Chronic colitis with thickening of the subepithelial collagen layer (collagenous colitis): histopathologic findings in 15 patients.

The histopathologic features of collagenous colitis were studied in 14 women and one man. All but one patient presented with chronic watery diarrhea: 10 had a history of thyroid disease or unspecified arthritis. All 15 patients showed characteristic thickening of the subepithelial collagen layer (SCL) in colorectal biopsy specimens, but in the distal colorectum the thickening was sometimes absent or borderline. Patchy or diffuse injury to the surface epithelium was seen in all cases and was independent of SCL thickening. The injured surface epithelium was infiltrated by lymphocytes and variably by eosinophils and neutrophils, causing it to resemble the surface epithelial injury seen in the small intestine in celiac disease. Crypts were commonly infiltrated by lymphocytes but without associated epithelial injury. The lamina propria in all patients was expanded by lymphocytes, plasma cells, and eosinophils. Neutrophilic cryptitis was seen in seven patients but was usually sparse. Watery diarrhea abated in eight patients treated with corticosteroids or sulfasalazine and was often paralleled by restoration of surface epithelium, reduction in surface epithelial lymphocytes, diminished SCL thickening, and reduced lamina propria eosinophils. Therapy did not consistently alter other inflammatory changes. The possible role of autoimmunity in collagenous colitis should be investigated because of the following circumstantial evidence: the overwhelming female predominance; the frequent presence of possible immunologically mediated disorders such as thyroid and joint disease; the resemblance of surface epithelial changes to those in celiac disease; and the response to corticosteroids.