A 44-year-old male with a history of recent high-risk sexual exposure presented to the Gastroenterology clinic reporting constipation of four months' duration and distal rectorrhagia. A diagnostic colonoscopy was performed, which revealed multiple nonspecific, circular, non-elevated, whitish lesions (2-3 mm in diameter) in the last two centimeters of the rectum, suggestive of infectious proctitis (Images 1-3). Histopathological analysis identified interstitial spirochetosis, and Mycobacterium avium was concurrently isolated in the microbiological specimen.

The patient was also assessed by Dermatology due to a generalized cutaneous rash, oral ulcers and the aforementioned symptomatology. PCR testing on the rectal ulcer sample confirmed Lymphogranuloma Venereum (LGV) due to Chlamydia trachomatis serovars L1-L3. Furthermore, PCR analysis of an oral ulcer sample yielded positive results for Treponema pallidum. Based on the strong suspicion of both oral and rectal luetic secondary disease, the patient received treatment consisting of Benzathine Penicillin G 2.4 million units IM and a 3-week course of Doxycycline for the management of lymphogranuloma venereum. This regimen resulted in an adequate serological response and favorable clinical evolution. A follow-up rectoscopy is scheduled to definitively exclude the persistence of the associated Mycobacterium avium infection and its indication to be treated.

Syphilitic proctitis—an uncommon manifestation of secondary syphilis—along with LGV proctitis (secondary to C. trachomatis L1-L3 serovars) both constitute infrequent causes of proctitis. Nevertheless, their incidence has demonstrably risen over the past decades, particularly within high-risk sexual cohorts (accounting for up to 23% and 47% of proctitis cases in men who have sex with men (MSM), a subgroup where LGV is the most prevalent cause of proctitis) and in patients co-infected with HIV. Clinical presentation is often asymptomatic or may mimic Inflammatory Bowel Disease (IBD) or colorectal carcinoma, frequently featuring nonspecific endoscopic findings. This mandates a high index of clinical suspicion, a rigorous differential diagnosis, serological assays, and the meticulous collection of biopsies and microbiological samples for definitive detection. Complete clinical and endoscopic resolution is typically achieved following appropriate antimicrobial therapy. Failure to treat can lead to severe complications, including progression to proctocolitis, strictures, fibrosis, fistula or abscess formation, or even colonic perforation.

It is paramount to systematically include syphilis and lymphogranuloma venereum in the differential diagnosis of proctitis, particularly within high-risk patient populations, in order to prevent misdiagnosis and mitigate the risk of subsequent morbidities.