Microscopic Colitis

Microscopic colitis is a chronic inflammatory disorder of the colon that classically presents with non-bloody, watery diarrhea, often with nocturnal symptoms, weight loss, and incontinence. It is most common in middle-aged and older women and is increasingly recognized — incidence has risen with broader awareness and routine random biopsies.

The defining feature is normal-to-near-normal endoscopic appearance with characteristic histology on biopsy. Two classic subtypes are recognized: lymphocytic colitis (≥20 intraepithelial lymphocytes per 100 epithelial cells) and collagenous colitis (subepithelial collagen band thicker than 10 µm). A third "incomplete" form has features of both. Diagnosis therefore requires biopsy from multiple colonic segments, even when the colonoscopy is grossly normal.

Common triggers include NSAIDs, proton pump inhibitors, SSRIs, and statins; bile-acid malabsorption coexists in a substantial subset. Treatment is stepwise: trigger withdrawal, antidiarrheals, budesonide (the most effective therapy in randomized trials), and bile-acid sequestrants. Refractory disease is uncommon but may need immunomodulators or biologics.