavirus disease 2019 (COVID-19) to be pandemic after it quickly spread all over the world.1 The involved cause is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).2 Human-to-human transmission is extremely rapid.3 Coronavirus is contagious with an incubation period ranging from 2 to 14 days. Through this period, patients can transmit infection even if asymptomatic.4

Asia reported that the most prevalent symptoms as: fever, myalgia, arthralgia cough, dyspnea, headache, diarrhea, rhinorrhea, and sore throat.5 Also, respiratory complications as pneumonia, lung fibrosis, and even death have been reported.6 Later, atypical presentation of the disease is widely observed including olfactory and gustatory malfunction but without rhinorrhea or nasal obstruction which are usually associated to other respiratory viral infections.7

WHO considers smell disorders as key symptoms of COVID-19.8 The American Academy of Otolaryngology–Head and Neck Surgery Foundation, 20209 together with Ear, Nose, and Throat Society of the United Kingdom (ENTUK) recommended self-isolation for patients presenting with these clinical features. Many countries reported the association smell disorder and taste with COVID-1910–12, but evidence remains controversial. In addition, none of them was concerned the incidence of different types of dysfunction.

COVID-19 virus appears to be more severe in severe older people and people with systemic conditions (such as diabetes, hypertension and asthma).13

The previous studies confirmed on olfactory dysfunction alone, neither its types nor impact of chronic diseases on OD so the aim of this study is to evaluate prevalence of different types of smell disorders in patients with laboratory-confirmed COVID-19 infection and impact of involved systemic diseases on ODs.

Methodology

The study was approved from Ethical Committee of the Faculty of medicine of Al-Azhar University (IRP) which complies with the Declaration of Helsinki. A cross-sectional retrospective study to patients with laboratory-confirmed COVID-19 infection (mild-to-moderate) who admitted in Al – Azhar University hospitals, fever hospitals, in addition to some of our patient’s clinics in Cairo, Egypt between the period from June 2020 to December 2020. The patients were divided into asymptomatic and symptomatic. The severity of the symptomatic diseases was classified into mild, moderate and severe.14

Informed consent was obtained from all patients (or a parent or legal guardian of patients under 18 years of age). The data collected from patient’s files and developed online electronic questionnaire (WhatsApp). Electronic questionnaire was designed by Professional otorhinolaryngologist, so that each participant could complete the survey. Questionnaire was based the patients most common and recurrent reported data including:

  • 4 items for assessment of ODs including: presence of smell dysfunction (yes or no), types of smell dysfunction (anosmia, hyposmia, partial anosmia, euosmia and troposmia).
  • 8 items for symptoms associated with covid-19 including: fever, headache, cough, sore throat, pneumonia, nausea, vomiting, diarrhea, arthralgia, myalgia and taste dysfunction (yes/no)
  • 6 items for associated systemic diseases including: diabetes, hypertension, asthma, chronic renal disease, chorionic liver disease and hypothyroidism (yes or no)

Inclusion criteria were: (> 12 years old of both genders); laboratory-confirmed COVID-19 infection (reverse transcription polymerase chain reaction, RT-PCR); native speaker patients, and patients clinically able to fulfill the questionnaire.

Patients with history of smell disorders, and not confirmed COVID-19, were unable to fulfill the questionnaire in addition to patients admitted to intensive care were also excluded from the study.

The data were collected, tabulated, and analyzed by Statistical Package for Social Sciences (version 21; SPSS Inc., Chicago, IL, USA). Two types of statistics were done:

  • Descriptive statistics [eg percentage (%), mean (x) and standard deviation (SD)],
  • Analytic statistics: which include the following:
    1. Chi-square test (χ2): was used to indicate presence or absence of a statistically significant difference between two qualitative variables.
    2. P-value of <0.05 was considered statistically significant.

Results

Demographic characteristics, comorbidities, and symptoms at the onset were reported in all patients confirmed with COVID-19 as shown in Table 1.

Table 1 Characteristics of Study Participants (N = 308)

The prevalence of ODs were 72% (223) with anosmia being the most common presented type (57.8%) while euosmia was the least presented type being only in (0.6%) as shown in Table 2 and Figure 1.

Table 2 Prevalence of Different Types of Olfactory Dysfunction Among COVID-19 Infected Patients (N = 308)

Figure 1 Prevalence of olfactory dysfunction types among cases who suffers from this dysfunction.

The frequency of ODs were significantly high with increasing in age (P value =0.000). But there was no significant difference between genders (P value =0.167) as reported in Table 3. Significant increases in different types of ODs with increasing in age (P value =0.000) while, there was no significant difference regarding gender (P value = 0.564) as shown in Table 4. Anosmia was the commonest presenting type of smell dysfunction in both genders (Figure 2).

Table 3 Frequency Distribution of Olfactory Dysfunction Occurrence According to Age and Sex

Table 4 Frequency Distribution of Olfactory Dysfunction Types in Relation to Age and Sex

Figure 2 Percent distribution of olfactory dysfunction types according to sex.

Regarding to other symptoms, the frequency of ODs were significantly associated to fever and headache, arthralgia, myalgia, taste dysfunction (P value =0.000), cough (P value =0.001), sore throat (P value =0.037), diarrhea, nausea and vomiting (P value =0.002). But it was not significantly associated with Pneumonia (P value =0.077) as shown in Table 5. ODs were the only presenting symptoms in 59.7% of patients Figure 3.

Table 5 Frequency Distribution of Olfactory Dysfunction Occurrence According to the Other Symptoms Experienced

Figure 3 Percent distribution of olfactory dysfunction as the only presenting symptom.

The frequency of ODs were significantly associated with diabetes, hypertension, asthma (P value=0.000), chronic liver disease, hypothyroidism (P value =0.003) and chronic renal disease (P value =0.005) as reported in Table 6. The different types of smell dysfunction showed significant association with asthma, chronic renal disease (P value =0.000), diabetes (P value =0.003), and hypertension (P value =0.002) while, there was no significant association with chronic liver disease and hypothyroidism (P value =0.158 and 0.524 respectively). Anosmia was the most common type of OD in association with diabetes, hypertension, asthma and chronic liver disease while, troposmia was the most common type of OD associated with chronic renal disease. The only case presented with euosmia was reported in chronic liver disease Table 7.

Table 6 Frequency Distribution of Olfactory Dysfunction Occurrence According to the Different Comorbidities

Table 7 Frequency Distribution of Olfactory Dysfunction Types in Relation to the Comorbidities

Discussion

The CDC (Center for Disease Control and Prevention) has highlighted the loss of smell as a significant symptom of COVID-19. In addition, recent research has indicated that OD may serve as an early clinical manifestation of this contagious.15–17

The current study was conducted to study the prevalence of different types of olfactory disorders in patients with laboratory-confirmed COVID-19 infection and its relationship with preexisting systemic comorbidities. Handling the effects of systemic comorbidities on olfactory manifestations in Covid-19 patients is poorly discussed in the literature. This poses a strong point in favor of our study.

We included a total of 308 patients confirmed with Covid-19 infection, 223 patients from them developed olfactory dysfunction (72.4%). When analyzing OD encountered in our research, it was distributed as follows; complete anosmia (57.8%), troposmia (8.4%), hyposmia (2.9%), partial anosmia (2.6%) and euosmia (0.6%). This is in line with multiple previous studies which reported that smell alternations are frequent manifestations of Covid-19 infection, with a prevalence ranging from 19.4% to 88%.3,12,13

This prevalence appears to be widely different between different studies. Mao et al reported lower prevalence (5%) in China18 and Marzano et al (18%) in Italy.19 Others reported much higher prevalence, reaching up to 98% in the study of Moein et al20 and 100% in the study of Heidari et al21 in Iran. This great heterogenicity could be explained by different sample sizes, patient characteristics, and methods of evaluating OD. In addition, Meng et al22 reported the difference of incidence in different countries as COVID-19 has three central variants A, B and C. Variants A and C which affect the nasal cavity causing OD were prevalent in Europe and America. Beside, human species affects significantly the susceptibility for infection.

Brann et al23 suggested that OD associated with Covid-19 infection is due to viral invasion of olfactory epithelial cells and vascular pericytes, which will negatively impact olfactory neuronal function. Additionally, nasal inflammation, congestion, and swelling may prevent olfactory molecules from reaching the olfactory cleft. Therefore, this conductive malfunction may play a role in developing OD.24

Lechien et al25 study handling the same perspective, the encountered OD was distributed as follows; anosmia (79.6%), while the remaining cases had hyposmia (20.4%). In another study, Vaira et al26 reported that among the Covid patients diagnosed with olfactory dysfunction, mild, moderate, and severe hyposmia was detected in 76, 59, and 45 patients, respectively. In addition, the remaining 61 cases had anosmia. It is expected to find some differences between different studies regarding the type of olfactory function diagnosed, according to the sample population included and criteria used to define each type.

In the current study, a significant difference was noted between patients with and without OD regarding patient age (p < 0.001), which tended to be significantly younger in the OD group. On the contrary a previous meta-analysis by Desiato et al17 has against this relationship. Several mechanisms could explain this association between advancing age and declining olfactory function including, nasal epithelial atrophy, olfactory bulb shrinkage, cribriform plate changes, in addition to age-associated cortical degeneration.27–29,30

However, another study by Mercante et al31 reported that the severity of OD was significantly increased in younger individuals, while older ones expressed mild or no symptoms. This confirms our findings.

Our findings showed no significant impact of gender on the development of this complication (p = 0.167). Thakur et al25 confirmed the previous findings regarding the insignificant association between gender and OD (p = 0.59). On the other hand, a recent meta-analysis by Saniasiaya et al32 had shown that the female gender is a risk factor for this manifestation, as it showed higher predominance compared to men. Researchers attributed that finding to the sex-related difference in the inflammatory process.33 Additionally, female patients were more sensitive than males to detect small alternations.32

Our findings showed a significant association between OD and fever, which is more prevalent in patients with this complication. In accordance with the previous results, Lechien et al25 reported a significant positive association between OD and fever (p < 0.001).

In the current study, the headache was significantly more prevalent in patients with OD (p < 0.001). This coincides with multiple previous studies which confirmed the association between headache and olfactory disturbances.34,35 This association was explained by either CNS involvement by the virus itself or hypoxic headache, which results from nasal congestion, which is associated with a decrease in olfactory function.36,37

In our study, taste dysfunction was significantly more encountered in patients with olfactory disturbances. This was confirmed before; as Lechien et al26 reported a significant positive association between both olfactory and gustatory functions (p < 0.001). Also Speth et al38 confirmed the previous findings.

In the current study, one could notice the significantly higher prevalence of other clinical findings (including sore throat, cough, diarrhea, nausea, vomiting, arthralgia, and myalgia) in association with OD.

Likewise, Talavera et al39 also reported the significant relationship between anosmia, myalgia, and cough in patients with Covid disease (p = 0.006). Nevertheless, other manifestations did not express a significant association with olfactory disturbances (p > 0.05).

Conversely, Yan et al12 reported that olfactory dysfunction was associated with a mild disease form. Moreover, another study Izquierdo-Domínguez et al40 reported that the same dysfunction was associated with lower C-reactive protein levels and a lower need for hospitalization.

Our findings showed significantly increased diabetes prevalence in the group with OD (p < 0.001). Although there is a paucity of studies handling the link between diabetes and OD in Covid-19 patients, the association between diabetes and the development of such dysfunction is well documented in a recent meta-analysis by Kim et al.41

Multiple mechanisms could induce this, including olfactory neurodegeneration and diabetes-associated microvascular disease.22,42,43 Of course, with the presence of these diabetes-associated factors, catching Covid-19 infection will increase the chance of having that dysfunction, especially in diabetic personnel. It was previously reported that the diabetic population is at high risk of having OD compared to healthy controls (OR = 1.58).41 In contrast to the previous findings, Talavera et al39 noted no significant impact of diabetes on the development of anosmia (p = 0.448). It was present in 17.1% and 20.5% of patients with and without anosmia, respectively.

Our findings showed that olfactory disturbances were significantly associated with hypertension (p < 0.001). Hypertension was present in 23.3% and 3.5% of patients with and without this dysfunction. We are the first researchers to report that finding in Covid-19 patients to the best of our knowledge. Our finding is supported by the accumulating evidence supporting the association between OD and cardiovascular disease.44,45 Several theories could explain this association; cardiovascular disease is common in the elderly, which is associated with degenerative neuronal changes, as discussed before. Also, the proinflammatory cytokines present with atherosclerosis could decrease olfactory function. Furthermore, some cardiovascular medications have a negative impact on hearing.46,47,48

In a recent study conducted in 2021, hypertensive patients expressed a lower prevalence of OD (p < 0.001), which was present in 74.9% and 88% of patients without and with hypertension, respectively.3 This is in contrast with our findings. In fact, the role of hypertension and the potential intake of angiotensin-converting enzyme inhibitors in the development of OD need to be well discussed in the upcoming studies.

