Collagenous colitis

Collagenous colitis is a type of microscopic colitis. It has a characteristic clinical presentation and no apparent endoscopic changes.

General

Presentation:

• Chronic diarrhea, non-bloody.

• Collagenous colitis may be related to lymphocytic colitis.
  • It is hypothesized that these conditions may be the same pathology at different time points.

Notes:

• Clinical DDx includes irritable bowel syndrome - which has no or subtle histopathologic changes.

Epidemiology

• Age: a disease of adults - usually 50s.
• Sex:
  • LC males ~= females,
  • CC females:males = 20:1.
• Drugs are associated with LC and CC.
  • NSAIDs - posulated association/weak association,
  • SSRIs (used primarily for depression) - moderate association, dependent on specific drug.
• Associated with autoimmune disorders - celiac disease, diabetes mellitus, thyroid disorders and arthritis.
• No increased risk of colorectal carcinoma.

Treatment

• Sometimes just follow-up.
• Steroids - budesonide -- short-term treatment.

Gross

• Endoscopic examination is normal.
  • This is why it is called a microscopic colitis.

Microscopic

Features:

• Intraepithelial lymphocytes - important.
• Collagenous material in the lamina propria (pink on H&E) -- key feature.
  • Can be demonstrated with a trichrome stain -- collagen = green on trichrome.
  • Subepithelial collagen needs to be >= 10 micrometres thick for diagnosis.
    • 8 micrometres is the diameter of a RBC.
    • The normal thickness of the subepithelial collagen is 3 micrometres.
    • Transverse colon usually thickest - in one series ~ 47 micrometres on average.
  • Thickening is usually patchy.
  • Thickening "follows the crypts from the surface" - useful for differentiating from tangential sections of the basement membrane.
  • Collagen may envelope capillaries - useful to discern from basement membrane.

Notes:

• CC is typically more prominent in the proximal colon - may reflect concentration gradient of offending causitive agents.
• Significant negative findings:
  • No PMNs.
  • No crypt distortion.
• Thickened collagen band uncommon in rectum.

Images

• 

  CC - intermed mag. (WC/Nephron)

• 

  CC - high mag. (WC/Nephron)

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TRANSVERSE COLON, BIOPSY:
- COLLAGENOUS COLITIS.

Micro

The sections show colonic mucosa with abundant intraepithelial lymphocytes (>20 lymphocytes/100 surface epithelial cells). A prominent collagen band is apparent below the epithelium (>10 micrometres thick). The glandular architecture is within normal limits.

There are no granulomas. No neutrophilic cryptitis is apparent. The epithelium matures appropriately to the surface.

See also

• Colon.
• Lymphocytic colitis.