A Case of Facial Nerve Palsy As the Initial Presentation of Early Neurosyphilis: A Diagnostic Challenge.

Neurosyphilis remains a diagnostic challenge, particularly when it presents with cranial neuropathies that mimic more common conditions such as Bell's palsy, underscoring the need for heightened clinical awareness amid the global resurgence of syphilis, especially among men who have sex with men (MSM). We report the case of a 40-year-old, previously healthy man who presented with acute-onset left peripheral facial nerve palsy, initially treated as Bell's palsy with corticosteroids; however, subtle neurological findings and limited improvement prompted further evaluation. Serologic testing revealed a new diagnosis of syphilis, cerebrospinal fluid analysis confirmed neurosyphilis, and brain MRI demonstrated characteristic facial nerve enhancement. The patient showed rapid clinical improvement following treatment with intravenous penicillin G, though his course was complicated by a Jarisch-Herxheimer reaction. This case emphasizes the importance of considering neurosyphilis in the differential diagnosis of cranial neuropathies, particularly in at-risk populations, as early recognition and appropriate antimicrobial therapy are vital for optimal neurological outcomes.