Facial Nerve Palsy With Olfactory and Gustatory Dysfunction Following COVID-19 Infection: An Illustrative Case-Based Narrative Review.

COVID-19 infection has been recognized to induce a wide range of neurological manifestations, ranging in severity from transient, benign manifestations to severe neurological deficits. Cranial nerve involvement, particularly facial, olfactory, and gustatory nerve dysfunction, has emerged as a notable clinical feature in affected individuals. This review article aims to present and analyze three confirmed COVID-19 diagnoses that exhibited facial nerve palsy (FNP), olfactory disturbances (OD), and/or gustatory disturbances (GD), while also exploring the potential underlying pathophysiological mechanisms of these symptoms. This article presents three cases of laboratory-confirmed COVID-19 in which patients developed FNP along with OD and/or GD, and discusses their potential pathophysiological mechanisms. All three patients had hallmark signs and symptoms of FNP, with dysgeusia present in three and anosmia present in two. COVID-19 was confirmed with reverse transcription polymerase chain reaction (RT-PCR) testing. Neuroimaging and cerebrospinal fluid analysis ruled out other differential diagnostic possibilities. Treatment strategies varied from case to case and included steroids, antivirals, and traditional medicine. Outcomes ranged from partial to complete recovery of FNP within four weeks. The three presented cases suggest a temporal association between COVID-19 and FNP, though case reports alone cannot establish causation. While direct neural invasion, immune response, or ischemic injury are potential mechanisms, a definitive cause has not yet been established. OD and GD in the presented cases were short-lived, which may suggest, but cannot confirm, a mechanism different from direct cranial nerve involvement. This remains speculative given the small sample size. Further research is warranted to elucidate the pathophysiology of cranial nerve involvement, thereby guiding diagnosis and treatment strategies.