Secondary syphilis masquerading as lupus vulgaris in an HIV-infected patient: A diagnosis suggested by histology

We report a case of secondary syphilis mimicking lupus vulgaris in an HIV-infected patient. A 21-year-old Brazilian man presented with a two-month history of asymptomatic cutaneous lesions accompanied by fever and fatigue. Dermatological evaluation revealed an erythematous, crusted, large plaque on the neck with the 'apple jelly' sign on diascopy and two smaller scaly elements on the trunk and left palm. Bacteriological examinations for bacteria and mycobacteria gave negative results. Histology revealed psoriasiform epidermal hyperplasia and dermal lymphoplasmacytic infiltrate. Serology for syphilis was positive, and immunohistochemistry confirmed the presence of Treponema pallidum in lesional skin. A diagnosis of secondary syphilis was made, and the patient was successfully treated with benzathine penicillin G. Cutaneous manifestations of secondary syphilis are protean and skin tuberculosis may be considered in the differential diagnosis, especially in HIV-infected patients. In the current case, clinical examination, and particularly, 'apple jelly' sign positivity, was suggestive of lupus vulgaris, but only typical histopathology and immunohistochemistry led to the correct diagnosis of secondary syphilis.