Highlighting a Potential Pitfall: Positive Treponema pallidum Immunohistochemical Stain in a Patient Without Syphilis.

The Treponema pallidum antibody immunohistochemical (IHC) stain has improved our ability to detect the organism histologically. We present a case of a man with genital condyloma acuminatum with a positive T. pallidum IHC stain but negative T. pallidum serologies and no syphilitic symptoms. It has been shown that the T. pallidum antibody IHC can cross-react, staining other spirochetes, including Borrelia burgdorferi and the Brachyspira family of intestinal spirochetes. Because of the proximity of our patient's lesions to the anus, and the persistently negative T. pallidum serologies, we believe nontreponemal spirochetes colonized the condyloma, giving a false-positive T. pallidum IHC. This cross-reactivity is a potential diagnostic pitfall and is important for the dermatopathologist to recognize, thereby avoiding false diagnosis of syphilis.