## Ulcerative Colitis: Pathology and Complications ### Depth and Distribution of Inflammation **Key Point:** Ulcerative colitis is a **mucosal and submucosal disease** — inflammation is limited to the inner layers and does NOT extend transmurally. This fundamental distinction from Crohn's disease determines the pattern of complications. ### Complications of Ulcerative Colitis | Complication | UC | Crohn's Disease | Mechanism | |--------------|----|-----------------|-----------| | **Toxic megacolon** | Yes (acute) | Yes (acute) | Loss of muscle tone from severe inflammation | | **Fistulas** | Rare/absent | Common | Requires transmural disease | | **Strictures** | Rare (fibrotic only) | Common | Transmural fibrosis | | **Colorectal cancer** | Yes (increased risk) | Yes (increased risk) | Chronic mucosal inflammation and dysplasia | | **Perforation** | Possible (toxic megacolon) | Yes (fistulous tracts) | Different mechanisms | ### High-Yield: **Fistula formation and strictures are complications of CROHN'S DISEASE, NOT ulcerative colitis.** These require transmural inflammation, which UC lacks by definition. In UC, strictures are rare and occur only late from fibrosis of healed ulcers. ### Clinical Pearl: The three correct statements about this patient's UC are: 1. **Mucosal/submucosal inflammation only** — explains why perforation is less common than in Crohn's 2. **Toxic megacolon risk** — acute, life-threatening complication requiring emergency colectomy if medical management fails 3. **Colorectal cancer surveillance** — dysplasia-associated lesion or mass (DALM) develops in 5–10% after 20 years; colonoscopy every 1–2 years recommended after 8–10 years of disease ### Mnemonic: **UC = Mucosal disease → No fistulas** **Crohn's = Transmural disease → Fistulas & strictures** [cite:Harrison 21e Ch 297]
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