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Microscopic colitis

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Microscopic colitis: an idiopathic inflammatory disease of the colon characterized by chronic, nonbloody, watery diarrhea, normal macroscopic appearance of the bowel on colonoscopy, and collagenous or lymphocytic infiltrates on microscopy

Epidemiology & Risk Factors

  • Prevents primarily in older females (F:M ratio ~ 4:1, typical age >60).
  • Smoking is a strong independent risk factor.
  • Highly associated with certain medications:
    • NSAIDs
    • PPIs (e.g., lansoprazole)
    • SSRIs (e.g., sertraline)
    • Ranitidine, ticlopidine, acarbose.
  • Strong association with autoimmune conditions (e.g., celiac disease, thyroiditis, DM1, RA).

Clinical Features

  • Chronic, watery, non-bloody diarrhea (often >4 weeks, up to 10-15 episodes/day). c
  • Nocturnal diarrhea and fecal urgency. c
  • Crampy abdominal pain, fatigue, and mild weight loss.
  • Physical exam is typically unremarkable; gross colonoscopy mucosal appearance is entirely normal.

Diagnosis

  • Initial: Stool studies (to rule out infectious etiologies, C. diff, parasites).
  • Confirmatory/Gold Standard: Colonoscopy with random biopsies of the colon (even if mucosa appears completely normal on gross inspection).
  • Key Histopathology:
    • Collagenous colitis: Thickened subepithelial collagen band (>10 μm).
    • Lymphocytic colitis: Increased intraepithelial lymphocytes (>20 per 100 epithelial cells) with normal collagen band.
  • Key Labs: Normal inflammatory markers (ESR/CRP) or only mildly elevated; normal hemoglobin and albumin.

Differential Diagnostics

  • Irritable Bowel Syndrome with Diarrhea (IBS-D): Diff by absence of nocturnal diarrhea, absence of weight loss, younger age at onset, and normal colonic biopsy. c
  • Celiac Disease: Diff by positive serology (tTG-IgA), systemic malabsorption signs, and villous atrophy/crypt hyperplasia on duodenal biopsy rather than colonic biopsy. (Note: often co-exists with MC; if budesonide fails, screen for celiac).
  • Inflammatory Bowel Disease (IBD - UC/Crohn’s): Diff by presence of hematochezia, gross endoscopic abnormalities (e.g., cobblestoning, continuous ulceration, pseudopolyps), and systemic features (fever, high inflammatory markers).
  • Bile Acid Malabsorption: Diff by clinical history (e.g., prior cholecystectomy, terminal ileal resection) and positive response to bile acid sequestrants without characteristic biopsy findings of MC.

Management

  1. Initial: Discontinue offending triggers (stop NSAIDs, PPIs, and smoking).
  2. Mild Symptoms: Anti-diarrheal therapy with loperamide or diphenoxylate/atropine.
  3. Moderate-to-Severe (First-line medical): Oral Budesonide (preferred steroid due to high first-pass hepatic metabolism, minimizing systemic glucocorticoid adverse effects).
  4. Refractory:
    • Bile acid sequestrants (e.g., cholestyramine).
    • Anti-TNF therapy (e.g., adalimumab, infliximab) or surgery (e.g., diverting ileostomy) in extremely rare, severe cases.

Complications

  • Dehydration and electrolyte imbalances (hypokalemia).
  • Substantial weight loss and malnutrition in severe cases.
  • Note: Does not increase the risk of colorectal cancer (CRC) or progression to IBD.

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