Microscopic colitis: an underdiagnosed cause of chronic diarrhoea--the clue is in the biopsies

Microscopic forms of colitis (collagenous colitis and lymphocytic colitis) are uncommon but important causes of chronic diarrhoea that are often overlooked. The clinical features of these disorders are similar, and they are more common in middle-aged females, although the female predominance is greater in collagenous colitis. Although their cause is unclear, both are associated with a variety of autoimmune diseases. Colonoscopy and barium enema are typically normal, so that the diagnosis depends on the demonstration of characteristic changes on histopathological examination of colorectal biopsies. These should be taken in all patients undergoing colonoscopy for the investigation of chronic diarrhoea. There are no large controlled trials of therapy available. Treatment is empirical, generally using the same agents as for inflammatory bowel -disease. Assessment of therapy is also difficult as spontaneous remissions occur often.