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Inflammatory bowel disease: Crohn's disease and ulcerative colitis
Ulcerative colitis (UC) is continuous mucosal inflammation starting in the rectum, and Crohn's disease is "skipping" transmural inflammation anywhere from mouth to anus; this difference explains the complications (fistulas and strictures in Crohn's, megacolon and bleeding in UC) and the treatment.
Why it matters in the exam
IBD questions first test the distinction: bloody diarrhoea with tenesmus and continuous inflammation from the rectum — UC; right lower quadrant pain, weight loss, fistulas and perianal disease with terminal ileum involvement — Crohn's. Smoking worsens Crohn's and "protects" against UC; primary sclerosing cholangitis (PSC) is linked mainly to UC; ileal Crohn's brings B12 deficiency, gallstones and oxalate kidney stones. On biopsy, non-caseating granulomas point to Crohn's.
The second part is acute severe UC: at least 6 bloody motions daily plus signs of systemic illness (heart rate above 90, temperature above 37.8, Hb below 10.5 g/dL or ESR above 30). Treatment is admission, intravenous steroids, exclusion of Clostridioides difficile and CMV, and heparin thromboprophylaxis despite the bleeding. If there is no response after 3 days — infliximab or ciclosporin, or colectomy. In maintenance: 5-ASA works in mild-moderate UC but not in Crohn's; latent tuberculosis and hepatitis B are checked before biological therapy; and colonoscopic cancer surveillance begins 8 years after disease onset (with PSC — at once and every year).
Key points
- UC: continuous from the rectum, mucosal, bloody diarrhoea, PSC.
- Crohn's: skipping, transmural, terminal ileum, fistulas and granulomas.
- Mild UC: 5-ASA; Crohn's: 5-ASA not effective.
- Acute severe UC: intravenous steroids, heparin, and with no response by day 3 — infliximab, ciclosporin or surgery.
- Surveillance colonoscopy 8 years after onset; before a biologic — tuberculosis and hepatitis B.
Summary table
| Feature | Ulcerative colitis | Crohn's disease | Exam note |
|---|---|---|---|
| Distribution | Continuous from the rectum, colon only | "Skipping", mouth to anus, mainly terminal ileum | Perianal disease points to Crohn's |
| Depth | Mucosa only | Transmural, granulomas | Fistulas and strictures in Crohn's |
| Clues | Bloody diarrhoea, tenesmus; PSC; smoking "protects" | Right lower quadrant pain, weight loss; smoking worsens | Ileal Crohn's: B12 deficiency, gallstones and oxalate stones |
| Mild-moderate treatment | Oral and rectal 5-ASA | Budesonide for ileal disease; 5-ASA not effective | Before a biologic: latent tuberculosis and hepatitis B |
| Moderate-severe disease | Biologic (anti-TNF, vedolizumab, ustekinumab) or JAK inhibitor | Biologic, sometimes with an immunomodulator | Thiopurines: check TPMT |
| Acute severe UC | 6 or more bloody stools + systemic signs | — | Intravenous steroids; no response by day 3: infliximab, ciclosporin or surgery |
Free exam questions
איזה מבין הבאים מ הווה גורם סיכון להתפתחות Crohn`s disease ? (the question as examined, in Hebrew)
- א. גלולות למניעת הריון
- ב. כריתת תוספתן
- ג. מוצא לטיני
- ד. הימנעות מעישון
A 25-year-old male presents to your clinic with abdominal pain, weight loss, and diarrhea over the last 8 months. After a taking the patient’s history and performing a physical examination you suspect inflammatory bowel disease (IBD). Which of the following points to ulcerative colitis rather than Crohn’s disease?
- A. History positive for bowel obstruction 2 months ago
- B. Granulomas on intestinal biopsy
- C. Continuous disease from the anus until 30cm from the anus
- D. Fistulas
לאיזו תרופה מהבאות יש את הקונטראינדיקציה הברורה יותר בטיפול בפסוריאזיס בחולי CROHN'S DISEASE ? (the question as examined, in Hebrew)
- א. APREMILAST
- ב. GUSELKUMAB
- ג. USTEKINUMAB
- ד. SECUKINUMAB
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Sources
- ECCO Guidelines on Therapeutics in Ulcerative Colitis, 2022 — Medical treatment and acute severe ulcerative colitis
- ECCO Guidelines on Therapeutics in Crohn's Disease, 2024 — Medical treatment of luminal Crohn's disease
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Inflammatory Bowel Disease
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.