In the current study, the prevalence of asthma showed a significant increase in patients with OD (p < 0.001). Asthma and olfactory impairment have never been linked, according to a recent report published in 2021 by Rhyou et al.48 However, the presence of allergic rhinitis or sinusitis in association with asthma surely decreases the olfactory sensation.29,49

Another study negated any significant difference between the anosmia and non-anosmia groups regarding the prevalence of respiratory diseases, which was present in 19.9% and 27% of patients in the same groups, respectively (p = 0.109).39

Our findings showed a higher prevalence of chronic liver disease in association with anosmia (p = 0.003). Previously, Heiser et al50 reported that olfactory deficits are frequently encountered in patients with cirrhosis. This functional decline is the result of calorie, protein, and micronutrient deficiency in such patients.51 This evidence was supported by the improvement of this function after liver transplantation, as reported by Bloomfield et al.52

In the current study, the prevalence of chronic kidney disease was significantly higher in association with OD (p = 0.005). In fact, patients with such comorbidities often complain of olfactory impairment, which could be the consequence of malnutrition and decreased fluid intake.53,54 Uremia itself could induce neuropathy and decreased smell sensation.54

Our findings showed that hypothyroidism was significantly more common in the OD group (p = 0.03). In line with the previous findings, Tsivgoulis et al55 have reported that hypothyroidism is associated with more prolonged Covid-19 induced anosmia. Sorrily, there is no clear data about whether hypothyroidism can induce OD in adult humans.56

Our study has some limitations; we should have evaluated the impact of OD on patient outcome and long-term nasal function. In addition to this retrospective study may together have some bias to mention. This study did not perform an objective olfactory test on the patients but was based on an electronic questionnaire, which may affect the accuracy of the survey.

All in all, based on our findings, complete anosmia was the most presented modality of OD. Fever, headache, taste dysfunction, sore throat, cough, diarrhea, nausea, vomiting, arthralgia, and myalgia were common symptoms associated with OD. Mild disease form, low C-reactive protein and lower need for hospitalization were common association with OD. Significant increases in incidence of OD in diabetes mellitus, hypertension, bronchial asthma, chronic liver disease, chronic kidney disease and hypothyroidism. Lower incidence of respiratory symptoms in anosmia compared to non-anosmia group.

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32. Saniasiaya J, Islam MA, Abdullah B. Prevalence of olfactory dysfunction in coronavirus disease 2019 (COVID-19): a meta-analysis of 27,492 patients. Laryngoscope. 2021;131(4):865–878. doi:10.1002/lary.29286

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36. Hatton CF, Duncan CJA. Microglia are essential to protective antiviral immunity: lessons from mouse models of viral encephalitis. Front Immunol. 2019;10:2656. doi:10.3389/fimmu.2019.02656

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38. Speth MM, Singer-Cornelius T, Oberle M, Gengler I, Brockmeier SJ, Sedaghat AR. Olfactory dysfunction and sinonasal symptomatology in COVID-19: prevalence, severity, timing, and associated characteristics. Otolaryngol Head Neck Surg. 2020;163(1):114–120. doi:10.1177/0194599820929185

39. Talavera B, García-Azorín D, Martínez-Pías E, et al. Anosmia is associated with lower in-hospital mortality in COVID-19. J Neurol Sci. 2020;419:117163. doi:10.1016/j.jns.2020.117163

40. Izquierdo-Domínguez A, Rojas-Lechuga MJ, Chiesa-Estomba C, et al. Smell and taste dysfunction in COVID-19 is associated with younger age in ambulatory settings: a multicenter cross-sectional study. J Investig Allergol Clin Immunol. 2020;30(5):346–357. doi:10.18176/jiaci.0595

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What Is COVID Tongue, and What Does It Mean?

Authors: Medically reviewed by Elizabeth Thottacherry, MD — By S. Behring — Updated on January 20, 2022 HealthLine

In March 2020, the World Health Organization (WHO) declared a pandemic in response to the spread of the COVID-19 infection.

Since then, more than 50 million casesTrusted Source occurred in the United States alone. Medical professionals gathered data to determine the symptoms of COVID-19. The early symptoms observed included fatigue, shortness of breath, and fever.

But as COVID-19 cases continue, new symptoms are documented, including a rare symptom known as COVID tongue. People with COVID tongue have swollen tongues that might develop bumps, ulcers, and white patches. Read on to learn more about this unusual COVID-19 symptom.

What is COVID tongue?

Along with the more well-known symptoms of COVID-19, some people experience bumps, ulcers, swelling, and inflammation of the tongue. This is known as “COVID tongue.”

People with COVID tongue might notice that the top of their tongue looks white and patchy, or that their tongue looks red and feels swollen. They sometimes find bumps or open areas called ulcers on their tongue. Additionally, many people with COVID tongue report experiencing a loss of taste and a burning sensation in their mouth.

2021 study documented COVID tongue as a possible COVID-19 symptom. But just like many things about COVID-19, there’s a lot we don’t know right now about COVID tongue.

What’s happening inside your body to cause COVID tongue?

Another reason there are many questions about COVID tongue is that there are several possible causes. It’s common for illnesses and infections to cause changes to your tongue.

What looks like COVID tongue could easily be a symptom of a different viral or bacterial infection. Even when the bumps and swelling are clearly connected to COVID, there are many possible reasons. COVID tongue might be caused by:

  • A high number of ACE receptors in your tongue. ACE receptors are proteins found on cells in your body. When the virus that causes COVID-19, SARS-CoV-2, attaches to ACE receptors, it can get into your cells. You have many ACE receptors in your tongue, which could lead to swellingTrusted Source when you have a COVID-19 infection.
  • Your immune system fighting COVID-19. When your immune system is fighting a bacterial or viral infection, it can cause swelling throughout your body. This could include the tongue swelling associated with COVID tongue.
  • COVID-causing oral thrush. Oral thrush is a fungus in your mouth that can be caused by a number of infections. This might include COVID-19. Plus, oral thrush is a side effect of some medications used to treat COVID-19.
  • Changes to the surface of your tongue. Infections sometimes lead to changes on the surface of your tongue, such as mouth ulcers and other symptoms. It’s possible COVID-19 can lead to this sort of change as well.
  • Dry mouth. COVID-19 can affect your salivary glands and cause them to secrete less saliva. This could lead to dry mouth. Research shows that dry mouth can lead to multiple other oral health concerns.
  • COVID-activating oral herpes. The inflammation caused by COVID-19 can activate other viruses in your body. This might include the herpes simplex virus, which lays dormant in your body even when you don’t have symptoms. COVID-19 could causeTrusted Source the herpes virus to activate and cause mouth ulcers.

COVID tongue could be caused by any one of these factors or by a combination of them. There’s also a chance that COVID tongue is sometimes caused by breathing tubes and other COVID treatments that could irritate your mouth and lead to a swollen tongue.

Until we know more about COVID-19, we won’t know the exact cause of COVID tongue.

How many people get COVID tongue?

Currently, scientists don’t know how rare COVID tongue is. In one small study, up to 11 percent of people hospitalized with COVID-19 had COVID tongue, but such studies are too small to make a conclusion.

As more data from hospitals around the world come in, we might get a better idea of how common COVID tongue is.

Many people with COVID-19 have mild or moderate symptoms and can recover at home. But right now, even less is known about how many people in this group develop COVID tongue. Often they recover without contacting a doctor at all, so their symptoms are never recorded.

Even when people with mild or moderate COVID-19 do seek treatment, they often wear masks or use telehealth for a video appointment. That makes it difficult for medical professionals to see their tongues and document any abnormalities.

What is the treatment for COVID tongue?

There is currently no single set treatment for COVID tongue. You might not need treatment targeted to COVID tongue. In some cases, the treatments you already receive for COVID will be enough to resolve COVID tongue.

When COVID tongue is more severe and doesn’t respond to overall treatment, you might receive specialized treatment. This could include:

  • corticosteroids or other anti-inflammatory medications to bring down tongue swelling
  • antibacterial, antiviral, or antifungal mouth rinses to treat bumps, patches, and ulcers
  • artificial saliva mouth rinses to help combat dry mouth and promote overall tongue healing
  • low level laser therapy to treat ulcers

Treatment for swollen tongue

COVID-19 may cause the tongue to swell. Tongue swelling can quickly become a medical emergency if your airway becomes blocked. If you think your tongue is swelling, seek medical attention immediately.

The treatment for a swollen tongue is designed to reduce the swelling and relieve pain and discomfort.

Treatment options for swollen tongue include:

  • over-the-counter medications such as ibuprofen (Advil)
  • prescription anti-inflammatory medications
  • medications to treat the underlying condition causing your tongue to swell

What to do if your tongue swells

Call 911 if your tongue swells and you feel like it’s harder to breathe. Do not drive yourself to the ER because your condition could worsen on the way. For many people, calling 911 means help will reach you faster than going to an ER.

  • Have someone stay with you until help arrives.
  • Contact your healthcare professional immediately if you notice that your tongue swells.
  • If you have mild tongue swelling that gets worse, contact your doctor or healthcare professional immediately for an examination.

What’s the outlook for people with COVID tongue?

It’s currently unclear whether COVID tongue is an early symptom of COVID-19, or a symptom that develops as the condition progresses.

No matter when it develops, you might also have other, more-common COVID-19 symptoms:

  • fever
  • cough
  • shortness of breath
  • fatigue
  • nausea
  • pain

Studies are being done to see if COVID tongue is an early or warning symptom.

Mild to moderate COVID-19

People with mild and moderate cases of COVID-19 usually recover at home without medical intervention. Rates of recovery are also improving for people hospitalized with COVID-19 as doctors learn how to best treat the infection.

But since COVID-19 is still a relatively new illness, we don’t know for sure right now what the long-term effects for people will be. Some symptoms of COVID-19 might linger for weeks or even months.

Geographic tongue

While research on COVID tongue is limited now, we do know that viral infections can sometimes lead to a condition called geographic tongue.

This condition causes smooth red patches with white borders to appear on your tongue and can last for months — or even years. Geographic tongue doesn’t generally cause pain or other health concerns, but flare-ups can make it difficult to eat spicy foods.

It’s currently unclear whether COVID tongue is related to geographic tongue, or whether COVID-19 can lead to geographic tongue. As more people recover from COVID-19 and more data become available, doctors will have a better understanding of COVID tongue and any possible long-term effects.

If you have COVID-19 and are experiencing any mouth or tongue health concerns, talk with your doctor.

The bottom line

Some people with COVID-19 develop bumps, white patches, and swelling on their tongues. This is known as COVID tongue and it’s still being studied.

Right now, there are a lot of unanswered questions about COVID tongue. We currently don’t know how many people get COVID tongue or what causes it. More information about COVID tongue will be available as doctors learn more about COVID tongue and more research occurs.

How COVID-19 causes neurological damage found

Particularly in the group with the most serious neurological symptoms, the researchers identified a link with an excessive immune response.

Authors: PTI 15th November 2022 The Indian Express

COVID-19 may cause damage to the nervous system, even though it does not affect nerve cells, according to a small study.

While it was not uncommon for some people to lose their sense of taste and smell due to a Covid-19 infection, in others, the disease had had an even stronger impact on the nervous system, with effects ranging from lasting concentration problems to strokes, the study said.

Researchers, from the University of Basel and University Hospital Basel, Switzerland, have studied the mechanisms responsible for and reported new insights into the development of “neuro-Covid”, including identifying starting points for its prevention, the study said.

The team investigated how different severities of neuro-COVID can be detected and predicted by analyzing the cerebrospinal fluid and blood plasma of affected individuals.

Their findings, published in the journal Nature Communications, also indicate how to prevent neurological damage due to Covid-19.

The study included 40 Covid-19 patients with differing degrees of neurological symptoms.

n order to identify typical changes associated with neuro-Covid, the team of researchers compared cerebrospinal fluid and blood plasma of these individuals with samples from a control group.

They also measured the brain structures of test subjects and surveyed participants 13 months after their illness in order to identify any lasting symptoms.

Particularly in the group with the most serious neurological symptoms, the researchers identified a link with an excessive immune response.

On the one hand, the study said, affected individuals showed indications of impairment of the blood-brain barrier, which the study’s authors speculate was probably triggered by a “cytokine storm” — a massive release of pro-inflammatory factors in response to the virus.

On the other hand, the researchers also found antibodies that targeted parts of the body’s own cells — in other words, signs of an autoimmune reaction — as a result of the excessive immune response, the study said.

ALSO READ | Study: Blood tests might help to detect long covid in patients

“We suspect that these antibodies cross the porous blood-brain barrier into the brain, where they cause damage,” explained lead researcher Gregor Hutter.

Researchers also identified excessive activation of the immune cells specifically responsible for the brain — the microglia.

In a further step, Hutter and his team investigated whether the severity of neurological symptoms is also perceptible in brain structures.

Indeed, they found that people with serious neuro-Covid symptoms had a lower brain volume than healthy participants at specific locations in the brain and particularly at the olfactory cortex — that is, the area of the brain responsible for smell.

“We were able to link the signature of certain molecules in the blood and cerebrospinal fluid to an overwhelming immune response in the brain and reduced brain volume in certain areas, as well as neurological symptoms,” says Hutter, adding that it is now important to examine these biomarkers in a greater number of participants.

ALSO READ | Covid virus ‘more likely than not, result of a research-related incident’: US report

The aim, the study said, would be to develop a blood test that can already predict serious cases, including neuro-Covid and long Covid, at the start of an infection.

These same biomarkers point to potential targets for drugs aimed at preventing consequential damage due to a Covid-19 infection.

One of the biomarkers identified in blood, the factor MCP-3, plays a key role in the excessive immune response, and Hutter believes there is the potential to inhibit this factor medicinally, the study said.

“In our study, we show how coronavirus can affect the brain,” he says.

“The virus triggers such a strong inflammatory response in the body that it spills over to the central nervous system. This can disrupt the cellular integrity of the brain.”

