Smell and taste disorders in COVID-19: From pathogenesis to clinical features and outcomes

Abstract

Patients with COVID-19 often complain of smell and taste disorders (STD). STD emerge early in the course of the disease, seem to be more common in SARS-CoV-2 infection than in other upper respiratory tract infections, and could in some cases persist for long after resolution of respiratory symptoms. Current evidence suggests that STD probably result from a loss of function of olfactory sensory neurons and taste buds, mainly caused by infection, inflammation, and subsequent dysfunction of supporting non-neuronal cells in the mucosa. However, the possible occurrence of other mechanisms leading to chemosensory dysfunction has also been hypothesized, and contrasting data have been reported regarding the direct infection of sensory neurons by SARS-CoV-2. In this mini-review, we summarize the currently available literature on pathogenesis, clinical manifestations, diagnosis, and outcomes of STD in COVID-19 and discuss possible future directions of research on this topic.

Keywords: Ageusia; Anosmia; COVID-19.

Fig. 1

Possible pathogenesis of olfactory disorders in COVID-19. Olfactory disorders in COVID-19 may results from: 1) Infection and damage of supporting cells of the olfactory epithelium, leading to inflammation and alterations in local homeostasis; 2) Infection or immune-mediated damage of endothelial cells and vascular pericytes, leading to hypoperfusion and inflammation. In both cases, recruitment of inflammatory cells, cytokine release and generation of neurotoxic compounds may indirectly influence the neuronal signaling. Olfactory cleft obstruction and possibly direct infection of neuronal cells may also occur. (Created with Biorender.com).