Microscopic colitis (MC) is the common denominator for lymphocytic and
collagenous colitis (CC). It is now recognized as a relatively frequent cause of
diarrhea that equals the prevalence of
inflammatory bowel disease. Patients are typically middle-aged women, but disease may occur at every age. Patients with MC report watery, non-bloody
diarrhea in the absence of endoscopic and radiologic abnormalities.
Lymphocytic colitis is characterized by an increased number of intraepithelial lymphocytes, and CC by a thickened subepithelial
collagen band, whereas in both an increased mononuclear infiltration of the lamina propria is found. The pathogenesis of MC is largely unknown, but may relate to autoimmunity, adverse reactions to drugs or (
bacterial) toxins, and abnormal
collagen metabolism in the case of CC.
Budesonide is so far the only
drug that has proven efficacy in randomized controlled trials both for the induction and maintenance of remission. Patients who are nonresponsive, dependent or who experience side effects on
budesonide may benefit from
thiopurine or anti-TNF treatment, but these options are still experimental. The long-term prognosis of MC is good; it does not appear to predispose to
malignancies and can in some cases be self-limiting. Further research and randomized clinical trials are required to expand our understanding of the natural course and the pathogenesis of MC.