Case Report: A case of secondary syphilis with clinical manifestations resembling granuloma annulare.

Syphilis is caused by Treponema pallidum and progresses through different clinical stages, with a wide range of clinical manifestations. We report a case of secondary syphilis in which the patient presented with diffuse granuloma annulare-like lesions involving the neck, chest, abdomen, back, and upper extremities. Clinically, the lesions manifested as annular plaques with raised erythematous borders, accompanied by central ulceration and necrosis. The diagnosis of secondary syphilis was confirmed by skin biopsy and serological examination. Following treatment with benzathine penicillin G, the non-treponemal test (TRUST) became negative 7 months after therapy. The patient responded well to intravenous penicillin treatment, highlighting the importance of early detection and timely therapy in managing syphilis with atypical histopathological features. In recent years, the incidence of syphilis has continued to increase, underscoring the importance of recognizing this clinicopathological presentation. Routine syphilis screening is essential for accurate diagnosis and appropriate treatment.