A 20-year-old male, with a history of well-controlled HIV infection (undetectable viral load), presented with a 3-month history of 6 erythematous, annular, asymptomatic plaques, with well-defined, raised borders, located on the shaft of the penis and scrotum (Fig. 1). There were no other mucocutaneous lesions. Locoregional lymph nodes were not palpable.
Skin biopsy demonstrated mild acanthosis of the epidermis and a dense, band-like infiltrate composed by numerous plasma cells, in the superficial dermis, suggestive of secondary syphilis. Treponema pallidum hemagglutination assay and rapid plasma reagin (RPR) test were reactive, the later at a dilution of 1:64. The lesions completely disappeared and RPR titer reduced to 1:16, after one dose of intramuscular benzathine penicillin 2.4 million units.
Annular lesions are an unusual presentation of secondary syphilis, that may be solitary or multiple, and range from macules to mildly raised lesions to verrucous plaques. They often involve the scalp, face (namely nasolabial folds and angle of the mouth), palms, soles or genital region. However, few cases of localized annular syphilis occurring exclusively in the genital area have been described. It should be distinguished from other entities such as granuloma annulare, annular psoriasis, annular lichen planus and dermatophytosis. Histopathologic examination and serologic tests play an important role in the distinction of these different entities.
