Crohn Disease
Transmural inflammation, noncaseating granulomas, skip lesions, cobblestone mucosa, string sign on barium, ASCA+.
Ulcerative Colitis
Mucosal/submucosal inflammation, crypt abscesses, continuous from rectum, lead pipe colon, p-ANCA+.
Toxic Megacolon
Colonic dilation > 6 cm with fever, tachycardia, leukocytosis; strict NPO, IV steroids, antibiotics, surgical consult.
Surveillance Colonoscopy
Begin surveillance colonoscopy 8 years after disease onset, repeating every 1-2 years due to high colorectal adenocarcinoma risk.
Comprehensive Comparison: Crohn Disease vs. Ulcerative Colitis
| Characteristic | Crohn Disease | Ulcerative Colitis |
|---|---|---|
| Gastrointestinal Location | Any segment from mouth to anus (terminal ileum most common); rectal sparing common | Colon only; always starts at the rectum and progresses proximally continuously |
| Depth of Inflammation | Transmural (causes fistulas, strictures, deep fissures, bowel obstruction) | Mucosal and submucosal only (causes superficial ulcerations and pseudopolyps) |
| Endoscopic Pattern | Skip lesions with intervening normal mucosa, aphthous ulcers, cobblestone appearance | Continuous circumferential erythema, loss of vascular markings, friable mucosa |
| Histopathology | Noncaseating granulomas (pathognomonic), transmural lymphoid aggregates | Crypt abscesses containing neutrophils, crypt architectural distortion |
| Smoking Effect | Smoking increases risk, recurrence, and surgical requirement | Smoking appears protective; smoking cessation frequently precipitates disease flare |
Extraintestinal Manifestations of IBD
Extraintestinal manifestations occur in 25-40% of patients and may parallel bowel activity or run an independent course:
- Parallels Bowel Activity: Erythema nodosum, peripheral arthritis, episcleritis, aphthous stomatitis (treat by inducing bowel remission).
- Independent of Bowel Activity: Pyoderma gangrenosum (deep, necrotic ulcer with violaceous borders; do not debride), Ankylosing spondylitis (HLA-B27), Primary Sclerosing Cholangitis (strongly associated with UC; causes bead-like strictures on MRCP).
OMM Board Correlate: Intestinal Autonomic Division
The transition point of autonomic innervation occurs at the Cannon-Böhm point (distal 1/3 of the transverse colon):
- Terminal Ileum / Cecum / Ascending Colon: Sympathetics T10-T11 via Superior Mesenteric Ganglion (SMG). Parasympathetics via Vagus Nerve (CN X).
- Descending Colon / Sigmoid / Rectum: Sympathetics T12-L2 via Inferior Mesenteric Ganglion (IMG). Parasympathetics via Pelvic Splanchnic Nerves (S2-S4).
- Chapman Reflexes: Terminal ileum: right 10th-11th intercostal spaces. Colon: along the anterior iliotibial band.
Board Traps & Common Distractors
- Never perform colonoscopy or give barium enema during a severe active flare of acute ulcerative colitis due to high risk of precipitating toxic megacolon and free bowel perforation.
- Never surgically debride pyoderma gangrenosum; it exhibits pathergy, where mechanical trauma leads to catastrophic ulcer enlargement. Treat with systemic corticosteroids or anti-TNF biologics.
- Avoid opioids, antidiarrheals (loperamide), and anticholinergics in acute colitis as they diminish colonic motility and provoke toxic megacolon.