Accordingly, Hutter said that the primary objective must be to identify and halt the excessive immune response at an early stage, the study said.ors

COVID-19 gave new urgency to the science of restoring smell

The sense may often be an afterthought, but its loss affects people deeply

Authors:  Laura Sanders Science News

It was the juice that tipped him off. At lunch, Ícaro de A.T. Pires found the flavor of his grape juice muted, flattened into just water with sugar. There was no grape goodness. “I stopped eating lunch and went to the bathroom to try to smell the toothpaste and shampoo,” says Pires, an ear, nose and throat specialist at Hospital IPO in Curitiba, Brazil. “I realized then that I couldn’t smell anything.”

Pires was about three days into COVID-19 symptoms when his sense of smell vanished, an absence that left a mark on his days. On a trip to the beach two months later, he couldn’t smell the sea. “This was always a smell that brought me good memories and sensations,” Pires says. “The fact that I didn’t feel it made me realize how many things in my day weren’t as fun as before. Smell can connect to our emotions like no other sense can.”

As SARS-CoV-2, the virus responsible for COVID-19, ripped across the globe, it stole the sense of smell away from millions of people, leaving them with a condition called anosmia. Early in the pandemic, when Pires’ juice turned to water, that olfactory theft became one of the quickest ways to signal a COVID-19 infection. With time, most people who lost smell recover the sense. Pires, for one, has slowly regained a large part of his sense of smell. But that’s not the case for everyone.

About 5.6 percent of people with post–COVID-19 smell loss (or the closely related taste loss) are still not able to smell or taste normally six months later, a recent analysis of 18 studies suggests. The number, reported in the July 30 British Medical Journal, seems small. But when considering the estimated 550 million cases and counting of COVID-19 around the world, it adds up.

Scientists are searching for ways to hasten olfactory healing. Three years into the COVID-19 pandemic, researchers have a better idea of how many people are affected and how long it seems to last. Yet when it comes to ways to rewire the sense of smell, the state of the science isn’t coming up roses.

A method called olfactory training, or smell training, has shown promise, but big questions remain about how it works and for whom. The technique has been around for a while; the coronavirus isn’t the first ailment to snatch away smell. But with newfound pressure from people affected by COVID-19, olfactory training and a host of other newer treatments are now getting a lot more attention.

The pandemic has brought increased attention to smell loss. “If we have to provide a silver lining, COVID is pushing the science at a speed that’s never happened before,” says Valentina Parma, an olfactory researcher and assistant director of the Monell Chemical Senses Center in Philadelphia. “But,” she cautions, “we are really far from a solution.”

Nasal attack

Compared with sight or hearing, the sense of smell can seem like an afterthought. But losing it can affect people deeply. “Your world really changes if you lose the sense of smell, in ways that are usually worse,” Parma says. The smell of a baby’s head, a buttery curry or the sharp salty sea can all add emotional meaning to experiences. Smells can also warn of danger, such as the rotten egg stench that signals a natural gas leak.

As an ear, nose and throat doctor, Pires recalls a deaf patient who lost her sense of smell after COVID-19 and enrolled in a clinical trial that he and colleagues conducted on smell training. She worked in a perfumery company — her sense of smell was crucial to her job and her life. “At the first appointment, she said, with tears in her eyes, that it felt like she wasn’t living,” Pires recalls.

Unlike the cells that detect color or sound, the cells that sense smell can replenish themselves. Stem cells in the nose are constantly pumping out new smell-sensing cells. Called olfactory sensory neurons, these cells are dotted with molecular nets that snag specific odor molecules that waft into the nose. Once activated, these cells send messages through the skull and into the brain.

Because of their nasal neighborhood, olfactory sensory neurons are exposed to the hazards of the environment. “They may be covered with a little layer of mucus, but they’re sitting out there being constantly bombarded with bacteria and viruses and pollutants and who knows what else,” says Steven Munger, a chemosensory neuroscientist at the University of Florida College of Medicine in Gainesville.

Exactly how SARS-CoV-2 damages the smell system isn’t clear. But recent studies suggest the virus’s assault is indirect. The virus can infect and kill nose support cells called sustentacular cells, which are thought to help keep olfactory neurons happy and fed by delivering glucose and maintaining the right salt balance. That attack can inflame the olfactory epithelium, the layers of cells that line parts of the nasal cavity.

Once this tissue is riled up, the olfactory sensory neurons get wonky, even though the cells themselves haven’t been attacked. After an infection and ensuing inflammation, these neurons slow down the production of their odor-catching nets, a decrease that could blind themselves to odor molecules, scientists reported in the March 17 Cell.

With time, the inflammation settles down, and the olfactory sensory neurons can get back to their usual jobs, researchers suspect. “We do think that for post-viral smell disorders, the most common way to recover function is going to be spontaneous recovery,” Munger says. But in some people, this process doesn’t happen quickly, if ever.

That’s where smell training comes in.

A nose workout

One of the only therapies that exists, smell training is quite simple — a good old-fashioned nose workout. It involves deeply smelling four scents (usually rose, eucalyptus, lemon and cloves) for 30 seconds apiece, twice a day for months. 

In one study, 40 people who had smell disorders came away from the training with improved smelling abilities, on average, compared with 16 people who didn’t do the training, olfactory researcher Thomas Hummel and his colleagues reported in the March 2009 Laryngoscope.

Since then, the bulk of studies has shown that the method helps between 30 and 60 percent of the people who try it, says Hummel, of Technische Universität Dresden in Germany. His view is that the method can help some people, “but it does not work in everybody.”

One of the nice things is that there are no harmful side effects, Hummel says. That’s “the charming side of it.” But to do the training correctly takes discipline and stamina. “If you don’t do it regularly, and you give up after 14 days, this is futile,” he says.

Pires in his recent trial had hoped to speed up the process, which usually takes three months, by adding four more odors to the regimen. For four weeks, 80 participants received either four or eight smells. Both groups improved, but there was no difference between the two groups, the researchers reported July 21 in the American Journal of Rhinology & Allergy.

It’s not known how the technique works in the people it seems to help. It could be that it focuses people’s attention on faint smells; it could be stimulating the growth of replacement cells; it could be strengthening some pathways in the brain. Data from other animals suggest that such training can increase the number of olfactory sensory neurons, Hummel says.

Overall, this nose boot camp may be a possible approach for people to try, but big questions remain about how it works and for whom, Munger says. “In my view, it’s very important to be up front with patients about the very real possibility this therapy may not lead to a restoration of smell, even if they and their doctor feel it is worth trying,” he says. “I am not trying to discourage people here, but I also think we need to be very careful not to give unwarranted promises.” 

Smell training doesn’t come with harmful biological side effects, but it can induce frustration if it doesn’t work, Parma says. In her practice, “I have been talking to a lot of people who say, ‘I did it every day for six months, twice a day for 10 minutes. I met in groups with other people, so we kept each other accountable, and I did that for six months. And it didn’t work for me.’” She adds, “I would want to address the frustration that this induces in patients.”

Beyond training

Other potential treatments are coming under scrutiny, such as steroids, omega-3 supplements, growth factors and vitamins A and E, all of which might encourage the recovery of the nasal epithelium.

More futuristic remedies are also in early stages of research. These include epithelial transplants designed to boost olfactory stem cells, treatments with platelet-rich plasma to curb inflammation and promote healing, and even an “electronic nose” that would detect odor molecules and stimulate the brain directly. This cyborg-smelling system takes inspiration from cochlear implants for hearing and retinal implants for vision. 

Selling smell short

People routinely undervalue the sense of smell. Some people rated the ability to smell as less important than various creature comforts, hair and even the little left toe, a recent survey found.

How many people would rather give up smell than these things:
bar chart of different commodities vs. percentage of people willing to give up smell instead
C. CHANG, ADAPTED FROM R.S. HERZ AND M.R. BAJEC/BRAIN SCIENCES 2022

For many people, the sense of smell is appreciated only after it’s gone, Parma says, an apathy that’s illustrated in stark terms by a recent study of about 400 people. The vast majority of respondents — nearly 85 percent — would rather give up their sense of smell than sight or hearing. About 19 percent of respondents said they would prefer to give up their sense of smell than their cell phone. The survey results “dramatically illustrate the negligible value people place on their sense of smell,” researchers wrote in the March Brain Sciences.

Even as a doctor who treats people with smell loss, Pires has a newfound fondness for a good whiff. “Having lost it for a while made me appreciate it even more.”    

CITATIONS

B.K.J. Tan et alPrognosis and persistence of smell and taste dysfunction in patients with COVID-19: meta-analysis with parametric cure modelling of recovery curvesThe British Medical Journal. Vol. 378, July 30, 2022. doi:10.1136/bmj-2021-069503.

M. Zazhytska et alNon–cell-autonomous disruption of nuclear architecture as a potential cause of COVID-19–induced anosmiaCell. Vol. 185, March 17, 2022, p. 1052. doi: 10.1016/j.cell.2022.01.024.

T. Hummel et alEffects of olfactory training in patients with olfactory lossLaryngoscope. Vol. 119, March 2009, p. 496. doi: 10.1002/lary.20101.

Í. de A.T. Pires et alIntensive olfactory training in post–COVID-19 patients: a multicenter randomized clinical trialAmerican Journal of Rhinology & Allergy. Published online July 21, 2022. doi: 10.1177/19458924221113124.

R.S. Herz and M.R. Bajec. Your money or your sense of smell? A comparative analysis of the sensory and psychological value of olfactionBrain Sciences. Vol. 12, March 2022, p. 299. doi: 10.3390/brainsci12030299.

What, Exactly, Is ‘Paxlovid Mouth’ and How Do You Get Rid of It?

The Covid-19 antiviral drug can leave a foul taste. The afflicted are scouring for remedies online.

Authors: Alex Janin Aug. 16, 2022 Wall Street Journal

Jeanette Witten recently rummaged through her pantry for Red Hots, the cinnamon-flavored candy.

The 56-year-old in Montclair, N.J., was looking for a reprieve from a persistent residual taste—“like your mouth is just clenched around a grapefruit rind”—that came after she took Paxlovid, Pfizer’s antiviral drug to treat Covid-19. 

Ms. Witten is one of many people who have scouted remedies for what is informally known as Paxlovid mouth, a taste that can linger for as long as you take the drug. Patients who have taken Paxlovid have described it as sun-baked trash-bag liquid, a mouthful of dirty pennies and rotten soymilk. They have tried to erase the taste with salves from cinnamon to milk to pineapple. They are also trading strategies online. 

Pfizer spokesperson acknowledged the side effect, called dysgeusia, and pointed to a study that found the symptom occurred 5.6% of the time people took the drug. The study was funded by Pfizer and published in the New England Journal of Medicine. The company said most patients’ dysgeusia symptoms were mild.

A weekly look at our most colorful, thought-provoking and original feature stories on the business of life.

The culprit is likely ritonavir, a part of the drug that is used to boost levels of antiviral medicines, doctors say. Ritonavir has a known association with dysgeusia. It is a small price to pay given the nearly 90% reduction in hospitalization and death among those at risk for severe disease from Covid-19, say doctors and people who have taken the medication. 

But it’s still hard for many patients to stomach.

Potential pharmacologic treatments for COVID-19 smell and taste loss: A comprehensive review

Authors: Elnaz Khani,aSajad Khiali,aSamineh Beheshtirouy,a and Taher Entezari-Malekia,b,∗

Eur J Pharmacol. 2021 Dec 5; 912: 174582.Published online 2021 Oct 19. doi:  10.1016/ j.ejphar.2021.174582 PMCID: PMC8524700PMID: 34678243

Abstract

The acute loss of taste and smell following COVID-19 are hallmark symptoms that affect 20–85% of patients. However, the pathophysiology and potential treatments of COVID-19 smell and taste loss are not fully understood. We searched the literature to review the potential pathologic pathways and treatment options for COVID-19 smell and taste loss. The interaction of novel coronavirus with ACE-2 receptors expressed on sustentacular cells and taste buds results in direct damage to the olfactory and gustatory systems. Also, the invasion of the virus to the olfactory neurons and consequent local inflammation are other proposed mechanisms. Therefore, COVID-19 patients with smell or taste loss may benefit from neuroprotective, anti-inflammatory, or depolarizing agents. Based on the current evidence, phosphodiesterase inhibitors, insulin, and corticosteroids can be promising for the management of COVID-19 smell and taste loss. This review provided crucial information for treating COVID-19-related smell and/or taste loss, urging to perform large clinical trials to find optimum treatment options.Keywords: Ageusia, Anosmia, COVID-19, Therapeutics.

1. Introduction

Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 210 million cases and 4 million deaths have been reported worldwide. Despite the considerable progress in treatment tools of the disease, effective therapies for managing the long-lasting complications of the novel coronavirus disease (COVID-19) are still lacking. It is now clear that COVID-19 is not just a respiratory disease and affects other parts of the body. The common manifestations of COVID-19 are fever, cough, and fatigue, which are nonspecific and make the diagnosis challenging (Huang et al., 2020). The acute loss of taste and smell are key diagnostic criteria supposed to be used as screening tools based on the National Institute on Deafness and Other Communication Disorders (NIDCD), and the Global Consortium for Chemosensory Research (GCCR) reports (Gerkin et al., 2021Lovato et al., 2020National Institute on Deafness and Other Communication Disorders, 2021Parma et al., 2020).

