American Board of Internal Medicine (ABIM) Certification Practice Exam

What histologic finding is classic for diagnosing lymphocytic colitis?

1. Increased subepithelial collagen bands

2. Intraepithelial lymphocytosis

3. Thickening of mucosal epithelium

4. Crypt distortion

The correct answer is: Intraepithelial lymphocytosis

Intraepithelial lymphocytosis is a classic histologic finding associated with lymphocytic colitis. This condition is characterized by an increased number of lymphocytes within the epithelial layer of the colonic mucosa. Histologically, this can be observed as a significant infiltration of lymphocytes between the epithelial cells, which is a distinct feature that can help differentiate lymphocytic colitis from other types of colitis. Understanding the significance of intraepithelial lymphocytosis is crucial, as it directly correlates with the inflammatory process occurring in lymphocytic colitis, which typically results in chronic diarrhea and abdominal discomfort. The presence of these intraepithelial lymphocytes is often a key indicator that can lead to a diagnosis, especially when combined with clinical history and other findings. While increased subepithelial collagen bands, thickening of the mucosal epithelium, and crypt distortion may be seen in other forms of colitis or gastrointestinal disorders, they are not specific markers for lymphocytic colitis. Subepithelial collagen bands are more associated with collagenous colitis, while crypt distortion is typically seen in inflammatory bowel diseases like Crohn's disease or ulcerative colitis. Therefore, recognizing intraepithelial lymphocyt