Calvarial Syphilitic Osteomyelitis as a Rare Manifestation of Secondary Syphilis in an Immunocompetent Patient: A Rare Diagnostic Challenge.

Syphilitic osteomyelitis of the skull is a rare manifestation of syphilis, typically associated with tertiary or congenital stages, and is exceptionally uncommon during secondary syphilis. We report the case of a 27-year-old immunocompetent, HIV-negative male who presented with persistent headaches and localized frontal scalp tenderness. Magnetic resonance imaging (MRI) revealed two calvarial lesions with adjacent soft tissue and meningeal enhancement. Serological testing confirmed secondary syphilis, while other sexually transmitted infections, including HIV, hepatitis B/C, Neisseria gonorrhoeae, and Chlamydia trachomati s, were excluded. Despite normal cerebrospinal fluid (CSF) findings, Venereal Disease Research Laboratory (VDRL) testing and HIV polymerase chain reaction (PCR) assays on CSF were not performed due to financial limitations. The patient was treated with a 14-day course of ceftriaxone, leading to complete symptom resolution and radiologic improvement. This case highlights the importance of including syphilitic osteomyelitis in the differential diagnosis of atypical cranial lesions, particularly in at-risk patients. It emphasizes the diagnostic value of MRI in such presentations.