American Board of Internal Medicine (ABIM) Certification Practice Exam

Which of the following characteristics is typical of lymphocytic colitis?

1. Presence of systemic inflammation

2. Histologic inflammation in normal-appearing colonic mucosa

3. Bleeding diarrhea

4. Thickening of the subepithelial collagen band

The correct answer is: Histologic inflammation in normal-appearing colonic mucosa

Lymphocytic colitis is characterized by histologic inflammation in normal-appearing colonic mucosa. In this condition, the primary histological feature observed during biopsy is an increased number of lymphocytes in the colonic epithelium, despite the macroscopic appearance of the colon being typically normal. This contrasts with other forms of colitis, where visible inflammation or ulceration might be present. The presence of systemic inflammation is not typical with lymphocytic colitis, as this condition often does not provoke systemic symptoms or significant inflammatory responses seen in other types of inflammatory bowel disease. Symptoms tend to be localized to the gastrointestinal tract. Bleeding diarrhea is also not a defining feature of lymphocytic colitis. While patients may experience watery diarrhea, it usually is non-bloody, distinguishing it from conditions that lead to significant gastrointestinal bleeding. Thickening of the subepithelial collagen band is characteristic of collagenous colitis, a related condition but separate from lymphocytic colitis. In lymphocytic colitis, while increased lymphocytes are present, the collagen layer is not typically thickened. Thus, the presence of histologic inflammation in normal-appearing mucosa is a hallmark characteristic of lymphocytic colitis,