Case 1 A 40 year old HIV-positive man who has sex with men (MSM) man presented with diarrhoea, rectal discomfort and frank rectal bleeding. Colonoscopy revealed an ulcerating mass in the proximal sigmoid and three other rectal lesions. Biopsy demonstrated inflammatory tissue only with no evidence of malignancy. At an HIV clinic review treponemal serology indicated active syphilis.
Case 2 A 50 year old HIV-negative MSM presented with a short history of rectal bleeding, change in bowel habit and tenesmus. There was a family history of colorectal cancer. Colonoscopy revealed multiple polypoid lesions with central ulceration. Biopsy demonstrated severe inflammatory cell infiltrates with no evidence of malignancy. By chance, the patient presented himself for a sexual health which revealed positive treponemal serology.
The chance identification of positive syphilis serology prompted repeat analysis of histological specimens which proved their treponemal origin. Syphilis treatment resulted in resolution of all bowel lesions in both patients at follow-up endoscopy.
Discussion: Syphilis should be considered inl patients, particularly MSM, who present with symptoms suggesting colorectal cancer. Clinicians must have a high index of suspicion with regard to diagnosing syphilis. Specific staining techniques or PCR are required to confirm the diagnosis; this may be missed if syphilis is not considered in the differential diagnosis. Sexual history, with rigorous attention to the time course of symptoms, should help to guide investigations and staging of syphilis.