"Anosmia" the mysterious collateral damage of COVID-19

Abstract

COVID-19 pandemic spreads worldwide, with more than 100 million positive cases and more than 2 million deaths. From the beginning of the COVID-19 pandemic, several otolaryngologists described many cases of a sudden loss of smell (anosmia) associated with the disease with or without additional symptoms. Anosmia is often the first and sometimes the only sign in the asymptomatic carriers of COVID-19. Still, this disorder is underestimated, and it is not life-threatening. However, it significantly decreases the quality of life. This olfactory dysfunction continues in several cases even after the nasopharyngeal swab was negative. The occurrence of anosmia can be used as a screening tool for COVID-19 patients and can be used to identify these patients to accomplish the isolation and tracking procedures. In this review, we highlighted the possible mechanisms of anosmia in COVID-19 patients, major pathologies and features of anosmia, implications of anosmia in early diagnosis of COVID-19, evaluation of the smell function during COVID-19, and management and treatment options of COVID-19 anosmia.

Keywords: Anosmia; COVID-19; Diagnosis; Features; Implications; Mechanisms.

Fig. 1

General scheme of the five possible mechanisms that illustrate how the SARS-Cov-2 virus may cause anosmia (adapted from Butowt and Bartheld 2021). (1) SARS-Cov2 causes a damage of ORN; (2) the virus causes a damage of sustentacular cells; (3) damage of the mitral cell in the olfactory bulb of the brain may also comprise the transmission of odor sensation. (4) Utilization of Zn by the virus prevents its utilization by carbonic anhydrase which is a critical enzyme to maintain the smell function. (5) Following the infection, nasal obstruction caused by increased mucous may prevent the smell stimulus from reaching ORN

Fig. 2

Flow chart for management and treatment options of COVID-19 anosmia (adapted from Walker et al. 2020)