Rectal mass caused by Treponema pallidum: confirmation by immunofluorescent staining

A 37-yr-old homosexual man presented with mild anorectal symptoms, a diffuse maculopapular rash, constitutional symptoms, and a reactive serologic test for syphilis. Sigmoidoscopy revealed a 2 x 2-cm indurated rectal mass 5 cm above the anal verge. Darkfield examination of rectal exudate revealed motile treponemes and rectal biopsy of the mass showed diffuse infiltration of plasma cells and lymphocytes. Large numbers of spirochetes were present on silver stain of the rectal biopsy specimen and these were shown to be Treponema pallidum by indirect immunofluorescence. The rectal mass and symptoms resolved following penicillin therapy. This case and a review of previously reported cases of anorectal syphilis emphasize the significance of these often neglected and misdiagnosed lesions of syphilis.