Diversion Colitis

Diversion colitis is non-specific inflammation of the colon or rectum that is excluded from the faecal stream by an ileostomy or colostomy. It is related to loss of luminal short chain fatty acids.

Endoscopic and histological changes occur in nearly all patients within 3 to 36 months of diversion, but only a minority are symptomatic. It appears more often after diversion for inflammatory bowel disease.

Pathophysiology.

Colonocytes use butyrate from bacterial fermentation as their main fuel. Without it, the mucosa becomes atrophic and inflamed, with lymphoid hyperplasia, mucosal injury and loss of mucus.

Changes in the microbiota, nutrition and immunity contribute.

Mucus or blood stained discharge from the rectum, tenesmus, rectal pain, passage of blood, abdominal cramps and, rarely, stricture or perforation.

Red flags.

• Heavy bleeding.
• Perforation or fever.
• Stricture or new mass.

Endoscopy of the diverted segment shows erythema, friability, granularity, nodular lymphoid hyperplasia, aphthae and ulcers, with sparing of the non-diverted bowel. Biopsy shows lymphoid follicular hyperplasia, crypt abscesses and architectural distortion. Exclude infection and recurrence of Crohn disease or ulcerative colitis, which can look the same.

Differential diagnosis.

• Recurrent ulcerative colitis or Crohn disease.
• Infective proctitis (Clostridioides difficile, cytomegalovirus, chlamydia).
• Ischaemic proctitis.
• Radiation proctitis.
• Malignancy.

Restoring intestinal continuity is the definitive treatment and resolves inflammation in months. When continuity cannot be restored, give local therapy.

• Mesalazine enema: 1 g in 100 mL rectally once daily at night; 4 to 8 weeks; maximum 1 g daily as enema; monitor renal function; avoid in salicylate allergy; use caution when eGFR is under 30 mL/min.
• Mesalazine suppository: 1 g rectally once daily at night; 4 to 8 weeks; maximum 1 g daily; monitor renal function; same adjustment.
• Hydrocortisone rectal foam or enema (when mesalazine fails): 100 mg in 60 mL rectally once daily at night for 2 to 3 weeks; maximum 3 weeks; monitor for adrenal suppression with prolonged use; avoid in untreated infection.
• Short chain fatty acid enema (limited evidence): 60 to 100 mL rectally twice daily for 2 to 6 weeks; monitor symptoms; no maximum established; no renal adjustment.

Treat strictures by dilation or resection. Where the rectum remains defunctioned for years, consider resection of the diverted segment.

Monitoring. Symptoms at 4 to 8 weeks; endoscopy before reversal and after reconstruction in inflammatory bowel disease, with surveillance for dysplasia where indicated.

Referral and escalation. Colorectal surgery for restoration of continuity or resection; gastroenterology for inflammatory bowel disease.