Anosmia and ageusia are categorized as neurological complications of the SARS-CoV-2 infection. Previous studies revealed that approximately 20–85% of COVID-19 patients experienced olfactory and gustatory dysfunctions (Bilinska and Butowt, 2020Mao et al., 2020). Although the clear causes of these complications are not fully understood, angiotensin-converting enzyme 2 (ACE2) expression and local inflammation have been considered key mechanisms (Giacomelli et al., 2020Lechien et al., 2020Spinato et al., 2020). Other suggested mechanisms were infecting olfactory non-neuronal cells and sensory neurons (Brann et al., 2020de Melo et al., 2021).

Given to paramount findings of COVID-19 smell and taste loss and lack of effective treatments, we aimed to review the potential treatments of COVID-19 smell and taste loss based on clinical pharmacology principles.

2. Pathophysiology of anosmia

Numerous probable mechanisms have been suggested for the COVID-19-related anosmia, such as nasal obstruction and rhinorrhea, olfactory cleft syndrome, local cytokine storm, damage to the olfactory centers in the brain, direct damage of olfactory receptor neurons (ORNs), also called olfactory sensory neurons (OSNs), or sustentacular cells (SUSs). However, most of them have been ruled out subsequently.

2.1. Damages to SUS and ORNs

In the normal olfactory system, odorant particles bind to the olfactory receptors; the ORN sends the smell sensation signal through the cribriform plate (bone) to the olfactory bulb, where they synapse to the dendrites of mitral and tufted cells. The normal function of ORNs depends on sustentacular cells (SUSs) of the olfactory epithelium (OE). In this regard, SUSs protect the ORNs through metabolizing volatile chemicals via expressing the cytochrome P450 family enzymes. Besides, SUSs could endocytose the complexes of odorant-binding proteins−odorant after initiation of signal transduction at the neurons’ cilia to let the next series of odorants bind to the receptors. Lastly, SUSs supply ORNs cilia with additional glucose, where olfactory receptors are found (Heydel et al., 2013Villar et al., 2017).

It is well-known that SARS-CoV-2 infectivity depends on the binding of spike (S) proteins to the host cells receptors of ACE2 and transmembrane protease serine 2 (TMPRSS2). After interaction with host cells receptors, the S proteins of the SARS-CoV-2 undergo conformational changes that lead to viral cell entry.

It has been shown that SUSs express ACE2 and TMPRSS2 that could result in the SARS-CoV-2 entry and consequential damages to the SUSs. Whereas ORNs do not express the entry proteins for the virus. Therefore, the direct damage to the SUSs could result in olfactory dysfunction without transfer to ORNs due to the functional and anatomical link between SUSs and ORNs. Moreover, Brann et al. showed that SARS-CoV-2 infection of non-neuronal cell types leads to olfactory dysfunction in COVID-19 patients (Brann et al., 2020Fodoulian et al., 2020).

Recently, in a study by de Melo et al., olfactory mucosa sampling revealed that SARS-CoV-2 invades both ORNs and SUSs in human and Syrian hamster models with COVID-19-related anosmia and ageusia. By investigating cell death in the olfactory neuroepithelium, this study considered the apoptosis of mature ORNs as the most relevant cause of anosmia in COVID-19 patients. Notably, they found that SARS-CoV-2 presents in the ORNs of COVID-19 patients with long-lasting anosmia even after six months from diagnosis. Although this study supported the ORNs damage and possible neuroinvasion as anosmia causes, further studies should precisely determine the olfactory bulb dysfunction using larger sample sizes and control groups (de Melo et al., 2021).

Bryche et al. have evaluated the effects of SARS-CoV-2 infection on the olfactory system in golden Syrian hamsters’ model. They observed considerable damage to the OE and loss of smell after two days of nasal instillation of the virus. However, they showed that, unlike the SUSs, the virus did not affect olfactory neurons and olfactory bulbs. They suggested that infiltrated immune cells in the OE may lead the OE to be desquamated and damaged. The restoration of the OE was achieved within 14 days after infection. Thus, this in-vivo study supported that sudden anosmia results from infected SUSs, leading to extended and quick damage to the OE and lamina propria due to immune cells (Bryche et al., 2020).

Meinhardt et al. investigated the brain samples of 32 patients who died of COVID-19. This study suggested that the virus affects the ORNs. However, by single immunocytochemical imaging, especially in old samples that were taken lately after death, the differentiation between neuronal and non-neuronal cells cannot be performed obviously. Moreover, the ribonucleic acid (RNA) of the virus was detected in only 3 of the olfactory bulb samples that did not strongly support the viral diffusion to the brain by the olfactory nerve. Also, lacking data about which patients experienced anosmia limits the interpretation of the results (Meinhardt et al., 2021).

2.2. Inflammation

Along with the damage to the SUSs, a rapid immune response in microvillar cells (MVCs) and a subset of ORNs leads to activation and infiltration of macrophages and lymphocytes into the OE, the release of pro-inflammatory cytokines, and occurrence of cytokine storm, which all may explain the sudden anosmia in patients with COVID-19. Notably, it seems that progenitor/stem cell infection is responsible for COVID-19 induced long-term dysosmia. It has been shown that a local excessive immune response and cytokine storm could lead to olfactory dysfunction even in patients with a milder form of the disease. Of note, to date, no adequate data support the rapid harm to the olfactory cortical areas in the brain; therefore, it is unlikely that excessive systemic immune response and inflammation in the brain have an essential role in the anosmia development (Baxter et al., 2021). In a study by Torabi et al., the direct role of inflammatory cytokines in acute olfactory dysfunction has been highlighted. In this study, the levels of tumor necrosis factor-alpha (TNF-α) in the OE were significantly higher in COVID-19 patients compared to the control group, whereas interleukin-1-beta (IL-1β) levels were similar between groups.

Furthermore, in other studies, SARS-CoV-2-induced infiltration of immune cells, including macrophages and granulocytes, into the OE has been reported (Bryche et al., 2020Meinhardt et al., 2021Torabi et al., 2020). Also, de Melo et al. considered local inflammation a key factor in COVID-19 patients with long-lasting olfactory dysfunction. They showed a high IL-6 expression and myeloid cells in the olfactory mucosa of these patients (de Melo et al., 2021).

2.3. Other probable mechanisms

Nasal obstruction and rhinorrhea, which could block nasal air-flow, are suggested to be much less common and have been ruled out as a cause of SARS-CoV-2 induced anosmia (Salmon Ceron et al., 2020). The interaction of SARS-CoV-2 with sialic acid receptors expressed in nasal mucosa can be another entry pathway other than ACE2 receptors, which might have a role in the complications of the virus, such as anosmia (Kuchipudi et al., 2021Milanetti et al., 2020).

The virus infiltration to the brain is another suggested mechanism in which the OSN is considered a direct route to the brain through anterograde axonal transport (Fenrich et al., 2020). Also, the reports of meningitis and encephalitis in some COVID-19 patients could support the idea that SARS-CoV-2 might invade the central nervous system (CNS). Magnetic resonance imaging could provide information about the olfactory bulb and possible CNS invasion of the virus. The olfactory bulb volume was normal in the first report of olfactory bulb magnetic resonance imaging in a patient with COVID-19-related anosmia (Galougahi et al., 2020). However, further studies showed changes in the volume and shape of the olfactory bulb in COVID-19 patients with anosmia (Altundag et al., 2020Kandemirli et al., 2021Politi et al., 2020).

3. Ageusia pathophysiology

Due to the close connection between olfactory and gustatory functions, it might be possible that the concomitant presence of olfactory dysfunction adversely influences the ability of taste perception in COVID-19 patients. However, different pathways have also been suggested, including direct damage to taste buds and salivary glands, binding to sialic acid receptors, and inflammation.

It has been shown that the taste buds and salivary glands have a high number of ACE2 receptors (Doyle et al., 2021Song et al., 2020). Furthermore, the essential role of the renin-angiotensin-aldosterone system (RAAS) in the perception of flavors has been confirmed previously. Similarly, the cases of gustatory dysfunction have been reported in patients receiving angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers in a dose-dependent manner. It has been suggested that ACE2 inhibitors inactivate the G protein-coupled proteins and sodium-ion channels located in the taste receptors. Similarly, it has been suggested that SARS-CoV-2-induced ACE2 down-regulation and the consequent RAAS impairment are associated with gustatory dysfunction in patients with COVID-19 (Luchiari et al., 2021). Also, early detection of SARS-CoV RNA in saliva before lung injury confirms that salivary glands might be the initial target for the virus.

Previously, it has been shown that the Middle East respiratory syndrome coronavirus (MERS-CoV) binds to the sialic acid receptors, the pathway that has also recently been indicated for SARS-CoV-2 (Milanetti et al., 2020Park et al., 2019). Sialic acid is a substantial factor of the salivary mucin and has protective effects on glycoproteins that transport taste molecules inside taste pores from early enzymatic metabolism (Witt and Miller, 1992). Thus, SARS-CoV-2 could block the binding sites of sialic acid on the taste buds, increasing the destruction rate of the taste molecules and cause ageusia.

As the entranceway of SARS-CoV-2 to the host cells, ACE2 receptors are also present in the oral mucosa. By binding to these receptors, inflammation and consequent cytokine signaling pathways in taste buds might affect the sense of taste. As in acute respiratory distress syndrome, this pathway could be induced through the interaction between Toll-like receptors and the virus. Also, inflammatory cytokines such as interferons can cause apoptosis and alter the turnover of taste buds (Wang et al., 2009Xu et al., 2020).Go to:

4. Potential therapeutic agents against olfactory and gustatory dysfunctions

We categorized the literature according to the American College of Cardiology/American Heart Association Clinical Practice Guidelines Recommendation Classification System (Halperin et al., 2016). This system evaluates medications based on the strength of recommendation (strong = I, IIa = moderate, IIb = weak, and III = moderately no benefit or strongly harmful) and quality of evidence (A = high quality randomized clinical trials, B-R = moderate-quality randomized clinical trial, B-NR = moderate-quality non-randomized clinical trial, C-LD = limited data, and C-EO = expert opinion). The summary of the promising agents against COVID-19-related smell and/or taste loss is shown in Table 1 and Fig. 1 .

Table 1

Categorization of the proposed medications for COVID-19 smell and taste loss.

MedicationMechanism of actionOutcomes (study design)Class of recommendation/Level of evidenceReferences
PentoxifyllinePDE inhibitorPromising results in smell loss (post-marketing surveillance study), No beneficial effects in patients with post-traumatic anosmia (case series)IIb/B-NR(Gudziol and Hummel, 2009Whitcroft et al., 2020)
CaffeinePDE inhibitor, Adenosine receptors antagonistDirect correlation between coffee consumption and smell scores in patients with Parkinson’s disease (retrospective cohort), 65 mg of caffeine showed no beneficial effects in patients with hyposmia related with upper respiratory tract infection or sinus node dysfunction (RCT)IIb/B-R(Meusel et al., 2016Siderowf et al., 2007)
TheophyllinePDE inhibitorImproved the smell and taste dysfunction caused by various diseases (two non-RCT)IIb/B-NR(Henkin et al., 20092012)
Intranasal insulinNeuroprotectiveBeneficial effects in olfactory dysfunction caused by infection (non-RCT), COVID-19 (non-RCT), and other diseases (RCT)IIa/B-R(Mohamad et al., 2021Rezaeian, 2018Schöpf et al., 2015)
StatinsNeuroprotective, anti-inflammatoryImproved anosmia in mice models (two animal studies)IIb/C-EO(Kim et al., 20102012)
MinocyclineNeuroprotectiveInhibit apoptosis of OSNs in rat models (Histological analysis)IIb/C-EOKern et al. (2004b)
ZincTrace element, growth factorReports of anosmia with intra-nasal zinc gluconate, No beneficial effects of zinc sulfate in chemotherapy-induced taste and smell loss (RCT)III/B-R(Davidson and Smith, 2010Lyckholm et al., 2012)
Intranasal vitamin AAnti-neurodegenerativeBeneficial effects in post-infectious smell dysfunction (retrospective cohort study)IIb/C-LDHummel et al. (2017)
Omega-3NeuroprotectiveBeneficial effects in olfactory loss caused by tumors (RCT)IIb/B-RYan et al. (2020)
Intranasal mometasoneAnti-inflammatoryNo beneficial effects in COVID-19 smell loss (RCT)III/B-RAbdelalim et al. (2021)
Intranasal fluticasoneAnti-inflammatoryBeneficial effects in COVID-19 smell loss (non-RCT)IIa/B-NRSingh et al. (2021)
Oral triamcinolone pasteAnti-inflammatoryBeneficial effects in COVID-19 dysgeusia (non-RCT)IIa/B-NRSingh et al. (2021)
MelatoninNeuroprotective, anti-inflammatoryInhibit apoptosis of OSNs in rat models (animal study)IIb/C-EOKoc et al. (2016)

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PDE, phosphodiesterase; RCT, randomized clinical trial.

Fig. 1

Fig. 1

The potential mechanistic pathways and treatments suggested for COVID-19-related smell loss. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters nasal epithelium, particularly with angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) receptors on sustentacular cells (SUSs). Damage to the olfactory sensory neurons (OSNs) could lead to a decrease in cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate cGMP levels, which can be inhibited by phosphodiesterase inhibitors (pentoxifylline, caffeine, and theophylline). Neuroprotective agents such as statins, minocycline, intranasal vitamin A, intranasal insulin, omega-3, and melatonin could regenerate olfactory receptor neurons (ORNs). Also, the inflammatory effects of the virus in the nasal epithelium can be blocked by corticosteroids, statins, and melatonin. BG, bowman’s gland; GC, granule cell; MC, mitral cell; MVC, microvillar cell.

