A Case of Perianal Annular Rash: Atypical Presentation of Recurrent Secondary Syphilis.

Syphilis is a complex, systemic infectious disease caused by Treponema pallidum subspecies pallidum. Secondary syphilitic lesions typically manifest within 3 months following initial exposure to T. pallidum. The predominant cutaneous manifestations of secondary syphilis are macula and papule. Certain individuals with syphilis may present with an atypical rash during the secondary stage owing to immunosuppression and other factors. Herein, we report a rare case of atypical recurrent secondary syphilis around the anus in a 65-year-old woman. Based on cerebrospinal fluid findings and skin biopsy results, the patient was ultimately diagnosed as neurosyphilis and recurrent secondary syphilis. Following intravenous antibiotic therapy, the patient's rash improved significantly. This case underscores the importance for physicians to remain vigilant regarding the possibility of syphilis when encountering cases exhibiting unusual clinical manifestations, as a definitive diagnosis necessitates a comprehensive evaluation.