Olfactory Loss of Function as a Possible Symptom of COVID-19

To the Editor There is increasing interest in the cause of anosmia in patients with coronavirus disease 2019 (COVID-19), and the article written by Dr Eliezer et al,¹ presents an interesting finding of a patient with bilateral obstruction of the olfactory clefts. This is different from another report of a COVID-19 patient with isolated anosmia whose magnetic resonance imaging results showed normal olfactory bulb and no corresponding inflammation in the olfactory clefts or paranasal sinuses.²

Gene studies have shown that 2 key entry genes for severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) are expressed in olfactory sustentacular cells instead of olfactory sensory neurons of human olfactory epithelium.³ The same report, however, also showed that these 2 receptors were more commonly found in respiratory epithelium than in olfactory epithelium, which may support an initial obstructive cause for anosmia in SARS-CoV-2 infection, followed by possible infection of olfactory epithelium. Studies describing the natural course of olfactory disturbances in patients with COVID-19 have suggested that most patients experience recovery from olfactory disturbance within the first 2 weeks of recovery from infection, which is in contrast to the longer lasting anosmia that is expected if olfactory epithelium is damaged.⁴

In the article by Eliezer et al,¹ the patient does not have any nasal obstructive symptoms, but we note that the 3 scan images provided show presence of mild mucosal thickening in the paranasal sinuses. Opacification of the olfactory cleft can be seen concomitantly with paranasal sinus inflammation,⁵ which is not uncommon in the general population. In other words, this finding is not specific in the presence of paranasal sinus changes.

In a tertiary hospital in Singapore, we have come across a few patients with COVID-19 with or without known anosmia, whose olfactory recesses and upper half of the paranasal sinuses included in a CT scan are completely clear (Figure). In this case, the patient with anosmia did not have nasal blockage or rhinorrhea.

Figure.  Computed Tomographic Images

View LargeDownload

Computed tomographic images of a patient with COVID-19 with anosmia, hypogeusia, and no obstructive symptoms. The olfactory clefts (white and yellow arrowheads) are completely patent in this patient.

We acknowledge that the authors do not claim that opacification of the olfactory clefts is the cause for the patient’s anosmia; rather it is an observation made of a patient who has COVID-19. The purpose of this letter is to highlight that this finding is not common to all patients with COVID-19. Understanding the pathogenesis of SARS-CoV-2 causing anosmia is important, and we call for a comprehensive study, which can account for confounders, to help us understand this disease better.

Corresponding Author: Si Wei Kheok, MBBS, Department of Diagnostic Radiology, Singapore General Hospital, Block 2, Level 1, Outram Road, Singapore 169608 (kheok.si.wei@singhealth.com.sg).

Published Online: July 16, 2020. doi:10.1001/jamaoto.2020.1590

Correction: This article was corrected on August 13, 2020, to fix an error in the name of the second author in the byline. This article was corrected online.

Conflict of Interest Disclosures: None reported.