Olfactory Dysfunction in Patients With Coronavirus Disease 2019: A Review

Abstract

The coronavirus disease 2019 (COVID-19) pandemic is wreaking havoc on public-health and economic systems worldwide. Among the several neurological symptoms of patients with COVID-19 reported in clinical practice, olfactory dysfunction (OD) is the most common. OD occurs as the earliest or the only clinical manifestation in some patients. Increasing research attention has focused on OD, which is listed as one of the main diagnostic symptoms of severe acute respiratory syndrome-coronavirus-2 infection. Multiple clinical and basic-science studies on COVID-19-induced OD are underway to clarify the underlying mechanism of action. In this review, we summarize the clinical characteristics, mechanisms, evaluation methods, prognosis, and treatment options of COVID-19-induced OD. In this way, we hope to improve the understanding of COVID-19-induced OD to aid early identification and precise intervention.

Keywords: COVID-19; clinical characteristics; mechanism; olfactory dysfunction; treatment.

Figure 1

Potential mechanisms of coronavirus disease 2019 (COVID-19)-induced olfactory dysfunction. (i) COVID-19 directly affects sustentacular (SUS) cells through interactions with the ACE2 receptor, thereby leading to abnormal transmission of odor molecules. (ii) Injury to SUS cells, horizontal basal cells (HBCs) as well as the release of cytokines and proinflammatory factors in the systemic and local nasal epithelium lead to abnormal function of olfactory sensory neurons (OSNs). (iii) Olfactory-bulb vascular pericytes, glial-cell injury, and release of cytokines and proinflammatory factors into the systemic and local brain trigger abnormalities in functions of the olfactory bulb and limbic system of the brain.