Bell's palsy as the first manifestation of neurosyphilis in an immunocompetent and HIV-negative patient: a challenging diagnosis.

Acute isolated peripheral facial nerve palsy is mainly idiopathic. In a minority of cases, however, it may result from other disorders that complicate the diagnostic process. Atypical clinical features, temporal evolution, and associated signs or symptoms are crucial in guiding diagnostic suspicion. In this case, we discuss a 57-year-old woman with acute unilateral facial weakness. The clinical course, together with the combination of imaging and laboratory studies, ultimately led to the final diagnosis of neurosiphilis. In the antibiotic era, the number of patients with the classic form of neurosphilis has decreased, while the frequency of subtle and atypical forms has increased so that neurosyphilis may occur without prior evidence or manifestation of infection [1–3]. When one or more cranial nerves are affected in the absence of meningeal signs or fever, the diagnosis can be particularly challenging given the wide range of differential diagnoses of cranial multineuropathies [4]. This case emphasizes the role of clinical reasoning in addressing atypical presentations of common neurological syndromes.