Microscopic colitis. A review.

J Dig Dis. 2013 Jun;14(6):277-81.

Brown WR, Tayal S.

Department of Medicine, Denver Health Medical Center and University of Colorado School of Medicine, Denver, Colorado, USA. imesmeded@gmail.com


Microscopic colitis (MC) is characterized by a triad of watery diarrhea, usually normal colonoscopic findings and typical microscopic findings. Two distinct histological forms of MC have been defined: lymphocytic colitis and collagenous colitis, but overlapping features may be present. The incidence of MC appears to be rising and in some countries it may account for as many as 10-20% of patients with non-bloody watery diarrhea. The cause of MC remains unknown and is likely to be multifactorial. The pathogenesis is poorly defined, and numerous immunological abnormalities have been reported. MC is commonly associated with autoimmune diseases including celiac disease. Use of various medications, most notably non-steroidal anti-inflammatory agents and proton pump inhibitors, have been etiologically implicated but not firmly established as causative. In imperfect trials several agents have been reported to be effective in the treatment of MC; budesonide is the best studied and evidence supporting its effectiveness is the most persuasive. In cases of otherwise unexplained watery, non-bloody diarrhea, MC should be considered and colonic biopsied specimens should be taken of normal-appearing mucosa.

PMID: 23419063



This review article on microscopic colitis was written in response to a request from Prof. Shu Dong Xiao, editor of the Journal of Digestive Diseases, the journal of the Chinese Society of Gastroenterology.  The topic was chosen because of its possible relevance to unexplained diarrhea in Asian nations, including China.

Microscopic colitis was once thought to be a rare disorder, but it is now known to be a common cause of diarrhea, perhaps accounting for as much as 10-20% of all cases of chronic non-bloody diarrhea.   The disease probably is present worldwide, but it has been reported most often in North America and Europe; a few reports of the disease in India, China, and African nations  have been published. The reported incidence of microscopic colitis has risen sharply over time, for uncertain reasons. The cause of microscopic colitis remains obscure, and no single mechanism has been defined. An infectious cause has not been implicated.

The diagnosis of microscopic colitis depends on histologic examination of the colonic tissue because the gross appearance of the mucosa most often is normal. Thus, it is important that endoscopists liberally biopsy the colon in patients which unexplained diarrhea even when there does not appear to an indication. Biopsy samples should be taken throughout the colon; sampling the distal colon and rectum only may not be adequate for making the diagnosis.

The histologic characteristics of the two predominant forms of microscopic colitis are these: Lymphocytic colitis has increased numbers of intraepithelial lymphocytes (>20 lymphocytes per 100 epithelial cells), with little or no disruption of the mucosal architecture. Collagenous colitis has an irregularly thickened subepithelial collagen band, with entrapped microvasculature and inflammatory infiltrate. The band, which normally is 2-3 µm thick, is about 10-20 µm or more in collagenous colitis.

Since few treatments for microscopic colitis have been adequately studied, no absolute recommendations concerning their effectiveness can be made.  It is not clear whether many medications (bismuth subsalicylate, prednisolone, probiotics, mesalamine and cholestyramine) that have been tried are effective in either lymphocytic colitis or collagenous colitis. The most persuasive data indicate that budesonide is effective and well tolerated for inducing and maintaining clinical and histological responses in patients with collagenous colitis, and for inducing clinical and histological responses in patients with lymphocytic colitis.


William R. Brown, M.D.,

Emeritus Professor of Medicine,

University of Colorado School of Medicine,

Denver CO, USA

William Brown



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