Track: Case Reports

Abstract:

Syphilis may adopt an annular plaque morphology, creating a striking clinical resemblance to granuloma annulare (GA). We report an unusual case with this presentation. A 57-year-old man with well-controlled HIV on Biktarvy and a remote history of Kaposi sarcoma presented with annular, scaly plaques on the right upper extremity and foot—clinically suggestive of GA. Punch biopsy of the right forearm showed lichenoid and granulomatous inflammation with a dense upper dermal perivascular and periadnexal lymphocytic infiltrate, focal spongiosis, and neutrophil exocytosis. PAS, GMS, and AFB stains were negative. Although the clinical presentation was unusual, given this histopathologic pattern, Treponema pallidum immunostaining was performed, revealing rare spirochetes. Serologic testing confirmed syphilis with positive Treponema pallidum antibodies and Rapid Plasma Reagin (RPR). This case underscores the breadth of syphilis’ clinical spectrum and the potential for infectious diseases to mimic common inflammatory dermatoses. In immunocompromised patients, syphilis should remain in the differential diagnosis of annular plaques. Ancillary testing, including treponema immunostaining, is a valuable diagnostic tool when histology is nonspecific but clinical suspicion remains. Prompt recognition allows for appropriate antimicrobial therapy and prevention of disease progression.

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William Lewis