The histopathology of lymphocytic colitis (LC) is similar to that of collagenous colitis (CC), except that the subepithelial collagen band is not present in LC. Crypt architecture is intact. There is increased number of lymphocytes and plasma cells in the lamina propria.
The plasmacytosis in the lamina propria tends to be superficial (located toward the lumenal side). As with collagenous colitis, there is also increased intraepithelial lymphocytes. You must be careful not to look at colonic epithelium overlying a lymphoid follicle when evaluating for intraepithelial lymphocytes. There will often be increased epithelial lymphocytes and this is a normal finding. In the center of this image, there is a cluster of lymphocytes and plasma cells; it is not a lymphoid aggregate (in case you were wondering).
Another image demonstrating numerous intraepithelial lymphocytes in the crypts as well as on the surface epithelium. The lamina propria is also filled with lymphocytes, plasma cells and a few eosinophils.
A different case shows a detectable increase in superficial intraepithelial lymphocytes. However, the degree of surface injury is not signficiant and overall the lamina propria does not appear altered by superficial plasmacytosis. This is actually an example of resolving infectious colitis, which can mimic lymphocytic colitis.
Again, compare the surface injury to this case of lymphocytic colitis, which shows significant changes including mucin depletion.
Microscopic colitis comes in two flavors: collagenous colitis (CC) and lymphocytic colitis (LC). As in CC, the pathogenesis of LC may be due to an antigen in the bowel lumen inciting an autoimmune response. For example, the drug ranitidine has been shown to cause LC. LC has an even stronger association with celiac disease than CC.1
Similar to CC, LC patients present with chronic nonbloody diarrhea and normal endoscopic findings. As in CC, LC affects middle-aged persons, but with equal sex predilection (versus in CC, the F:M ratio is 10:1).
Benign: most patients do well with therapy.
1 Iacobuzio-Donahue CA, Montgomery EA. Gastrointestinal and Liver Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elsevier; 2005: pg 338-9, 398-400.
To learn about the other variation of microscopic colitis, please view our collagenous colitis case.