Crohn's Disease vs Ulcerative Colitis: Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a group of chronic, relapsing inflammatory conditions of the gut. The two main types are Crohn's disease and ulcerative colitis (UC). They usually start in young adulthood and need long-term specialist care. Their differences are a favourite exam topic.

Crohn's disease versus ulcerative colitis

Site

• Crohn's: anywhere from mouth to anus, most often the terminal ileum.
• UC: rectum and colon only. It starts in the rectum and spreads upwards.

Pattern

• Crohn's: patchy "skip lesions".
• UC: continuous inflammation.

Depth

• Crohn's: transmural (the full thickness of the bowel wall).
• UC: mucosa and submucosa only.

Histology

• Crohn's: non-caseating granulomas.
• UC: crypt abscesses and goblet cell depletion.

Typical symptoms

• Crohn's: abdominal pain, diarrhoea, weight loss, perianal disease.
• UC: bloody diarrhoea, urgency, tenesmus.

Complications

• Crohn's: strictures, fistulae, abscesses, malabsorption.
• UC: toxic megacolon, colorectal cancer risk.

Smoking

• Crohn's: smoking increases the risk and worsens the disease.
• UC: smoking appears protective. This is not a reason to smoke.

Extra-intestinal features

• Joint disease: arthritis, sacroiliitis and ankylosing spondylitis.
• Eye disease: episcleritis and uveitis.
• Skin disease: erythema nodosum and pyoderma gangrenosum.
• Mouth ulcers.
• Primary sclerosing cholangitis, especially with UC.
• Gallstones and kidney stones in Crohn's disease.
• Venous thromboembolism.

Investigations

• Blood tests:
  • full blood count (anaemia, raised platelets)
  • CRP
  • albumin
  • iron studies, B12 and folate
• Stool tests: faecal calprotectin separates inflammation from irritable bowel syndrome; stool cultures and C. difficile testing exclude infection.
• Colonoscopy with biopsies: the key diagnostic test.
• Imaging: MR enterography or small bowel imaging for Crohn's disease.
• In South Asia: intestinal tuberculosis can mimic Crohn's disease and must be excluded.

Treatment principles

• UC, mild to moderate: aminosalicylates (mesalazine) are first-line, given orally and/or rectally.
• Flares of either disease: corticosteroids induce remission, but are not used for maintenance.
• Maintenance:
  • immunomodulators (azathioprine, methotrexate)
  • biologics (anti-TNF drugs such as infliximab and adalimumab, vedolizumab, ustekinumab)
  • small molecules (JAK inhibitors)
  Screen for tuberculosis and hepatitis B before starting biologics.
• Crohn's disease: stopping smoking is essential.
• Surgery:
  • Crohn's: for strictures, fistulae and abscesses. Surgery is not curative, so bowel is preserved where possible.
  • UC: colectomy for severe disease that does not respond to treatment, or for dysplasia or cancer. Surgery is curative for UC.

Acute severe ulcerative colitis

Defined by the Truelove and Witts criteria:

• 6 or more bloody stools a day, plus
• signs of systemic toxicity:
  • fever
  • tachycardia
  • anaemia
  • raised ESR or CRP

It needs admission and:

• IV corticosteroids
• thromboprophylaxis
• an abdominal X-ray to look for toxic megacolon
• daily review with surgeons
• rescue therapy (infliximab or ciclosporin) or colectomy if there is no response

Exam pearls

• Skip lesions, fistulae and granulomas point to Crohn's disease.
• Continuous disease starting at the rectum, with bloody diarrhoea, points to UC.
• Long-standing colitis needs surveillance colonoscopy for colorectal cancer.

For more, see the gastroenterology chapter of our Medicine Companion and the colorectal section of the Surgery Companion.

Test yourself

5 exam-style single-best-answer questions. Choose your answer, then tap “Show answer”.

1. Which feature favours Crohn's disease over ulcerative colitis?

   1. Continuous inflammation from the rectum
   2. Crypt abscesses
   3. Bloody diarrhoea
   4. Toxic megacolon
   5. Non-caseating granulomas and skip lesions
   Show answer

   Answer: E. Non-caseating granulomas and skip lesions
   Granulomas, skip lesions and transmural inflammation are features of Crohn's disease.

2. Which liver disease is strongly associated with ulcerative colitis?

   1. Hepatitis A
   2. Wilson's disease
   3. Haemochromatosis
   4. Primary biliary cholangitis
   5. Primary sclerosing cholangitis
   Show answer

   Answer: E. Primary sclerosing cholangitis
   PSC is particularly associated with UC.

3. Which test helps separate IBD from IBS?

   1. Faecal calprotectin
   2. Lipid profile
   3. TSH
   4. Urine culture
   5. Serum amylase
   Show answer

   Answer: A. Faecal calprotectin
   Calprotectin is raised by intestinal inflammation and is normal in IBS.

4. Before starting anti-TNF therapy, patients should be screened for:

   1. Diabetes
   2. Kidney stones
   3. Gallstones
   4. Thyroid disease
   5. Tuberculosis and hepatitis B
   Show answer

   Answer: E. Tuberculosis and hepatitis B
   Biologics can reactivate latent TB and hepatitis B.

5. Which condition can mimic Crohn's disease in South Asia?

   1. Appendicitis
   2. GORD
   3. Gallstones
   4. Coeliac disease
   5. Intestinal tuberculosis
   Show answer

   Answer: E. Intestinal tuberculosis
   Ileocaecal TB closely resembles Crohn's disease and must be excluded before immunosuppression.

More articles in Gastroenterology & Hepatology

• Peptic Ulcer Disease and H. pylori: Testing and TreatmentCauses of peptic ulcers, alarm features, H. pylori breath and stool tests, eradication regimens, PPI healing and ulcer complications.
• GORD (Acid Reflux): Symptoms, When to Scope and TreatmentGastro-oesophageal reflux disease: risk factors, alarm symptoms for endoscopy, lifestyle advice, PPIs, surgery and Barrett's oesophagus.
• Hepatitis B: Transmission, Serology and TreatmentHepatitis B explained: how it spreads, interpreting HBsAg, anti-HBs and anti-HBc, chronic infection, tenofovir/entecavir and birth-dose vaccination.
• Hepatitis C: Testing and Cure with Direct-Acting AntiviralsHepatitis C in Pakistan and beyond: transmission, anti-HCV and HCV RNA testing, sofosbuvir-based cure, follow-up and prevention.

Browse all 56 articles →

Disclaimer

For education and exam preparation only. This is not medical advice and must not be used to diagnose or treat patients. Always follow current clinical guidelines and the advice of qualified senior colleagues.