Petaloid dermatosis affecting the scalp and genitalia

Abstract

A 41-year-old-male presented with a 1-month history of pruritic lesions on his scalp, neck, and penis. He had attempted a 2-week course of terbinafi ne cream, with no improvement. The lesions were unaffected by exposure to sunlight. The patient also reported new-onset wrist stiffness and pain. He had been diagnosed with primary syphilis 9 months prior to presentation, with a reactive plasma reagin titer of 1:64, and had been treated with intramuscular penicillin G benzathine 2.4 million units.Physical examination revealed annular and petaloid plaques with central clearing and raised borders on the scalp, right mandibular angle (Figure 1), and penis (Figure 2). No lesions were observed on the oral mucosa, palms, or soles. No lymphadenopathy or new-onset alopecia was present.Clinically, the differential diagnosis included discoid lupus erythematosus, lichen planus, tinea infection, sarcoidosis, and annular secondary syphilis. Serology for human immunodefi ciency virus was nonreactive, and cutaneous punch biopsy of the mandibular lesion was performed. Histologic sections revealed