microscopic colitis

Microscopic colitis is a term used to define those clinicopathological entities characterized by chronic watery Diarrhea, normal radiological and endoscopic appearances, and microscopic abnormalities. Specific histopathological appearances can be used to further classify collagenous colitis, lymphocytic colitis and other conditions. Collagenous colitis differs from lymphocytic colitis by the presence of a subepithelial collagen band (=10 µm) adjacent to the basal membrane. Both diseases disclose inflammatory changes in the lamina propria and superficial epithelial damage. Although microscopic colitis is considered a rare condition, increasing awareness of these entities among pathologists and clinicians has resulted in more frequent diagnosis. However, their incidence is not well known.

However, the incidence of lymphocytic colitis is about three times higher than that of collagenous colitis and microscopic colitis should be considered as a major possibility in the work-up of chronic diarrhoea in older women.

Endomicroscopy makes it possible to locate and measure the distribution and thickness of collagenous bands underneath the epithelial layer, thus allowing targeted biopsies. This is a new approach in collagenous colitis, particularly in cases with disrupted subepithelial collagen deposits. At present, randomized biopsies are recommended, preferably from the right colon. The distribution of the collagenous bands can be patchy and segmental in the colon. Confocal endomicroscopy helps differentiate between affected and normal sites and can guide biopsies [Kiesslich et al. 2006, Zambelli et al. 2008].