Crohn’s disease
1. Big picture
Crohn’s disease is a chronic relapsing inflammatory bowel disease (IBD) that can affect any part of the gastrointestinal tract from mouth to anus, but most commonly affects the terminal ileum and ileocecal region. The inflammation is transmural, discontinuous, and patchy, producing skip lesions, strictures, fistulas, abscesses, and malabsorption.
Classic exam pattern:
Young patient + chronic diarrhea + right lower quadrant pain + weight loss ± fever ± perianal disease.
The most important contrast is with ulcerative colitis:
| Feature | Crohn’s disease | Ulcerative colitis |
|---|---|---|
| Location | Mouth to anus, especially terminal ileum | Colon only |
| Pattern | Skip lesions | Continuous from rectum |
| Depth | Transmural | Mucosa/submucosa |
| Rectum | May be spared | Almost always involved |
| Bleeding | Less prominent | Common bloody diarrhea |
| Fistula/abscess/stricture | Common | Uncommon |
| Granulomas | Non-caseating granulomas may occur | Not typical |
| Surgery | Not curative | Colectomy can cure colitis |
The attached question file emphasizes exactly this: Crohn disease may occur anywhere in the intestinal tract, terminal ileum is most frequent, healthy and diseased segments may alternate, fistulas are common, and bleeding is less frequent than in ulcerative colitis.
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