From zoster to polyneuropathy: manifestations, mechanisms, and differential diagnosis of cranial nerve involvement in Ramsay Hunt Syndrome

Ramsay Hunt Syndrome (RHS) arises from reactivation of varicella-zoster virus (VZV) in the geniculate ganglion, clinically manifesting as facial palsy and an auricular rash. Involvement of cranial nerves (CN) beyond the facial nerve (CN VII) occurs in up to half of cases, complicating the clinical presentation. Current knowledge regarding polycranial involvement in RHS remains fragmented, largely drawn from isolated case reports and small series. This review synthesizes available evidence on the epidemiology, clinical spectrum, differential diagnosis, and mechanisms of cranial nerve involvement in RHS. Due to anatomical proximity, the vestibulocochlear nerve (CN VIII) is most frequently affected. Involvement of other cranial nerves-including the trigeminal (CN V), glossopharyngeal/vagus (CN IX/X), ocular motor nerves (CN III, IV, VI), and rarely the accessory (CN XI) or hypoglossal (CN XII) nerves-whether isolated or combined, typically reflects more extensive disease and is associated with a poorer prognosis. Advanced age, immunocompromised status, and delayed initiation of antiviral and corticosteroid therapy further influence clinical outcomes. Pathogenesis involves both direct axonal and hematogenous spread of VZV, likely accompanied by immune- and inflammatory-mediated injury. The diversity of polycranial presentations necessitates careful differential diagnosis. Future efforts should focus on elucidating molecular mechanisms, optimizing therapeutic regimens, and developing more effective rehabilitation strategies.