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Collagenous colitis is characterized by chronic watery diarrhea, radiological and endoscopic appearance are normal, but microscopic examination reveals abnormalities in the colon. The specific histopathological feature is the presence of a subepithelial collagen band (10 mm or more) adjacent to the basal membrane, together with epithelial lymphocyte infiltration and chronic inflammation of the lamina propria. A mean annual incidence of 0.6 to 6.1 per 100,000 inhabitants has been described, with a peak incidence in older women. The etiology and pathogenesis of collagenous colitis are unknown. A mechanism based on genetic predisposition, with some features of autoimmunity initiated by a noxious agent(s) in the fecal stream, which would induce dysfunction of signal transmission between surface epithelium and subepithelial myofibroblasts generating abnormalities in collagen synthesis and/or degradation, has been suggested. The overall prognosis of the disease is good because cases with life-threatening diarrhea are extremely rare, and diarrhea subsides in almost all patients either spontaneously (near 20%) or with adequate therapy. Recent randomised placebo-controlled trials suggest that budesonide is an effective treatment for collagenous colitis, inducing a short-term clinical response in 57 to 87% of patients. However, relapse usually occurs rapidly after stopping the treatment, and thus maintenance therapy with low doses of budesonide is often required. Uncontrolled studies suggest that either mesalazine, cholestyramine, or bismuth subsalicylate are also effective. |