Unusual presentation of secondary syphilis mimicking erythema multiforme in HIV positive patient: a case report

Secondary syphilis is known as "The Great Imitator". It can mimic numerous diseases clinically and histologically, including erythema multiforme (EM). Coinfection with HIV often makes its manifestations more atypical leading to delays in diagnosis and therapy. A 34-year-old male-sex-male patient who had received coronavirus disease 2019 (COVID-19) vaccine 1 week earlier presented with complaints of slightly pruritic scaly erythematous targetoid plaques and erythematous macules on the trunk and extremities for 6 weeks. Histopathology examination showed basal cell vacuolar degeneration of the epidermis and lymphocytic infiltrates along the dermal-epidermal junction and superficial dermis, consistent with EM. Upon further investigation, syphilis and HIV serology were reactive (VDRL 1: 128, TPHA 1: 40960, CD4+ 461 cells/µl). Lesions improved significantly after a single dose of 2,4-million units of benzathine penicillin intramuscular injection. Secondary syphilis presenting as erythema multiforme (EM)-like eruptions is very rare. Physicians should be aware of this unusual presentation to prevent complications.