4.1. Pentoxifylline (IIb/B-NR)

Signal transduction begins while an odorant binds to the receptors of an ORN. The odor-receptor complex results in the intracellular activation of type 3 adenylate cyclase by a G protein, leading to an elevated intracellular cyclic adenosine monophosphate (cAMP). An increased level of intracellular cAMP leads to calcium influx and depolarization of the neuron, consequently. Of note, it has been confirmed that in patients suffering from anosmia and ageusia, the salivary and nasal mucus growth factors, including cAMP and cyclic guanosine monophosphate (cGMP), were lower than healthy individuals (Henkin and Velicu, 20082011). In the cilia of OSNs, cAMP is metabolized by phosphodiesterase 1C2 (Henkin et al., 2007Nakamura, 2000). Pentoxifylline is a methylxanthine derivative that acts as a phosphodiesterase inhibitor. Thus, it could be reasonable to consider that pentoxifylline-induced inhibition of phosphodiesterase 1C2 can increase intracellular cAMP levels. Also, pentoxifylline reduces TNF-α and other inflammatory cytokines such as IL-1, leading to immunomodulatory effects (Hassan et al., 2014). The effect of pentoxifylline on olfactory function has been evaluated in Gudziol and Hummel’s (2009)prospective post-marketing surveillance. A total of 19 patients were included in the study. Of them, 15 patients were assigned to receive 200 mg of pentoxifylline intravenously, two times per day, and 4 patients received 200 mg of pentoxifylline orally 3 times per day. The mean (SD) of the age of patients was 51 (19.9), and 52.6% of them were female. Data analysis showed a significant reduction in odor threshold after treatment with pentoxifylline (P = 0.01). This reduction was markedly more in younger patients than in older patients (P = 0.001). However, the nasal airflow did not significantly change by pentoxifylline (P = 0.84). Of note, although the oral pentoxifylline has smaller bioavailability, of 4 patients who received the oral forms, half of them showed a clinically significant reduction in odor threshold (Gudziol and Hummel, 2009). The prospective design and small sample size of this study increase the risk of bias for accurate interpretation of these results. Furthermore, the patients in this study have diseases other than COVID-19 that led to olfactory loss. Conversely, a case series of 6 patients with post-traumatic anosmia showed that administration of oral pentoxifylline (200 mg 3 times daily for 3 weeks) did not significantly improve the odor threshold, discrimination, and identification scores (P-values = 0.3, 0.06, and 0.1, respectively) (Whitcroft et al., 2020). Due to the different results, conducting larger double-blinded clinical trials, which directly evaluate the pentoxifylline role in COVID-19 patients with olfactory or gustatory dysfunctions, is recommended.

4.2. Caffeine (IIb/B-R)

Caffeine is a CNS stimulant that belongs to the methylxanthine class. The pharmacologic effects of methylxanthine derivatives can be caused by phosphodiesterase inhibition and blocking of adenosine receptors. Particularly, caffeine could affect the CNS by antagonizing different subtypes of adenosine (A1, A2A, A2B, and A3) receptors in the brain (Ribeiro and Sebastião, 2010). Previously, it has been shown that in rodents, the genes of the adenosine A2A receptors are highly expressed in the granular cells of the accessory olfactory bulb (Abraham et al., 2010Kaelin-Lang et al., 1999Nunes and Kuner, 2015).

A study by Prediger et al. aimed to assess the efficacy of caffeine on age-related olfactory deficiency in rats. This study demonstrated that caffeine could improve olfactory dysfunction with doses of 3, 10, and 30 mg/kg through blocking A2A receptors (P = 0.001) (Prediger et al., 2005). Furthermore, cAMP and cGMP have substantial effects on olfactory function. Thus, increasing the intracellular levels of cAMP and cGMP by phosphodiesterase inhibitors with less adverse effects can be suggested as potential treatment approaches for anosmia and ageusia/dysgeusia.

Several studies have evaluated the association between caffeinated coffee consumption and various clinical outcomes. For example, a retrospective cohort on 173 patients with Parkinson’s disease (mean age = 58.1 years, 69% female) showed that higher coffee consumption significantly improved the scores of smell test with means of 30.4, 32.6, 33.1, and 34.4 for consuming <1, 1, 2 to 3, and ≥4 cups daily (P = 0.009); this improvement was more noticeable among men. Also, this study showed that the rate of hyposmia is greater among patients whose daily coffee consumption was ≤1 cup compared to patients with more than 1 cup of coffee consumption (26% versus 8%; OR = 0.026; 95% CI, 0.10, 0.67; P = 0.007) (Siderowf et al., 2007). Although these results were adjusted for some confounding factors, the study’s observational design still cannot confirm the exact role of coffee consumption on hyposmia.

A double-blinded, placebo-controlled study was carried out on 76 patients with hyposmia due to either upper respiratory tract infection (n = 48) or sinus node dysfunction (n = 26) to evaluate the effects of caffeine on olfactory dysfunction. The mean age of patients was 57 years, with a mean duration of 14 months for olfactory loss. Patients were assigned to receive 65 mg caffeine in one cup of espresso (n = 39) or a placebo (n = 38). The evaluations before and 45 min after intervention could not support the beneficial effects of coffee in patients suffering hyposmia (odor discrimination: t = 0.03, P = 0.97; odor threshold: t = 0.05, P = 0.96; discrimination and threshold combination score: t = 0.79, P = 0.83) (Meusel et al., 2016). This study only evaluates the short-term effects of coffee on olfactory dysfunction; however, the result may differ with a longer duration of coffee consumption or higher dose. Another limitation was the small sample size of the study that can increase the risk of bias. Despite several types of studies about the role of caffeine in olfactory and gustatory dysfunctions, lacking data on COVID-19 patients makes it difficult to define whether it improves anosmia or ageusia. However, coffee consumption might be a safe way to resolve these complications in patients without caffeine sensitivity.

4.3. Theophylline (IIb/B-NR)

As previously discussed, cAMP and cGMP have key roles in the normal olfactory and gustatory functions (Henkin et al., 2007). As a phosphodiesterase inhibitor, theophylline administration has been evaluated on 312 patients with smell loss. Based on the measurement prior to the study, the reason for patients’ smell loss was related to the lower levels of cAMP and cGMP in the nasal and salivary mucus. In this study, patients received 200–800 mg of theophylline orally for 2–8 months. The results showed that the administration of theophylline was associated with smell function improvement in 50.3% of patients. The doses of 600 and 800 mg showed better results than 200 or 400 mg. Therefore, high doses of oral theophylline are required to elevate cAMP and cGMP levels; however, the high doses might result in increased adverse events such as tachycardia, tremor, restlessness, and gastrointestinal disorders. Also, theophylline has a life-threatening narrow therapeutic window that needs regular blood level monitoring (Henkin et al., 2009Skinner, 1990).

Therefore, another trial evaluated the intranasal theophylline effects on 10 patients from 312 patients of the previous study; these patients were selected due to their lower than expected response for oral theophylline or experiencing adverse effects. The mean age of patients was 64 years. They had a smell or taste loss for several reasons: post-viral olfactory dysfunction, allergic rhinitis, head trauma, and congenital olfactory dysfunction. While the serum level of theophylline became unmeasurable after 3–12 weeks of the oral drug discontinuation, the intranasal theophylline was administered with a dose of 20 μg daily for 4 weeks. The improvement of smell and taste perception has occurred in 8 patients after intranasal administration, which was greater than the oral theophylline. Moreover, no adverse effects were observed after the intranasal theophylline administration (Henkin et al., 2012). However, it should be noted that this trial was primarily conducted to assess the safety of intranasal theophylline use. Thus, the studies with a larger sample size and the placebo group should evaluate the efficacy of intranasal theophylline.

4.4. Intranasal insulin (IIa/B-R)

The intranasal pathway is a well-known drug delivery system for the CNS; particularly for insulin, the mechanism of brain delivery was fully understood. In mice models, fluorescent and electron microscopy imaging of olfactory tissues showed that intranasal insulin affects the brain through the olfactory nerve pathway (Renner et al., 2012). Insulin can be involved in olfactory function through receptors presented on MCs of the olfactory bulb. Furthermore, it has neuroprotective effects and could regenerate the olfactory mucosa (Fadool et al., 2011Lacroix et al., 2011). In a study bySchopf et al. (2015), 10 patients with post-infectious olfactory loss were included to receive 20 units of insulin in each nostril (a total of 40 units). The function of the olfactory system was assessed 30 min after insulin administration. After a year from the first intervention, the patients were asked to receive 0.4 ml of intranasal saline as a placebo. The mean age of patients was 46.5 years, and the mean body mass index for them was 27.1 kg/m2. According to the measurements of olfactory functions, 60% and 28.5% of patients showed an improvement in odor threshold and sensitivity after intranasal insulin and saline administration, respectively. The intensity of the odor perception was significantly higher after insulin application than the placebo (P = 0.04). Of note, the higher body mass index resulted in significantly better odor identification after insulin administration (P < 0.01) (Schöpf et al., 2015). However, the small sample size and non-randomized design of this study limited the interpretation of results.

In a randomized clinical trial by Rezaeian (2018), the role of intranasal insulin in olfactory function has been assessed in patients with mild to severe hyposmia that lasts more than 6 months. Totally, 38 patients underwent randomization to receive either 40 units of intranasal protamine insulin (n = 19) or 20 mL of normal saline as a placebo (n = 19) two times per week for 4 weeks. The mean age of patients and the mean duration of hyposmia in the insulin and placebo groups were 37.3 versus 35.7 years and 2.3 versus 3.0 years, respectively. The mean (±SD) score of the insulin-treated group was significantly higher than the placebo group (5.0 ± 6 0.7 versus 3.8 ± 6 1.0, P = 0.01) (Rezaeian, 2018). Recently, Mohamad et al. (2021) formulated intranasal insulin films to evaluate their effectiveness in managing SARS-CoV-2 induced anosmia. Of 40 patients who underwent randomization, 20 patients were assigned to receive intranasal insulin films, and 20 were assigned to the placebo group. The comparison of the olfactory function between the two groups showed better scoring test results for the insulin-treated group regarding both odor detection (7.9 ± 1.2 versus 3 ± 0.8) and discrimination (6.7 ± 0.5 versus 2.8 ± 1). Moreover, comparing scores before and after intervention showed that, unlike the placebo group, insulin administration resulted in significantly higher scores after intervention (Mohamad et al., 2021).

4.5. Statins (IIb/C-EO)

Statins are known as 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors that are widely used in cases of hypercholesterolemia. Besides their lipid-lowering activity, they have multiple beneficial properties, including anti-inflammatory, immunomodulatory, and neuroprotective effects (Saee di Saravi et al., 2017). Previously, it has been shown that statins could improve the proliferation and neurogenesis of injured OE through immunohistochemical staining investigations. In this study, statin-treated (10 mg/kg for 4 weeks) rats showed a higher rate of OE proliferation and better regeneration of neurons than both prednisolone-treated (1 mg/kg for 2 weeks) or control groups (Kim et al., 2010). In another study on anosmia using mouse models, the improvement of the olfaction system was observed among 75% of mice with oral administration of 10 mg/kg atorvastatin versus 16.6% of control groups (P = 0.004) (Kim et al., 2012). These studies show the neuroprotective and anti-inflammatory effects of statins to improve the COVID-19 related anosmia. Of note, the adverse effects of the statins such as arthralgia and hepatotoxicity should be taken into account, and the pros and cons of treatment should be evaluated cautionary.

4.6. Minocycline (IIb/C-EO)

Minocycline belongs to the tetracycline class of antibiotics approved to manage a wide variety of infections such as skin, respiratory tract, and sexually transmitted infections. Furthermore, minocycline exerts several effects, including anti-inflammatory, anti-apoptotic, and anti-angiogenesis activities. The interference with apoptosis, particularly in neurons, makes minocycline the most neuroprotective agent among tetracycline derivatives. The beneficial effects of minocycline have been indicated in several neurodegenerative disorders such as Huntington’s disease, Parkinson’s disease, Alzheimer’s disease, and degeneration of photoreceptor cells. Besides, the beneficial effects of minocycline against olfactory dysfunction have been reported. Histological analysis of animal olfactory tissue showed that minocycline could inhibit apoptosis of OSN in rat models with bulbectomy (Kern et al., 2004b). The balance between OSN apoptosis and regeneration is vital in maintaining a normal sensory function (Kern et al., 2004a). Thus, this may be a rationale for raising the number of OSNs by inhibiting apoptosis by using well-tolerated medication minocycline.

4.7. Zinc (III/B-R)

Zinc is a trace element that contributes as one of the growth factors in taste and smell function. It has been shown that growth factors activate stem cells in both taste buds and olfactory epithelial cells. Zinc is a constituent of the salivary enzyme carbonic anhydrase VI, which plays a vital role in the maintenance of taste and smell function. Therefore, zinc deficiency could result in anosmia and dysgeusia (Komai et al., 2000Wrobel and Leopold, 2004). Also, Equils et al. (2021)suggested that a reduction of nasal zinc level is a common nasal immune reaction to acute viral infections such as SARS-CoV-2 and involves the pathogenesis of anosmia.

