Increased fluid secretion by intestinal epithelium plays an important role in the pathogenesis of diarrhea in collagenous colitis. Crypt distortion is typically not seen in collagenous colitis. Histologic findings in lymphocytic colitis are similar to those in collagenous colitis, except that the subepithelial collagen band is not present. Cryptitis is a feature typical of ulcerative colitis and rarely if ever seen in collagenous colitis. Bloody discharge from anus or mucous fistula in patients with bypassed segments of colon is not a typical finding of diversion colitis 9.
Collagenous colitis affects primarily middle aged men and presents with bloody mucous diarrhea.
Nodularity and aphthous erosions and inflammatory polyps in a diverted segment of colon should raise the possibility of Crohn's disease, as these findings are atypical for diversion colitis. Yield of diagnosis in collagenous colitis is increased by targeting endoscopic biopsies to abnormal looking mucosa 12. Female predominance is not seen in lymphocytic colitis. Histologic features of diversion colitis are very similar to inflammatory bowel disease, however, maintenance of normal crypt architecture is a relatively constant feature of diversion colitis.