Describe how Crohn's disease differs from ulcerative colitis in terms of pathology and areas involved.

• A. Crohn's disease is limited to mucosa and colon; UC can affect anywhere.
• B. Crohn's can affect any part of the GI tract with skip lesions and transmural inflammation; ulcerative colitis is continuous colonic inflammation limited to mucosa/submucosa starting at the rectum.
• C. Both are limited to mucosa; Crohn's is continuous.
• D. Crohn's is caused by gluten; UC is not.

Answer: (B)

The main idea is how inflammation spreads and where it occurs in the gut. Crohn's disease can affect any part of the gastrointestinal tract from mouth to anus, and it often appears in patches with areas of normal tissue between them (skip lesions). The inflammation is transmural, involving the full thickness of the bowel wall, which explains features like fistulas, abscesses, and strictures. Ulcerative colitis, on the other hand, is limited to the colon and rectum and presents as a continuous inflammatory process that starts at the rectum and extends proximally. The inflammation in UC is confined to the mucosa and submucosa, not the full wall, so fistulas are less typical. This combination—Crohn's affecting any part with skip lesions and transmural involvement versus UC causing continuous mucosal-to-submucosal inflammation confined to the colon—best captures the difference described.