Moreover, they proposed that patients with zinc deficiency have long-lasting anosmia and severe COVID-19 (Equils et al., 2021;Ozlem Equils, 2020). Previously, several reports of anosmia caused by the zinc-containing nasal product (Zicam) forced the U.S. Food and Drug Administration (FDA) to recall them. Moreover, Davidson and Smith (2010) suggested that intranasal zinc gluconate can cause anosmia or hyposmia in patients (Davidson and Smith, 2010). Also, intranasal zinc sulfate (5%) is well known to induce anosmia in animal models (Cancalon, 1982McBride et al., 2003). In a double-blinded, placebo-controlled, randomized clinical trial, administration of 50 mg elemental zinc sulfate two times per day showed no significant improvements in chemotherapy-induced taste and smell dysfunctions in comparison with the placebo group. However, the small sample size (n = 58), lacked standard methods to evaluate sensory variations, and various concurrent medication used in patients increased the risk of bias in this study (Lyckholm et al., 2012).

4.8. Intranasal vitamin A (IIb/C-LD)

The active metabolite of vitamin A, retinoic acid, participates in various biological situations, including olfactory system embryogenesis, cell growth, and differentiation. Also, retinoic acid has immunomodulatory properties that might improve cell turnover and protection, mainly in the OE, which is susceptible to several inflammatory particles. Due to the regenerative and immunomodulatory effects of Vitamin A on ORNs, some studies were conducted to evaluate intranasal vitamin A effects on olfactory dysfunction (Rawson and LaMantia, 2007).

In a retrospective cohort study, 170 patients with post-infectious and post-traumatic smell complaints were treated with smell training and topical vitamin A (n = 124) or smell training alone (n = 46). Of note, patients with other causes of olfactory dysfunction such as congenital anosmia and/or aged younger than 18 years were not included in this study; the dose of intranasal vitamin A drop was 10 000 units per day for 2 months. Also, smell training was carried out for 3 months. The mean ± SD of the age of patients was 55 ± 14 years, and approximately 59% of them were female. After nearly 10 months of follow-up, the rise of smell distinction score was markedly higher in the vitamin A group than the control group (P = 0.008). In patients with post-infectious olfactory dysfunction, 37% and 23% were clinically improved in the vitamin A and control groups, respectively (P = 0.03). The comparison of the groups in the post-traumatic patients showed no significant changes in the olfactory function (P = 0.29) (Hummel et al., 2017). Although this study supported the beneficial effects of vitamin A in infection-induced olfactory dysfunction, further studies are required to directly evaluate the efficacy and safety in SARS-CoV-2 induced olfactory dysfunction. Also, the duration and the dose of vitamin A administration in this study were based on expert opinion. Moreover, the possible adverse events were not indicated in this study.

4.9. Omega-3 (IIb/B-R)

Omega-3 polyunsaturated fatty acids are vital parts of membrane phospholipids that have substantial effects on gene expression. The low levels of docosahexaenoic acid (DHA), an essential omega-3 fatty acid found in fish oil, exert signs of olfactory dysfunction (Greiner et al., 2001). A multi-institutional, prospective, randomized controlled trial has evaluated the effects of omega-3 administration on olfaction. This trial included 110 patients with sellar or parasellar tumors who underwent endoscopic resection were assigned to receive either nasal saline irrigations (n = 55) or nasal saline irrigations combined with omega-3 supplements with a total dose of 2000 mg per day (n = 55). According to the results, omega-3 administration was found to have beneficial effects on olfactory loss after controlling for multiple confounding variables (odds ratio [OR] 0.05; 95% CI 0.003–0.81; P = 0.03) (Yan et al., 2020). This study did not declare whether patients used other medications with potential benefits on olfactory function, such as corticosteroids, limiting the interpretation. Moreover, it is noteworthy that omega-3 supplements should be used with caution in patients with fish allergy, hepatic failure, and bleeding risk, particularly in patients on concomitant antiplatelet or anticoagulant medications.

4.10. Corticosteroids (mometasone: III/B-R; fluticasone: IIa/B-NR; oral triamcinolone paste: IIa/B-NR)

Corticosteroids could combat the local inflammatory response in the nasal area and taste buds, which may occur during the anosmia and ageusia caused by COVID-19. In addition, corticosteroids could directly improve the olfactory function by modifying the sodium-potassium adenosine triphosphatase (Na/K-ATPase) present on ORNs. Na/K-ATPase is also a key factor of the salivary glands, which is required for the secretion of saliva in the glandular acini, along with later alteration in the ducts (Catana et al., 2013Kim et al., 2016).

Abdelalim et al. (2021) evaluated the use of mometasone nasal spray for the treatment of COVID-19-related anosmia in a randomized clinical trial. Patients with RT-PCR confirmed COVID-19 who aged 18 years or older and experienced recent anosmia and/or ageusia entered the study. Besides, previous use of systemic steroids and pregnancy were exclusion criteria of the study. Patients in the intervention group (n = 50) received mometasone furoate nasal spray with a dose of 100 μg per day for three weeks plus olfactory training. In comparison, patients in the control group (n = 50) were managed by olfactory training alone. The median age of patients was 29.0 years, and 54% were men; mostly (94%) suffered from mild or moderate COVID-19 symptoms. The comparison of smell scores showed no significant difference between the groups after 1, 2, and 3 weeks of treatment (P = 0.10, 0.08, and 0.16, respectively). Also, the duration of anosmia was statistically similar between both groups, with the mean (SD) of 26.41 (7.99) days versus 26.15 (5.07) days for the intervention and control groups, respectively (P = 0.88) (Abdelalim et al., 2021). Although the results of this study did not support the beneficial effects of topical steroids in anosmia caused by COVID-19, the small sample size and unblinded design of the study should be taken into account in the interpretation of the results. Also, some patients received systemic steroids during the study period, which may affect the results.

Another clinical trial in COVID-19 patients assessed the efficacy of topical fluticasone and triamcinolone on anosmia and taste dysfunction, respectively. Of the 120 patients enrolled in the study, 60 patients received two puffs of fluticasone nasal spray for anosmia and triamcinolone paste three times daily for dysgeusia. On day five of the intervention, the smell and taste perceptions were significantly improved compared to the first day (Singh et al., 2021). In this study, saline irrigations or gargles were also administered that might affect the results. Also, the limited sample size and non-randomized design of the study increased the risk of bias.

4.11. Melatonin (IIb/C-EO)

Melatonin is recognized as an anti-inflammatory, antioxidative, and immune-enhancing medication with a great safety profile. Due to melatonin’s small size and amphiphilic properties, it has high cell diffusion ability and permeability through biological compartments, including the blood-brain barrier (BBB). Melatonin renovates BBB homeostasis preventing microvascular hyperpermeability and thus making it a favorable agent to combat SARS-CoV-2 induced neuroinvasion. Also, the neuroprotective effects of melatonin on OSNs were previously indicated in rat models (Koc et al., 2016Romero et al., 2020). However, more clinical data are needed to explore the role of melatonin in smell and taste loss following COVID-19.

5. Discussion

The current study has reviewed the suggested pathways for the anosmia and ageusia caused by SARS-CoV-2 infection and summarized some of the agents to treat them based on pharmacology principles. This summary can be used in designing further clinical trials in the era of COVID-19.

The anosmia and ageusia caused by SARS-CoV-2 have some important properties. First, the notable proportions of COVID-19 patients experience these symptoms that can be the only features of the disease. Second, the symptoms suddenly start and mostly persist for a short period of time. Third, mostly they are not associated with nasal congestion (Butowt and von Bartheld, 2020Lechien et al., 2020). These symptoms are not life-threatening; however, they affect the quality of life and are associated with depression, anxiety, and increased suicidal thoughts(Elkholi et al., 2021Yom-Tov et al., 2021). The precise pathophysiology of anosmia and ageusia is unclear, but several studies suggest multiple causations. Among the suggested mechanisms, direct damage in the SUSs and the local inflammation are the most likely causations for the SARS-CoV-2 induced anosmia. Previously, neuronal damage, including direct damage to ORNs is considered as the least probable reason from two reasons: first, ACE2 and TMPRSS2 are not expressed in ORNs; second, the time required for clinical recovery is faster than the regeneration of ORNs in most cases (Printza and Constantinidis, 2020). However, nasal samples and magnetic resonance imaging results showed that ORN infection and CNS invasion play a key role in COVID-19-related anosmia. The neuronal damage should be particularly taken into account in COVID-19 patients with long-lasting anosmia (Boscolo-Rizzo et al., 2020Butowt and von Bartheld, 2020de Melo et al., 2021Kandemirli et al., 2021Meinhardt et al., 2021Politi et al., 2020). Considering the correlation between olfactory and gustatory systems, the mechanistic pathways contributing to anosmia could also cause ageusia. However, some unique pathways have also been suggested for ageusia/dysgeusia. Similar to anosmia, among the suggested pathways for ageusia, the participation of the central nervous system looks less probable since the appearances of this participation, such as meningitis and encephalitis, are experienced rarely in COVID-19 (Butowt and von Bartheld, 2020Finsterer and Stollberger, 2020Luchiari et al., 2021).

Taken together, several medications have been suggested to treat anosmia and ageusia. Previously, olfactory training was recommended as an effective and safe way for olfactory dysfunction. However, there is no medication approved to treat olfactory dysfunction. Among the discussed medications, corticosteroids are the most studied in COVID-19. However, it should be noted that the use of systemic corticosteroids for the SARS-CoV-2-mediated olfactory and gustatory dysfunctions might have additional risks and could reduce the viral clearance from the body (Tlayjeh et al., 2020). Other medications mentioned in this review were mostly neuroprotective used for different causes of anosmia and/or ageusia.

Considering the involvement of the neuronal pathway in COVID-19-induced anosmia and/or ageusia, neuroprotective agents, including intranasal vitamin A, intranasal insulin, omega-3, statins, minocycline, and melatonin, might have beneficial effects in patients with long-lasting anosmia by inducing regeneration of the ORNs. Also, phosphodiesterase inhibitors can activate olfactory function through depolarization of the neurons. However, further studies are required to assess the effects of theophylline, pentoxifylline, and caffeine on SARS-CoV-2 induced anosmia and/or ageusia. Different formulations of zinc have also resulted in completely different results. Some of the zinc-containing products were recalled by the U.S. FDA since there were several cases with compliance of anosmia with them. The precise association between SARS-CoV-2 infection and zinc level, either in the systemic or in the local level, is not fully understood. There are hypotheses that low zinc levels are linked with anosmia and dysgeusia, and additional clinical trials are required for further consideration (Equils et al., 2021). Finally, the medications’ safety issues, adverse reactions, contraindications, and drug interactions, should be considered before administration.

5.1. Limitation

Our study might have some limitations. First, due to the lack of data in the era of COVID-19 mediated anosmia and/or ageusia, the proposed medications have a low level of evidence to support their application in treating anosmia and ageusia following SARS-CoV-2 infection. Second, similar to most review articles, some studies may be missed to enter our review.

6. Conclusion

We searched the literature to review the potential mechanistic pathways and treatments in COVID-19-related anosmia and/or ageusia. According to available data, there are limited studies about possible treatments of COVID-19 taste and smell loss, which need further clinical trials. This review can provide basic information to direct future clinical trials according to clinical pharmacology principles.Go to:

Author agreement

We certify that all authors have seen and approved the final version of the manuscript (EJP-59088R1) being submitted to the European Journal of Pharmacology. We warrant that the article is the authors’ original work, has not received prior publication, and is not under consideration for publication elsewhere.

Funding sources

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data statement

Declaration of competing interest

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Smell and Taste Loss Recovery Time in COVID-19 Patients and Disease Severity

Authors: Athanasia Printza,1,*Mihalis Katotomichelakis,2Konstantinos Valsamidis,1Symeon Metallidis,3Periklis Panagopoulos,4Maria Panopoulou,5Vasilis Petrakis,4 and Jannis Constantinidis1

J Clin Med. 2021 Mar; 10(5): 966.Published online 2021 Mar 2. doi: 10.3390/jcm10050966 PMCID: PMC7957474PMID: 33801170

Abstract

A significant proportion of people infected with SARS-CoV-2 report a new onset of smell or taste loss. The duration of the chemosensory impairment and predictive factors of recovery are still unclear. We aimed to investigate the prevalence, temporal course and recovery predictors in patients who suffered from varying disease severity. Consecutive adult patients diagnosed to be infected with SARS-CoV-2 via reverse-transcription–polymerase chain reaction (RT-PCR) at two coronavirus disease-2019 (COVID-19) Reference Hospitals were contacted to complete a survey reporting chemosensory loss, severity, timing and duration, nasal symptoms, smoking, allergic rhinitis, chronic rhinosinusitis, comorbidities and COVID-19 severity. In a cross-sectional study, we contacted 182 patients and 150 responded. Excluding the critically ill patients, 38% reported gustatory and 41% olfactory impairment (74% severe/anosmia). Most of the patients (88%) recovered their sense of smell by two months (median: 11.5 days; IQR: 13.3). For 23%, the olfactory loss lasted longer than a month. There were no significant differences in the prevalence and duration of chemosensory loss between groups of varying COVID-19 severity, and sexes (all p > 0.05). Moderate hyposmia resolved quicker than more severe loss (p = 0.04). Smell and taste loss are highly prevalent in COVID-19. Most patients recover fast, but nearly one out of ten have not recovered in two months.

