Microscopic colitis refers to two medical conditions - collagenous colitis and lymphocytic colitis - which cause diarrhoea. They are characterised by a triad of clinicopathological features as follows: 1. Chronic watery diarrhoea; 2. Normal colonoscopy; 3. Characteristic histopathology.

Clinical features

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Patients are characteristically, though not exclusively, middle-aged females. They present with a long history of watery diarrhoea, which may be profuse. There is a higher incidence of autoimmune diseases, for example arthritis, Sjögren's syndrome, and coeliac disease, in patients with microscopic colitis. There are reports of associations with multiple drugs, especially non-steroidal anti-inflammatory drugs.

Colonoscopy is normal or near normal. The changes are often patchy, so multiple colonic biopsies must be taken in order to make the diagnosis. A full colonoscopy is required, as an examination limited to the rectum will miss cases of microscopic colitis

Pathology

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The hallmark of microscopic colitis is an increase in inflammatory cells in colonic biopsies with an otherwise normal appearance and architecture. Inflammatory cells are increased both in the surface epithelium ("intraepithelial lymphocytes") and in the lamina propria. In lymphocytic colitis, these are the only abnormal features.

In collagenous colitis, the features of lymphocytic colitis are present, with in addition the presence of a thickened subepithelial collagen layer which may be up to 30 micrometres thick.

Treatment

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No single treatment is accepted as the standard, and measuring response is difficult. Often a trial of anti-diarrhoeals is followed by anti-inflammatory drugs. Drugs that have been used in the treatment of microscopic colitis include 5-aminosalicylic acid, bismuth, and steroids.

See also

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• Colitis

External Link

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• Microscopic Colitis