The role of syphilis in exacerbating axial spondyloarthritis symptoms: A case report on diagnosis and management.

Syphilis, caused by Treponema pallidum, is resurging globally, with diverse clinical manifestations. While musculoskeletal involvement is recognised, its role in exacerbating axial spondyloarthritis (ax-SpA) or causing infectious spondylitis is poorly understood. We report the case of a 48-year-old man with long-standing ax-SpA who experienced spontaneous remission until a severe flare triggered by primary syphilis, characterised by an ulcerative lesion on the upper lip. Imaging studies revealed ankylosis of the sacroiliac joints and new inflammatory changes in the lumbar spine. Specifically, plain radiography demonstrated complete ankylosis of the sacroiliac joints, while magnetic resonance imaging revealed bone contrast enhancement, consistent with active inflammation. Syphilis infection was confirmed both serologically and by immunohistochemical staining of tissue samples. Targeted antibiotic therapy with penicillin G and amoxicillin-probenecid led to significant clinical and radiological improvement. This case highlights syphilis as a potential trigger for ax-SpA exacerbation or an infectious spinal process. Recognising syphilis in patients with unexplained axial inflammation can prevent unnecessary immunosuppressive therapy and guide effective management. With the rising incidence of syphilis, prompt diagnosis and treatment are critical for preventing spinal pathology progression and improving outcomes.