1. Introduction

Since the coronavirus disease-2019 (COVID-19) pandemic outbreak, many studies have demonstrated that a significant proportion of people who test positive for COVID-19 have a new onset of smell or taste loss [1,2,3,4]. The Centers for Disease Control and Prevention, the World Health Organization, and National Public Health Authorities added ‘new loss of taste or smell’ to the list of symptoms related to COVID-19. The pathogenesis of anosmia related to SARS-CoV-2 has not been defined and most studies have shown that COVID-19-related olfactory dysfunction demonstrates distinct characteristics differentiating it from post-viral olfactory loss related to other viral causes [1,5]. The olfactory loss is of sudden onset, usually profound, and comes early in the disease process [3,4,6,7]. The duration of the smell and taste disorders in COVID-19 disease is still unclear. Many studies reported a quick recovery in the majority of patients [1,8,9]. However, chronic symptoms after COVID-19 disease, including persisting fatigue and loss of taste and smell, have been reported by patients even several months after the onset of the disease [10,11]. The long-term recovery and the influence of the COVID-19 severity or the chemosensory dysfunction severity on the outcome are not clear. We aimed to investigate the longer-term recovery of smell and taste loss in COVID-19 patients who suffered from varying disease severity and chemosensory impairment severity.

2. Materials and Methods

A telephone survey was conducted on consecutive adult patients diagnosed as being infected with SARS-CoV-2 at two COVID-19-Reference University Hospitals, in March and April 2020, in a cross-sectional study. All patients had been diagnosed via a reverse-transcription–polymerase chain reaction (RT–PCR). The study had ethics approval by the two institutional review boards. Three call attempts for each participant were made. All participants provided verbal consent during the interviews. Patients who were not reachable or reported that they did not recall the relevant period events were excluded. Olfactory or/and gustatory disorders before COVID-19 and cognitive disorders were also exclusion criteria. We did not collect data for the deceased patients. The patients were contacted and asked to complete a survey related to taste and smell impairment related to COVID-19 (Table 1. The telephone survey content). It included questions about impairment of smell and taste, nasal congestion, and rhinorrhea. The patients were asked to rate the severity of every symptom on an ordinal scale with the following response options: 0: no loss/absence of the symptom; 1: mild; 2: moderate; 3: severe; 4: extremely severe. The survey also included questions about the timing and duration of symptoms, smoking, history of allergic rhinitis, and chronic rhinosinusitis (CRS). Demographic characteristics (sex and age) and comorbidities were also recorded. Information on severity ratings of COVID-19 was collected from the medical records. The clinical severity of COVID-19 was defined as described by WHO [12] as mild, moderate, severe, and critical. The mild disease includes symptomatic patients meeting the case definition for COVID-19 without evidence of viral pneumonia or hypoxia, moderate patients not exhibiting signs of severe pneumonia, severe patients with clinical or radiographic signs of severe pneumonia including SpO2 < 90% on room air or respiratory rate > 30 breaths/min, and critical ICU-treated patients.

Table 1

The telephone survey content.

During Your COVID-19 Illness
1. Did you experience loss/impairment of smell?The severity in an ordinal scale 0–4
2. Did you experience loss/impairment of taste?The severity in an ordinal scale 0–4
3. Did you experience nasal congestion/obstruction?The severity in an ordinal scale 0–4
4. Did you experience rhinorrhea?The severity in an ordinal scale 0–4
5. When did you first notice the loss of smell?Before/After diagnosis
6. Did the loss/impairment of smell resolve and when?Yes ● No     Days from onset
7. Did the loss/impairment of taste resolve and when?Yes ● No     Days from onset
8. Are you smoking?Yes ● No ● Ex-smoker ● Electronic
9. Do you have a history of allergic rhinitis?Yes ● No
10. Do you have a history of chronic rhinosinusitis?Yes ● No

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Statistical Analysis

Data were analyzed with IBM SPSS Statistics for Windows version 25.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics were obtained; continuous variables are expressed as means with standard deviation, while categorical variables are presented as frequencies (percentages). The normality of the variables was ascertained with the Kolmogorov–Smirnov and Shapiro–Wilk test when the number of data was more or less than 50 respectively. Differences between not normally distributed quantitative data were assessed with the use of the Mann–Whitney U test for independent samples. For differences of qualitative parameters between groups, the Chi-square test was applied. For multiple comparisons between more than two groups of not normally distributed quantitative and qualitative variables, Kruskal–Wallis and Chi-square tests were performed, respectively. No post hoc pairwise comparisons were performed. Correlations between two categorical variables were evaluated either with the use of the Chi-square test or Fisher’s Exact test (in the case of dichotomous categorical variable), and logistic regression was applied to check associations between a categorical and a continuous variable. A p value of <0.05 was considered as the statistical significance level.

3. Results

We contacted 182 patients. Twenty-six were not reachable, five declined to participate, one had a history of hyposmia. The study cohort consisted of 150 patients (all Caucasian), with a mean age of 51.6 ± 16.8 (ranging from 18 to 89 years). The patients’ demographic and clinical characteristics are presented in Table 2.

Table 2

The patients’ demographic and clinical characteristics.

Patients, n = 150, n (%)
Age, years18–89
Mean ± SD51.6 ± 16.8
Sex
Male93 (62)
Female57 (38)
Smoking21 (14)
Allergic rhinitis11 (7)
Chronic rhinosinusitis3 (2)
Comorbidities
No medical history86 (57)
Hypertension30 (20)
Diabetes16 (11)
Cardiopathy9 (6)
Covid-19 severity
Mild56 (37)
Moderate50 (33)
Severe34 (23)
Critical (ICU-treated)10 (7)
Hospitalized94 (63)

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n: number of patients; %: percentage, SD: standard deviation.

The median time from the disease onset to the patients’ survey was 61 days (IQR:13). More than half of the participants had no other medical history (57%) while the most common comorbidities were hypertension, diabetes, and cardiac diseases. The study cohort consisted of patients who had suffered from all disease severity levels.

Olfactory and gustatory disorders were reported by 58 patients (39%) and 54 patients (36%) respectively. Forty-nine patients (33%) reported olfactory and gustatory disorders, nine isolated smell loss and five isolated taste loss. We analyzed further the chemosensory loss prevalence and characteristics in patients with mild, moderate, and severe disease, excluding ICU-treated patients (n = 10), since this small subgroup was not considered representative of the critically ill patients for reasons that we comment in the discussion. In this cohort, 41% experienced a loss of smell, which was severe or extremely severe for 74% of them and 38% taste loss (extremely severe for 61% of them) (Table 3. Chemosensory loss characteristics). One out of four patients experienced smell loss before other COVID-19 symptoms. Only a small percentage suffered from nasal blockage and rhinorrhea.

Table 3

Chemosensory loss characteristics in patients with mild, moderate, and severe COVID-19 disease.

Patients (n = 140), n (%)
Smell loss57 (41)
Taste loss53 (38)
Smell and taste loss48 (34)
Nasal obstruction16 (11)
Rhinorrhea13 (9)
Allergic rhinitis11 (8)
Chronic rhinosinusitis3 (2)
Smell loss severity
Mild3 (5)
Moderate12 (21)
Severe11 (19)
Extremely severe (anosmia)31 (54)
Taste loss severity
Mild3 (6)
Moderate11 (21)
Severe7 (5)
Extremely severe32 (61)
Smell loss recovery50 (88)
Taste loss recovery42 (79)
Hyposmia before other symptoms15 (26)
Smell loss duration (days), median (IQR)11.5 (13.3)
Taste loss duration (days), median (IQR)10 (8)

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n: number of patients; %: percentage; IQR: Interquartile Range.

Most of the patients (88%) recovered their sense of smell by 61 days. The median recovery time was 11.5 days (IQR: 13.3), (mean: 14.8 ± 11.2). In two weeks, 58% of the patients had an olfactory recovery and in a month 77%. Similarly, 42 patients (79%) recovered their sense of taste by 61 days. The median recovery time was 10 days (IQR: 8), (mean: 13.8 ± 10.6). Figure 1 shows the recovery time after the onset of smell loss.

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Figure 1

Olfactory recovery over time.

No statistically significant differences were noted in the prevalence of smell loss and taste loss and their duration between groups of varying disease severity (mild, moderate, severe), and sexes (all p > 0.05) (Table 4). The percentages of patients who recovered their sense of smell or taste in the subgroups with varying chemosensory loss severity showed no statistically significant differences (all p > 0.05) (Table 5). Patients’ groups with varying olfactory loss severity showed statistically significant differences in the days to smell loss recovery (p = 0.04). In the patients who recovered their sense of smell, patients with moderate loss had a quicker recovery compared to patients with more severe impairment. The smell loss correlated significantly with the taste loss (Chi-square test, p < 0.001), and the presence of rhinorrhea (Chi-square test, p = 0.005).

Table 4

Comparison of the prevalence and duration of hyposmia between groups of varying COVID-19 disease severity and sexes.

Smell Loss Prevalence Patients; n (%)pHyposmia Duration Days; Mean ± SDp *
COVID-19 Disease Severity0.3270.756 **
Mild
Moderate
Severe
19 (33)
23 (46)
15 (44)
13.5 ± 8.3
14.1 ± 12
16.9 ± 13.2
Sex0.3270.874 ***
Male
Female
33 (38)
24 (44)
14.1 ± 9.2
15.7 ± 13.9

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n: number; %: percentage of hyposmic patients in any disease severity or sex subgroup; SD: Standard deviation; p: comparison of hyposmia prevalence in the different subgroups, Chi-square test; p *: comparison of hyposmia duration in the different subgroups; **: Kruskal–Wallis test; ***: Mann–Whitney U test.

Table 5

Comparison of olfactory and gustatory recovery rates and chemosensory loss duration between patients’ groups with varying chemosensory loss severity.

Recovery Rates Patients; n (%)pDays to Recovery Mean ± SDp *
Smell loss severity0.3960.04
Moderate
Severe
Extremely severe
10 (83)
11 (100)
27 (87)
9 ± 6.8
21.2 ± 12.5
14.7 ± 10.3
Taste loss severity0.510.084
Moderate
Severe
Extremely severe
8 (73)
6 (85)
28 (88)
8.5 ± 7
15.8 ± 12.8
14.8 ± 10.7

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n: number; %: percentage of patients in any chemosensory severity subgroup who recovered; SD: standard deviation; p: comparison of recovery rates between groups of different chemosensory severity, Chi-square test; p *: comparison of days to recovery between groups of different chemosensory severity, Kruskal–Wallis test.

A few participants who suffered olfactory loss reported smoking, allergy, and CRS. Therefore, we did not perform a subgroup analysis regarding the olfactory recovery. Eight patients who developed smell loss were smokers, and 88% of them recovered their sense of smell in an average time of 15.4 days. Six patients with smell loss reported a history of allergic rhinitis. Five out of them (82%) recovered olfaction in 5, 5, 7, 16, and 33 days (an average time of 13.2 days). Only one patient in the subgroup of smell loss reported a history of chronic rhinosinusitis. There were no significant associations between olfactory dysfunction and age (logistic regression, p = 0.267), sex (Chi-square test, p = 0.12), smoking (Fisher Exact test, p = 0.919), disease severity (Chi-square test, p = 0.327), allergic rhinitis (Fisher Exact test, p = 0.355), chronic rhinosinusitis history (Fisher Exact test, p = 0.639) and the presence of nasal blockage (Chi-square test, p = 0.059).

4. Discussion

Our cohort exhibited a significant prevalence of smell loss, severe and of sudden onset in most cases. A large proportion of the patients recovered from their chemosensory losses in a month (77%) and even more of them (88%) in two months. A characteristic pattern of quick recovery is evident (six out of ten recovered in two weeks) as it has been reported in other studies [1,13]. However, a small proportion of patients exhibit persisting loss indicating the need to identify predictive factors for persisting hyposmia. No difference was noted in the prevalence of olfactory and gustatory disorders between mild, moderate, and severe COVID-19 disease. Previous studies indicated a greater prevalence of chemosensory deficits in outpatients compared to hospitalized patients [1,14]. It has been postulated that anosmia might be a biomarker of the magnitude of the host’s response to SARS-CoV-2 infection [14]. However, a more detailed analysis of the correlation of smell impairment with disease severity levels is limited to date. We report on a cohort of consecutive patients of all disease severity levels. We did not include the small subgroup of ICU-treated patients in further analysis, because there are serious concerns regarding the validity of self-reporting in this subgroup. The non-ICU-treated patients were representative of home- and hospital-treated patients. Only a small percentage of patients were not reached on the telephone calls, not willing to participate, or presented exclusion criteria. On the contrary, among the critically ill patients, almost half did not survive and a significant proportion of the survivors were excluded from the study because they were still suffering from serious deconditioning. The findings of other research teams are supportive of our results. Recently, a high prevalence of smell impairment (95%) was reported in assisted-breathing patients (ICU-excluded) [15]. Moein et al. also reported no significant relationship between COVID-19 severity and smell impairment in a cohort of hospitalized patients presenting a high prevalence of smell impairment [16].

