What are the causes of transverse colitis in men who have sex with men?

Causes of Proctocolitis in Men Who Have Sex with Men

In men who have sex with men (MSM) presenting with colitis extending beyond the rectum (proctocolitis), the primary sexually transmitted causes are Campylobacter species, Shigella species, Entamoeba histolytica, and lymphogranuloma venereum (LGV) serovars of Chlamydia trachomatis 1.

Primary Sexually Transmitted Pathogens

The CDC STD Treatment Guidelines clearly distinguish proctocolitis from isolated proctitis based on anatomic extent. Proctocolitis involves inflammation extending >12 cm above the anus with associated diarrhea and abdominal cramping, differentiating it from proctitis which affects only the distal 10-12 cm 1.

Key Causative Organisms:

Bacterial Pathogens:

• Campylobacter species - Well-documented sexual transmission in MSM networks 1, 2
• Shigella species - Particularly antimicrobial-resistant strains transmitted sexually 1, 2
• LGV serovars (L1-L3) of Chlamydia trachomatis - Increasingly recognized cause of severe proctocolitis in MSM, can mimic inflammatory bowel disease and even present as bowel obstruction 1, 3

Parasitic Pathogens:

• Entamoeba histolytica - Second leading cause of death from parasitic diseases globally; increasing prevalence in MSM who engage in oral-anal contact 1, 4
• Giardia lamblia - Robust evidence for sexual transmission in MSM networks 2

Transmission Routes and Risk Factors

Proctocolitis in MSM is acquired through:

• Receptive anal intercourse 1
• Oral-anal contact (rimming) 1, 5
• Digital-anal contact 5

Specific risk factors identified include:

• Condomless anal sex 6
• Multiple or non-regular sexual partners 6
• Fisting 6
• Living with HIV, particularly with CD4 count <200 cells/μL 1, 6, 7
• Concomitant sexually transmitted infections 6, 8

Special Considerations in HIV-Positive MSM

In immunosuppressed HIV-infected patients, additional opportunistic pathogens must be considered 1:

• Cytomegalovirus (CMV)
• Mycobacterium avium complex
• Cryptosporidium
• Microsporidium
• Isospora

Critical Diagnostic Pitfall

A major clinical trap is mistaking sexually transmitted proctocolitis for inflammatory bowel disease (IBD). The histologic triad that distinguishes STI colitis from IBD includes: (1) minimal active chronic crypt-centric damage, (2) lack of mucosal eosinophilia, and (3) submucosal plasma cells with endothelial swelling and perivascular plasma cells 7. LGV proctocolitis can be particularly deceptive, mimicking Crohn's disease or even causing small bowel obstruction requiring surgical exploration 3.

Asymptomatic Carriage

Importantly, 14/30 (47%) of MSM with gastrointestinal infections in one study were asymptomatic, including those with Shigella and Campylobacter 8. This asymptomatic carriage likely facilitates ongoing sexual transmission within MSM networks.

Clinical Approach

When evaluating MSM with proctocolitis symptoms:

1. Obtain sexual history - Despite its importance, 87.2% of patients are not asked about anal intercourse during diagnostic evaluations 9

2. Perform anoscopy or sigmoidoscopy to assess extent of inflammation 1

3. Test specifically for:

   • Rectal Chlamydia trachomatis (with LGV typing if positive) 1, 3
   • Gonorrhea 1
   • Stool culture for Campylobacter, Shigella, Salmonella 1
   • Stool examination for parasites (E. histolytica, Giardia) 1, 4
   • Consider intestinal spirochaetosis (Brachyspira species) in appropriate clinical context 6

4. In HIV-positive patients with low CD4 counts, expand testing to include opportunistic pathogens 1

The key is recognizing that standard IBD workup is insufficient in MSM populations - specific STI testing and detailed sexual history are mandatory to avoid misdiagnosis and inappropriate long-term immunosuppression for presumed IBD 7, 9.