American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the classic finding in the histologic evaluation for microscopic colitis?

1. Dense fibrous tissue

2. Intraepithelial lymphocytosis

3. Granulomatous inflammation

4. Crypt abscesses

The correct answer is: Intraepithelial lymphocytosis

The classic finding in the histologic evaluation for microscopic colitis is intraepithelial lymphocytosis. In microscopic colitis, which includes types such as lymphocytic colitis and collagenous colitis, there is a notable increase in the number of lymphocytes present in the epithelial layer of the colon. This lymphocyte infiltration is a key diagnostic feature and can help differentiate microscopic colitis from other forms of colitis. The histological characteristics of microscopic colitis are typically subtle and may not show significant changes in the architecture of the tissue, which is why intraepithelial lymphocytosis is particularly important. In lymphocytic colitis, for instance, the increased lymphocytes are observed in the surface epithelium and the intraepithelial spaces. The other choices, while relevant to different types of inflammatory bowel disease or conditions, do not represent the hallmark finding for microscopic colitis. Dense fibrous tissue, granulomatous inflammation, and crypt abscesses are more characteristic of other conditions, such as Crohn's disease or ulcerative colitis, rather than microscopic colitis specifically.