Atypical Skin Rash in Seronegative Secondary Syphilis.

A 26-year-old HIV-infected man presented with fever and disseminated maculopapular rash not involving his palms and soles. He had started antiretroviral therapy (ART) with an abacavir-based regimen three days prior. Although he tested negative for HLA-B*5701, the antiretrovirals were suspected to be the offending agent associated with the drug eruption. Within several days after discontinuing the ART, his clinical symptoms resided, but a skin rash accompanied by a small ulcer remained on his back (Picture 1). Skin biopsy demonstrated lymphocyte infiltration into the dermis on hematoxylin and eosin staining and Treponema pallidum on immunohistochemical staining (Picture 2). His syphilis serological titer was negative, and a prozone phenomenon was excluded. Based on the pathological evidence, penicillin was initiated, leading to a dramatic clinical response. Two months later, his Treponema pallidum Latex Agglutination test seroconverted. Physicians need to be aware of the possibility of seronegative secondary syphilis, especially in HIV-infected patients, and skin biopsy should be conducted for refractory skin lesions (1). In addition, a polymerase chain reaction test with sufficient sensitivity and specificity may facilitate the diagnosis of syphilis (2).

Picture 1.

Picture 2.