Collagenous colitis: a cause of chronic diarrhea.

Collagenous colitis should be added to the differential diagnosis of chronic, watery, nonbloody diarrhea with normal endoscopic findings. Patients with collagenous colitis are often middle-aged women previously diagnosed as having irritable bowel syndrome. The diagnosis of collagenous colitis is based on histologic evaluation of a rectal biopsy specimen. Biopsy shows a thickened, subepithelial, acellular, eosinophilic collagen band. Symptoms often resolve after treatment with oral sulfasalazine.