The majority of our patients had severe loss of smell/anosmia, at onset (74%), in agreement with the findings reported in other studies [1,5]. Our patients’ groups with varying chemosensory loss severity showed no statistically significant differences in recovery rates. Vaira et al. also reported no significant difference in the persistence of impairment between patients with varying olfactory loss severity at baseline evaluation of their cohort [7]. However, regarding the time to recovery in those who recovered their sense of smell, in our study, patients with moderate olfactory loss had a quicker recovery compared to patients with more severe impairment. This is in agreement with findings reported by Lechien et al., who found that a less severe loss of smell was significantly associated with an earlier recovery [5]. In our study, the calculated mean duration of smell loss recovery was smaller for extremely severe than for severe loss; however, our anosmic patients did not have a quicker recovery overall. The days to recovery have been calculated and compared only for the patients who recovered their sense of smell by 61 days. Whereas all patients with severe hyposmia (100%) had recovered their sense of smell by 61 days, a percentage of anosmic patients had not recovered. Therefore, the percentage of anosmic patients who had not recovered by 61 days from smell loss onset and had olfactory impairment for longer than 61 days are not included in this comparison. Regarding individual patients results, it took four patients (out of 11) 33, 35, 36, and 45 days to recover olfaction in the severe loss subgroup and four patients (out of 27) 30, 30, 31, and 47 days in the anosmia subgroup. The main difference between these subgroups is the patients that had not recovered by 61 days. Larger studies on patients with all levels of disease severity will be needed to determine whether there are predisposing factors for developing long-lasting chemosensory disorders.

The prevalence of nasal blockage and rhinorrhea (11.4% and 9.2% respectively) was small, similar to that reported by other studies [17]. There are, though, studies that reported a much higher prevalence of nasal obstruction and rhinorrhea [18]. We found no significant association between olfactory dysfunction and the presence of nasal blockage. Altundag et al., though, reported that nasal congestion was found to be more prevalent in cases with olfactory dysfunction compared to patients without olfactory dysfunction [19]. We found that smell loss significantly correlated with taste loss and rhinorrhea. Other studies have also shown such a correlation [5]. Although the typical COVID-19-related smell impairment usually does not affect patients with significant nasal symptoms, a small percentage of patients might have a component of nasal inflammatory changes contributing to the hyposmia.

Similar to other studies, we found no associations between age, and gender and smell impairment [7]. The prevalence of allergic rhinitis, chronic rhinosinusitis, and smoking were small in our cohort and no association was found with olfactory loss. A few participants who suffered olfactory loss reported smoking, allergy, and CRS. Therefore, we did not perform a subgroup analysis regarding the olfactory recovery, but descriptive statistics suggest similar patterns of recovery in patients with allergic rhinitis and chronic rhinosinusitis with those recorded in the whole cohort of patients with smell loss. Most studies found no association of comorbidities with the persistence of olfactory dysfunction [5,7], but a recent study reported an association of comorbidities with a worse olfactory recovery in patients with allergic rhinitis, smoking, and hypertension [9].

Most of the patients in our study (88%) had recovered their sense of smell by two months, but a small proportion presents persisting hyposmia. Similar results have been reported by Lechien et al., who reported that, at two months, 80% of their cohort had achieved normal levels of olfactory function [5]. However other researchers have reported higher rates of early recovery (86% in a month after the onset of olfactory dysfunction) [17] or worse recovery [20]. Recently 6-month follow-up data were published on a cohort of patients who presented with a sudden loss of smell in March 2020 reporting persisting very severe and complete loss of smell in 11% of the patients [21]. Fatigue and smell loss were the most common symptoms in a cohort of patients questioned for long-term persistence of symptoms post COVID-19, a mean of 125 days after disease onset [22]. Our knowledge regarding SARS-CoV-2-related symptoms is evolving [23]. Another population-based study found that, in a cohort of non-hospitalized subjects contacted for reporting persistent symptoms, 65% reported a loss of smell and 69% loss of taste at diagnosis and 12% reported loss of smell and 10% loss of taste a median of 117 days from disease diagnosis [24].

A strength of our study is the inclusion of a comprehensive cohort of consecutive patients with a confirmed diagnosis of COVID-19 by two reference hospitals, therefore limiting patient selection bias related to age, residence, health-care profession, and information about COVID-19-related smell loss. Our cohort is representative of all disease severity levels. The recovery rate beyond the early four weeks recovery was measured. The chemosensory loss severity was rated at a scale that allowed us to examine the possible correlation of the olfactory and gustatory loss severity with the recovery rate and the time from chemosensory loss onset to recovery.

A limitation of our study is that the chemosensory dysfunction was not documented with olfactory and gustatory tests. Olfactory questionnaires are considered less reliable in comparison to objective tests. Vaira et al. reported that 10.3% of patients who were found to have a disorder on objective testing had self-reported normal function [7], and adversely in a prospective controlled trial that assessed with validated psychophysical tests the patients’ complaints of smell loss, 61% of COVID-19 patients reported a subjective loss in smell, whereas 54% had a positive test [25]. Self-reporting was appropriate given the retrospective type of our study. The research on COVID-19-related hyposmia relies a lot on questionnaires due to the pandemic restrictions and the short duration of the hyposmia [1]. Another limitation of the study is that patient reports are subjected to recall bias. Furthermore, there is a risk of misclassification of severity ratings when self-reporting of olfactory or gustatory function is retrospective. Recall is considered to be good for distinctive disease symptoms [26]. Smell loss is a very distinct symptom. We acknowledge that rating of symptoms’ severity retrospectively can be inaccurate, but in the context of COVID-19-related smell loss, the great majority of patients in all studies report a sudden and severe change of functional status (severe hyposmia or anosmia) [1] and this reduces the risk of inaccurate rating. Asking the patients to recall events at an order, reference to a calendar, and intervening health events can improve recall [26]. During the pandemic, being diagnosed with COVID-19 was a cardinal health event and with the anxiety of whether the mild disease would turn to more serious, a reference to a calendar of events is strong and a timeline exists for patients regarding the disease resolution. Recall reliability can increase by using precise language, and confirming that the patient is not psychologically or physically impaired [26]. Our study followed these recommendations. We developed a short, appropriate-for-telephone-use survey, using simple everyday language. Furthermore, we excluded from this study patients under rehabilitation for serious deconditioning. In studies about COVID-19-related smell loss, the most appropriate methods of data collection were applied, balancing recruitment bias, recall bias, and the research questions. Another limitation of the study is the small sample size of the subgroups of patients with different COVID-19 severity levels and chemosensory loss. Similarly, the sample sizes of the subgroups of patients with different chemosensory loss severity are small. Differences in the recovery might be detectable in larger participants’ groups.

Smell and taste loss is highly prevalent in COVID-19 of all levels of severity. Most patients recover fast, but one out of ten have not recovered in two months. The recovery rates up to two months do not correlate with the COVID-19 and chemosensory loss severity. The time from chemosensory loss to recovery for the patients who recover is associated with the severity of impairment. Less severe hyposmia tends to resolve quicker.Go to:

Acknowledgments

The authors thank Anastasia Nikolaidou, Chatzi Souleiman Ipek, and Maria Zisoglou for assistance with data collection.Go to:

Author Contributions

Conceptualization, A.P. and J.C.; methodology, A.P. and M.K.; formal analysis, K.V.; investigation, A.P., S.M., P.P., V.P., M.P. and M.K.; data curation, A.P., K.V. and M.K.; writing—original draft preparation, A.P.; writing—review and editing, A.P., M.K., K.V., S.M., P.P., V.P., M.P. and J.C.; supervision: A.P.; project administration: A.P. All authors have read and agreed to the published version of the manuscript.Go to:

Funding

This research received no external funding.Go to:

Institutional Review Board Statement

The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board of two COVID-19 Reference University Hospitals in Greece: Scientific Board of AHEPA University Hospital, Thessaloniki, decision: SB10/347/8.5.2020, and Scientific Board of University Hospital of Alexandroupolis, decision: SB8/9/18065/12.06.2020/25.06.2020).Go to:

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.Go to:

Data Availability Statement

Data are available upon request from the authors.Go to:

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Coronavirus and the Nervous System

What is SARS-CoV-2 and COVID-19?

Coronaviruses are common causes of usually mild to moderate upper respiratory tract illnesses like the common cold, with symptoms that may include runny nose, fever, sore throat, cough, or a general feeling of being ill. However, a new coronavirus called Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) emerged and spread to cause the COVID-19 pandemic.

COVID-19, which means Coronavirus disease 2019, is an infectious disease that can affect people of all ages in many ways. It is most dangerous when the virus spreads from the upper respiratory tract into the lungs to cause viral pneumonia and lung damage leading to Acute Respiratory Distress Syndrome (ARDS). When severe, this impairs the body’s ability to maintain critical levels of oxygen in the blood stream—which can cause multiple body systems to fail and can be fatal.

What do we know about the effects of SARS-CoV-2 and COVID-19 on the nervous system?

Much of the research to date has focused on the acute infection and saving lives. These strategies have included preventing infection with vaccines, treating COVID-19 symptoms with medicines or antibodies, and reducing complications in infected individuals.

Research shows the many neurological symptoms of COVID-19 are likely a result of the body’s widespread immune response to infection rather than the virus directly infecting the brain or nervous system. In some people, the SARS-CoV-2 infection causes an overreactive response of the immune system which can also damage body systems. Changes in the immune system have been seen in studies of the cerebrospinal fluid, which bathes the brain, in people who have been infected by SARS-CoV-2. This includes the presence of antibodies—proteins made by the immune system to fight the virus—that may also react with the nervous system. Although still under intense investigation, there is no evidence of widespread viral infection in the brain. Scientists are still learning how the virus affects the brain and other organs in the long-term. Research is just beginning to focus on the role of autoimmune reactions and other changes that cause the set of symptoms that some people experience after their initial recovery. It is unknown if injury to the nervous system or other body organs cause lingering effects that will resolve over time, or whether COVID-19 infection sets up a more persistent or even chronic disorder.

What are the immediate (acute) effects of SARS-CoV-2 and COVID-19 on the brain?

Most people infected with SARS-CoV-2 virus will have no or mild to moderate symptoms associated with the brain or nervous system. However, most individuals hospitalized due to the virus do have symptoms related to the brain or nervous system, most commonly including muscle aches, headaches, dizziness, and altered taste and smell. Some people with COVID-19 either initially have, or develop in the hospital, a dramatic state of confusion called delirium. Although rare, COVID-19 can cause seizures or major strokes. Muscular weakness, nerve injury, and pain syndromes are common in people who require intensive care during infections. There are also very rare reports of conditions that develop after SARS-CoV-2 infection, as they sometimes do with other types of infections. These disorders of inflammation in the nervous system include Guillain-Barré syndrome (which affects nerves), transverse myelitis (which affects the spinal cord), and acute necrotizing leukoencephalopathy (which affects the brain).

Bleeding in the brain, weakened blood vessels, and blood clots in acute infection

The SARS-CoV-2 virus attaches to a specific molecule (called a receptor) on the surface of cells in the body. This molecule is concentrated in the lung cells but is also present on certain cells that line blood vessels in the body. The infection causes some arteries and veins—including those in the brain—to  become thin, weaken, and leak. Breaks in small blood vessels have caused bleeding in the brain (so-called microbleeds) in some people with COVID-19 infection. Studies in people who have died due to COVID-19 infection show leaky blood vessels in different areas of the brain that allow water and a host of other molecules as well as blood cells that are normally excluded from the brain to move from the blood stream into the brain. This leak, as well as the resulting inflammation around blood vessels, can cause multiple small areas of damage. COVID-19 also causes blood cells to clump and form clots in arteries and veins throughout the body. These blockages reduce or block the flow of blood, oxygen, and nutrients that cells need to function and can lead to a stroke or heart attack.

stroke is a sudden interruption of continuous blood flow to the brain. A stroke occurs either when a blood vessel in the brain becomes blocked or narrowed or when a blood vessel bursts and spills blood into the brain. Strokes can damage brain cells and cause permanent disability. The blood clots and vascular (relating to the veins, capillaries, and arteries in the body) damage from COVID-19 can cause strokes even in young healthy adults who do not have the common risk factors for stroke.

COVID-19 can cause blood clots in other parts of the body, too. A blood clot in or near the heart can cause a heart attack. A heart attack orInflammation in the heart, called myocarditis, can causeheart failure, and reduce the flow of blood to other parts of the body. A blood clot in the lungs can impair breathing and cause pain. Blood clots also can damage the kidneys and other organs.

Low levels of oxygen in the body (called hypoxia) can permanently damage the brain and other vital organs in the body. Some hospitalized individuals require artificial ventilation on respirators. To avoid chest movements that oppose use of the ventilator it may be necessary to temporarily “paralyze” the person and use anesthetic drugs to put the individual to sleep. Some individuals with severe hypoxia require artificial means of bringing oxygen into their blood stream, a technique called extra corporeal membrane oxygenation (ECMO). Hypoxia combined with these intensive care unit measure generally cause cognitive disorders that show slow recovery.

Diagnostic imaging of some people who have had COVID-19 show changes in the brain’s white matter that contains the long nerve fibers, or “wires,” over which information flows from one brain region to another. These changes may be due to a lack of oxygen in the brain, the inflammatory immune system response to the virus, injury to blood vessels, or leaky blood vessels. This “diffuse white matter disease” might contribute to cognitive difficulties in people with COVID-19. Diffuse white matter disease is not uncommon in individuals requiring intensive hospital care but it not clear if it also occurs in those with mild to moderate severity of COVID-19 illness.

For More Information: https://www.ninds.nih.gov/Current-Research/Coronavirus-and-NINDS/nervous-system