Collagenous and microscopic colitis: clinical importance. 
Minimal-change colitis and microscopic colitis are clinicopathological terms for diarrhoea with normal endoscopic or barium enema findings.  Some controversy about the exact definitions and terminology still exists.  Some forms of minimal-change colitis may overlap with "self-limited" colitis (infectious colitis) or may be due to (surreptitious) use of laxatives or other drugs.  In recent years it has become clear however that some genuine forms of chronic colitis can be diagnosed only by microscopic examination of multiple colonic biopsies while macroscopy is negative and hence can be called "microscopic colitis".  Collagenous colitis and lymphocytic colitis are at present two forms of this type of colitis which are more or less well defined both clinically and pathologically.  Chronic watery diarrhoea is the main symptom for both.  The symptoms of collagenous colitis appear most commonly in the sixth decade.  Women are affected about 4 times more frequently than men.  The major microscopic characteristic is a thickened collagen layer underneath the intercryptal surface epithelium.  The major characteristic of lymphocytic colitis is an increase in number of interepithelial lymphocytes.  Both conditions are characterized by signs of mucosal inflammation.  Clinically, collagenous colitis is characterized by long-lasting diarrhoea.  In patients with lymphocytic colitis the period of chronic diarrhoea is usually shorter and female predominance is less apparent.  Although the natural history of these forms of colitis is not precisely known, it appears from the data thus far published that the long-term consequences are unlikely to be dire.  The true incidence, aetiology and pathogenesis are unknown for both conditions and treatment is unclear.(ABSTRACT TRUNCATED AT 250 WORDS)