Secondary Syphilis With Concomitant Bullous Pemphigoid: A Case Report.

A 52-year-old woman presented with a three-month history of pruritic scaly palmoplantar eruptions that progressed to tense bullae over trunk and extremities along with genital mucosal involvement. Serology confirmed syphilis (VDRL reactive at 1:16 and TPHA positive), and biopsy with direct immunofluorescence (DIF) established bullous pemphigoid (BP). Treatment with benzathine penicillin led to resolution of palmoplantar and genital lesions, but there was no improvement of bullous lesions. Treatment with oral doxycycline and prednisolone significantly resolved the bullous eruptions. In adults, secondary syphilis can rarely be present as bullous eruptions, which may mimic autoimmune blistering disorders like BP, thereby posing a diagnostic dilemma. This case uniquely demonstrates BP persisting despite successful syphilis treatment (8-fold VDRL decrease), requiring ongoing immunosuppression. Unlike previously reported cases where bullous lesions resolved with antibiotics alone, this differential response confirms that syphilis can trigger independent, self-sustaining autoimmune bullous disease.