Which description best characterizes colonoscopy findings in ulcerative colitis?

• A. Transmural thickening with fistulas.
• B. Segmental Crohn's like involvement with cobblestone mucosa.
• C. Continuous mucosal inflammation starting at the rectum and extending proximally, with erythema and friability.
• D. Patchy transmural inflammation with skip lesions.

Answer: (C)

The main pattern being tested is how ulcerative colitis appears on colonoscopy. Ulcerative colitis characteristically shows continuous mucosal inflammation that begins in the rectum and extends proximally without any intervening normal segments. The inflammation is superficial, confined to the mucosa and submucosa, and the mucosa becomes erythematous, friable, and easily bleeds; there may also be mucosal edema and, over time, pseudopolyps. This continuous, rectum-to-colon involvement with only mucosal-level damage is what sets UC apart from Crohn’s disease.

The other descriptions describe Crohn’s disease features, not ulcerative colitis: transmural involvement with fistulas reflects full-thickness bowel wall disease; segmental or patchy involvement with cobblestoning and skip lesions is typical of Crohn’s; and patchy transmural inflammation with skip areas again points to Crohn’s.