The atypical colitides

Collagenous colitis and lymphocytic colitis are 2 atypical forms of inflammatory bowel disease that are relatively uncommon. Patients with these disorders usually present with chronic nonbloody, watery diarrhea. The diagnosis is based on specific histopathologic findings from colonic biopsy specimens. Given the relatively uncommon occurrence of these conditions, much about them still is unknown. This article outlines the current understanding of these atypical colitides and highlights advances in research and treatment. The first reported case of collagenous colitis was described in 1976 [39]. The patient, a middle-aged woman, presented with chronic watery diarrhea and was found to have a thickened subepithelial collagen band on colonic biopsy. Based on histologic similarity to collagenous sprue, the new disease entity was termed collagenous colitis. Subsequently the term microscopic colitis was introduced in a report of patients with chronic watery diarrhea, normal endoscopy, and a colonic biopsy specimen showing colitis without the distinctive collagen band [49]. In 1989, this disease was renamed lymphocytic colitis [37], and the term microscopic colitis was broadened to encompass all patients with histologic evidence of colitis and normal endoscopy. Given the similar presentations and histopathology of collagenous and lymphocytic colitis, it remains unresolved whether these colitides represent 2 ends of a disease spectrum or if they are separate entities.