[Microscopic colitis]

A 38-year old woman is admitted in the gastroenterology unit for a disabling episode of watery diarrhoea, not bloody and refractory to anti-diarrheic drugs. Different diagnostic exams remain negatives, with the exception of colic biopsies who disclose a lymphocytic colitis, one of the forms of the microscopic colitis entity. Microscopic colitis is an anatomo-clinic syndrome characterized by the presence of histological abnormalities on colic biopsies amongst patients suffering from chronic watery diarrhoea without endoscopic anomalies. Two clinical entities are today well known: collagenous colitis is characterized by a thickening of the sub-epithelial collagen band of the colon; lymphocytic colitis is defined as an increased level of lymphocytic cells, more than 20%, in the epithelial surface of colorectal mucosa. Inflammatory lesions of the chorion and alterations of the epithelial surface are seen in the two types of colitis. Their etiology remains unknown. It could be due to inflammatory lesions from autoimmune origin, activated by various exogenous agents such as bacteria and drugs. Clinical (feminine prevalence, frequent association with auto-immune diseases) and morphological similarities lead to argue and to hypothesis that both entities could represent different stages of the same disease, the lymphocytic colitis being the early stage. Various treatments have been proposed, for instance 5-aminosalicylates, but today mainly synthetic corticoids are used, especially budesonide. Others entities are recently been described: the chronic pericrypt eosinophilic enterocolitis and the colonic epithelial lymphocytosis ("epidemic").