Advances in knowledge on microscopic colitis: From bench to bedside

Microscopic colitis (MC) is a general term that describes a family of chronic inflammatory bowel diseases, including lymphocytic colitis (LC) and collagenous colitis (CC). The two forms are characterized by chronic watery diarrhea with normal or near normal endoscopic colonic appearance and specific histopathological abnormalities.Data from recent epidemiological studies reported the diagnosis of MC from several different regions in the world, providing that it can be a worldwide condition. The etiopathogenesis of MC still remains unknown but it is generally accepted that MC is a multifactorial disease, probably secondary to an abnormal immune reaction in predisposed individuals, triggered by different luminal factors (infections, drugs, autoimmunity and/or bile acids). Furthermore, some studies show that the epithelial barrier function in the colonic mucosa of MC patients is also impaired. Several mucosal factors of intestinal inflammation have been studied in MC, postulating that an aberrant T-lymphocyte response may lead to a chronic gut inflammatory condition, with the infiltration of colonic mucosa by different proportion of subset of T-lymphocytes. Little is known about the specific inflammatory mediators in MC pathogenesis, but a predominant Th1 type cytokine profile has been demonstrated. Currently, a number of medical treatments have been studied in MC patients, following mainly an empirical treatment approach. Further studies are needed in order to obtain prospective and more evidence-based data. In the future, it will be possible to develop causal treatment approaches after better understanding the molecular mechanisms behind the origin of the disease.