Crohn's versus ulcerative colitis
Depth and distribution decide everything else. Learn those two rows and the other eight fall out of them.
| Crohn's disease | Ulcerative colitis | |
|---|---|---|
| Location | Mouth to anus, terminal ileum most common | Colon only, starting at the rectum |
| Depth | Transmural, all layers | Mucosa and submucosa only |
| Pattern | Skip lesions, cobblestone appearance | Continuous, extending proximally without gaps |
| Stool | Loose, usually non-bloody, sometimes fatty and foul | Bloody diarrhea with mucus and tenesmus |
| Pain | Right lower quadrant, often with a palpable mass | Left lower quadrant cramping, relieved by defecation |
| Classic complication | Strictures, fistulas, abscesses, perianal disease | Toxic megacolon, massive hemorrhage, perforation |
| Surgery | Relieves, does not cure; disease recurs at anastomoses | Total colectomy is curative and produces an ileostomy |
| Extraintestinal | Arthritis, uveitis, erythema nodosum | Primary sclerosing cholangitis, colon cancer surveillance |
| Nutrition | Terminal ileal disease means vitamin B12 malabsorption; fat malabsorption means gallstones and oxalate kidney stones | Iron loss from chronic bleeding; nutrition otherwise better preserved |
| The tested trap | Perianal fistula is Crohn's, not a hemorrhoid | Antidiarrheals and opioids can tip a flare into toxic megacolon |
The trap row in full
Antidiarrheal agents and opioids slow colonic motility. In a severe ulcerative colitis flare that slowing lets the colon dilate. Abdominal distension with fever, tachycardia, and bowel sounds that are diminishing rather than hyperactive is the trigger. The nurse holds the antidiarrheal, keeps the patient nothing by mouth, and escalates. Do not wait for the abdominal film.
Epidemiology, stated as epidemiology: smoking is associated with worse Crohn's disease, while ulcerative colitis appears more often in people who have never smoked or have recently quit. That is an observed association in populations. It is never advice to a patient.
Memory hookCROHN'S CREEPS, UC CLIMBS. Crohn's creeps in patches through the whole wall anywhere from mouth to anus. Ulcerative colitis climbs continuously and shallowly from the rectum up.
Margin notedepth decides the complication.
TakeawayCrohn's goes through the wall and makes tunnels, ulcerative colitis stays shallow and makes bleeding, and only ulcerative colitis gives you toxic megacolon.
Aminosalicylates, corticosteroids, and biologics → BOOK 05 · P7. Every inflammatory marker value → BOOK 07 · P5.