American Board of Internal Medicine (ABIM) Certification Practice Exam

In lymphocytic colitis, the histologic hallmark is an increase in intraepithelial lymphocytes. This condition is characterized by a significant infiltration of lymphocytes within the epithelial layer of the colonic mucosa, often accompanied by a relatively normal architecture of the colonic mucosa. The presence of these lymphocytes is essential for diagnosis, as it indicates an immune-mediated process affecting the colonic lining.

While other findings may be noted in varying forms of colitis, lymphocytic colitis is specifically distinguished by this increase in intraepithelial lymphocytes. There might be minimal alterations in the other histological features, which helps to differentiate it from other types of colitis, such as collagenous colitis, where there are different characteristics, including subepithelial fibrosis.

In summary, the diagnosis of lymphocytic colitis relies heavily on identifying the increased numbers of intraepithelial lymphocytes through histologic examination, making it a key indicator for this condition.