• Subepithelial eosinophilic accelular fibrotic change(arrow)

• Overlying epithelium is flattened and irregular with focal lymphocytic infiltrates and some degenerative change

• Moderate increase in lymphocytes within the lamina propria

• The crypts are intact but show some lymphocytic infiltrate without crypt degeneration

•Unknown

•Unknown. However, three unproven postulates have been suggested: an autoimmune process; a primary inflammatory process to a yet unknown pathogen; and an acquired defect in collagen metabolism.

•There is a predominance of middle aged females(mean 54 yrs.)

•The major and sometimes only symptom is profuse watery diarrhea

•In addition vague abdominal pain, nausea and mild weight loss may be present

•In spite of the impressive degree of diarrhea, patients are usually in good health

•There is an increased occurrence of associated autoimmune diseases such as rheumatoid arthritis, autoimmune thyroiditis, scleroderma, and uveitis

•The condition is often chronic

•The colon mucosa is usually normal but may show some evidence of edema and erythema

•The pathognomonic lesion is is thickening of the subepithelial collagen layer (SCL)

•The SCL has a mean thickening of 15.0 um vs. a normal SCL of 2.5 um

•The SCL in collagenous colitis is least thickened in the rectum

•The surface epithelium usually show a variable patchy lymphocytic infiltrate with variable degenerative changes which include loss of mucin, flattening, karyorrhexis and lifting of the surface epithelium

•The crypts may contain intrapithelial lymphocytes but show no degenerative changes

•The lamina propria has increased lymphocytes and mononuclear cells but these are too non-specific to be useful as a diagnostic criteria

•Chronic Colitis with Thickening of the Subepithelial Collagen Layer, Jessurun, J. et al, Human Pathology:18 839-848, 1987

• Sleisenger MH, Fordtran JS. Gastrointestinal disease. 5th ed. Philadelphia: Saunders, 1993, pp. 1563-1565

• Current literature from PubMed at National Library of Medicine