Collagenous colitis in a Japanese patient.

A case of collagenous colitis is reported. A 48 year old female who had been complaining of mild diarrhea had been under medication for a gastric ulcer. Colonoscopy revealed almost normal appearance of the colonic mucosa except for one hyperplastic polyp of the cecum. Specimens of the ascending, transverse and descending colon showed a distinctively thickened collagen band beneath the surface epithelium, 10-20 microns thick, which was irregularly distributed, even within the same specimen. In some areas, the thickened collagen band was found around the upper part of the pits. Periodic acid-Schiff (PAS), Azan staining and silver impregnation were positive for this thickened collagen band. Immunohistochemically, the thickened collagen band was weakly positive for collagen type III, but negative for collagen types I and IV. Plasma cells, lymphocytes and eosinophils were observed in the lamina propria in addition to intraepithelial lymphocytic infiltration. Capillaries were increased in the thickened collagen band. The arrangement of surface epithelial cells was irregular. Crypts were not distorted. Edema, diffuse or extensive fibrosis and congestion were not found. Through these findings the patient was diagnosed as having collagenous colitis. Many cases of this had been reported in western countries, but very few in Japan. The Japanese literature was reviewed for cases of collagenous colitis and it was found that only two cases had been presented.