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 exi sts. Some forms of minimal-change colitis may overlap with ''self-limi ted'' colitis (infectious colitis) or may be due to (surreptitious) us e of laxatives or other drugs. In recent years it has become clear how ever that some genuine forms of chronic colitis can be diagnosed only by microscopic examination of multiple colonic biopsies while macrosco py is negative and hence can be called ''microscopic colitis''. Collag enous colitis and lymphocytic colitis are at present two forms of this type of colitis which are more or less well defined both clinically a nd pathologically. Chronic watery diarrhoea is the main symptom for bo th. The symptoms of collagenous colitis appear most commonly in the si xth decade. Women are affected about 4 times more frequently than men. The major microscopic characteristic is a thickened collagen layer un derneath the intercryptal surface epithelium. The major characteristic of lymphocytic colitis is an increase in number of interepithelial ly mphocytes. Both conditions arc characterized by signs of mucosal infla mmation. Clinically, collagenous colitis is characterized by long-last ing diarrhoea. In patients with lymphocytic colitis the period of chro nic diarrhoea is usually shorter and female predominance is less appar ent. Although the natural history of these forms of colitis is not pre cisely known, it appears from the data thus far published that the lon g-term consequences are unlikely to be dire. The true incidence, aetio logy and pathogenesis are unknown for both conditions and treatment is unclear. Several studies of patients investigated for idiopathic chro nic diarrhoea have shown that collagenous colitis and lymphocytic coli tis are common disorders within these groups of patients (up to 27%). It is important, therefore, to recognize the disease in order to reass ure the patients and to avoid more expensive examinations. The diagnos is can be made easily by obtaining multiple biopsies during colonoscop y. One single rectal biopsy is indeed not enough as both lymphocytic a nd collagenous colitis present as pancolitis and the microscopic diagn ostic features may be variably expressed in different parts of the col on.