Colonoscopic appearances are normal or near normal. As the changes are often patchy, an examination limited to the rectum may miss cases of<unk> , and so a full colonoscopy is necessary. Multiple colonic biopsies are taken in order to make the diagnosis. Histological features of colonic biopsies indicating<unk>  are: greater than 20 intraepithelial lymphocytes per 100 epithelial cells and, additionally, 10-20 μm of a thickened subepithelial collagen band in collagenous colitis. Inflammation of the lamina propria, with mainly mononuclear cells, may be observed in collagenous colitis. Pathology<unk>  is characterized by an increase in inflammatory cells, particularly lymphocytes, in colonic biopsies with an otherwise normal appearance and architecture of the colon. Inflammatory cells are increased both in the surface epithelium ("intraepithelial lymphocytes") and in the lamina propria. The key feature is more than 20 intra-epithelial lymphocytes per 100 epithelial cells. These are the principal features of lymphocytic colitis. An additional distinguishing feature of collagenous colitis is a thickened subepithelial collagen layer, which may be up to 30 micrometres thick, that occurs in addition to the features found in lymphocytic colitis. The fact that the two types of<unk>  share many features including epidemiology, risk factors and, response to therapy has led to the suggestion that they are actually subtypes of the same disease. Differential diagnosis Differential diagnoses, which should be ruled out, include bile acid diarrhea, lactose malabsorption, celiac disease, Crohn's disease, ulcerative colitis, and infectious colitis.
Microscopic colitis
Bile acid malabsorption
Collagenous colitis
Coeliac disease
Lymphocytic colitis
Crohn's disease
Cytomegalovirus colitis
Lactose intolerance