PURPOSE OF REVIEW: Olfactory dysfunction (OD) can be a single and early prominent symptom of severe acute respiratory syndrome (SARS) -COV-2 infection unlike middle east respiratory syndrome (MERS) and SARS . OD data are very informative but many are not peer-reviewed, often inconclusive and may reveal variable and sometimes contradictory results . This is often due to incongruent data of subjective and objective OD testing . Mechanistic pathways of OD and taste dysfunction (TD) are slowly unveiling, not infrequently extrapolated from historical models of SARS and MERS and are still partly unclear .
RECENT FINDINGS: We reviewed the literature on OD and TD during the COVID-19 pandemic analyzing current data on pathogenesis and clinical correlates including prevalence, recovery rates, risk factors, and predictive power . Also, we evaluated various methods of subjective and objective olfactory testing and discussed challenges in management of patients with OD and rhinitis during the pandemic .
SUMMARY: Subjective evaluation of smell disturbances during COVID-19 pandemic likely underestimates true prevalence, severity, and recovery rates of OD when compared to objective testing . OD is predictive of COVID-19 infection, more so when associated with TD . Recognizing inherent limitations of both subjective and objective OD and TD testing enables us better to manage chemosensory dysfunction in COVID-19 patients . Besides, current mechanistic data suggest neurotropism of COVID-19 for olfactory neuro-epithelium and a potential role of transient receptor potential (TRP) channels . Future studies are needed to explore further the neurogenic inflammation in COVID-19.