Collagenous colitis as a cause of chronic diarrhea.

Collagenous colitis should be considered in the differential diagnosis of chronic diarrheal syndromes. Colonoscopy or sigmoidoscopy in such patients should include biopsy of the mucosa proximal to the rectum, even though the mucosa appears grossly normal. Some patients have associated autoimmune disease, but the etiology of collagenous colitis is unclear. Microscopic colitis has been observed to precede collagenous colitis in some patients. Treatment with antimotility agents, sulfasalazine, oral 5-ASA compounds or corticosteroids may be effective in reducing symptoms.