Collagenous Colitis

Collagenous colitis is the subtype of microscopic colitis defined by a thickened subepithelial collagen band on colonic biopsy.

• Collagen band over 10 micrometres thick beneath the surface epithelium, with chronic lamina propria inflammation and surface epithelial damage.
• Mean age of onset is about 65 years, with a female to male ratio of 4 to 5:1.
• Associated with NSAIDs, PPIs, smoking, autoimmune disease and celiac disease.
• Collagen thickness does not predict severity.
• Complications: dehydration, electrolyte disturbance, rare colonic perforation after colonoscopy.

• Chronic watery diarrhoea (nocturnal in many), urgency and incontinence, cramping abdominal pain, weight loss.
• Fatigue and arthralgia are common.
• Symptoms may wax and wane with spontaneous remission in 10 to 30%.
• Look for coexisting autoimmune disease (thyroid, celiac, rheumatoid arthritis).

• Colonoscopy with biopsies from the right and left colon, although the mucosa is usually normal. Rare mucosal tears (cat scar, mucosal fractures) occur.
• Histology confirms the band thickness, often most prominent in the transverse and right colon (rectal biopsies alone can miss up to 40%).
• Exclude infection, celiac disease (tTG IgA), thyroid disease, medication effect, bile acid diarrhoea, and Crohn disease.
• Faecal calprotectin is normal or mildly elevated.

• Stop NSAIDs, PPIs and other suspected drugs where feasible, and stop smoking.
• Budesonide 9 mg daily for 8 weeks is first line (response about 80%, strong evidence), then taper.
• Maintenance budesonide 6 mg daily (or 3 mg daily) for patients who relapse after stopping, up to 12 months or longer if needed.
• Alternatives: bismuth subsalicylate 262 mg three times daily, mesalazine 3 g daily (less effective), cholestyramine 4 g daily for bile acid diarrhoea.
• Refractory disease: azathioprine 2 mg/kg, methotrexate, adalimumab or vedolizumab.
• Symptomatic: loperamide 2 mg up to four times daily, rehydration.
• Monitor bone density and glucose during prolonged corticosteroid exposure. Follow up yearly.