PassFinals
Gastroenterology & Nutrition

Crohn's Disease

Patchy inflammation of any part of the gut from mouth to anus that extends through the full thickness of the bowel wall, producing strictures, fistulae and abscesses.

In a nutshell

Patchy, full-thickness inflammation anywhere from mouth to anus, most often the terminal ileum. Confirm activity objectively, induce remission with a corticosteroid at a real dose, then get the patient off steroids.

Classic presentation

A young adult with months of crampy right iliac fossa pain, non-bloody diarrhoea, weight loss and mouth ulcers, with perianal skin tags or a fistula.

Key points

  • Granulomas appear in a minority and are not needed for diagnosis. Reaching the terminal ileum at colonoscopy is what matters.
  • Aminosalicylates are less effective than corticosteroids or budesonide. NICE reserves them for people who cannot or will not take those treatments.
  • Ileal disease or resection causes vitamin B12 deficiency and bile-acid diarrhoea, which persists once inflammation is controlled.
  • After ileocaecal resection, reassess endoscopically at 6 months. Recurrence at the anastomosis is the rule.
  • Methotrexate is contraindicated in pregnancy. Metoject product information requires contraception during treatment and for at least 6 months after women stop, and for at least 3 months after men stop; arrange an individual pre-conception plan with the IBD team because specialist guidance differs.

First-line investigation

Faecal calprotectin (a stool marker of bowel inflammation) with stool culture and Clostridioides difficile toxin, plus FBC, CRP, U&E, LFT, albumin, ferritin, vitamin B12 and folate.

Management

Stabilise the acute flare

  • Admit for obstruction, perforation, abscess, sepsis, severe dehydration or heavy bleeding. Give crystalloid with potassium; involve the surgeons early.1,2
  • For admitted active IBD, assess VTE and bleeding risk. Give enoxaparin 4000 units (40 mg) subcutaneously daily unless contraindicated, or 2000 units (20 mg) if creatinine clearance is 15 to 30 mL/min.2,5
  • Send stool culture and Clostridioides difficile toxin before escalating immunosuppression. After gastroenterology review, follow the local acute IBD steroid protocol; hydrocortisone 100 mg intravenously four times daily is one licensed-range regimen.2,4

Confirm inflammation is the problem

  • Faecal calprotectin, stool microbiology and bloods, then ileocolonoscopy with terminal ileal biopsies. Small-bowel MRI (MR enterography); pelvic MRI for perianal sepsis.2,1

Induce remission

  • Follow gastroenterology and the local protocol. A common regimen within the prednisolone SmPC range is 40 mg each morning, reduced by 5 mg weekly; current national Crohn guidance gives no exact dose.2,1,6
  • Mild ileocaecal disease: ileal-release budesonide 9 mg each morning for up to 8 weeks, tapered over the last 2 to 4 weeks.7,2
  • Neither prednisolone nor budesonide maintains remission. Never prescribe either as maintenance.1,2

Spare the steroid

  • Two or more flares in 12 months, or a steroid that will not taper: refer for specialist treatment selection. NICE permits azathioprine or mercaptopurine, but BSG 2025 advises against immunomodulator monotherapy for moderate-to-severe disease.1,2,8
  • If specialist review selects methotrexate for an appropriate patient, prescribe it weekly, never daily, and monitor FBC, LFT, albumin and creatinine. It is not the default monotherapy for moderate-to-severe disease.9,2

Refer for specialist and surgical treatment

  • Refer moderate-to-severe, repeatedly steroid-treated, perianal or penetrating disease for advanced therapy. Options include TNF inhibitors, ustekinumab, vedolizumab, risankizumab, upadacitinib, mirikizumab and guselkumab; eligibility and sequence are specialist decisions.1,2,10,11,12,13
  • Drain a perianal abscess and place a seton (a soft drain left through the fistula tract) before immunosuppression. Obstructing strictures need dilatation, strictureplasty or resection.2,1

Prevent relapse and cancer

  • Complete smoking cessation: smoking roughly doubles relapse risk and raises repeat-surgery risk about two and a half fold. Cutting down does not help.2
  • Yearly weight, haemoglobin, ferritin, vitamin B12, folate and vitamin D. Keep vaccinations current; avoid live vaccines on immunosuppression.2,1
  • Crohn's colitis beyond one segment: NICE CG118 gives a baseline dye-spray colonoscopy at 10 years, then 5, 3 or 1 yearly by risk.14
  • The 2025 British Society of Gastroenterology (BSG) guideline moves that baseline to 8 years, or to diagnosis with primary sclerosing cholangitis.15

Exam traps

  • Admitted active inflammatory bowel disease usually needs enoxaparin 4000 units (40 mg) subcutaneously daily after VTE and bleeding assessment. Bloody diarrhoea alone is not a contraindication; active disease is prothrombotic.
  • A perianal abscess is drained first. Escalating immunosuppression over undrained pus is the classic wrong answer.
  • A fibrotic stricture causing obstruction will not respond to steroids or biologics. It needs dilatation or surgery.
  • Methotrexate is weekly, never daily. Daily prescribing is a recognised cause of fatal marrow suppression.
  • Smoking worsens Crohn's disease but is linked to a milder course in ulcerative colitis. Advise cessation in both.
  • Exclude Clostridioides difficile and enteric infection before calling a flare inflammatory; both mimic and trigger relapse.

Illustrations

Resected terminal ileum and colon in Crohn's diseaseOpened resection specimen of terminal ileum, caecum and ascending colon showing thickened, cobblestoned mucosa, with diseased segments separated by normal bowel (skip lesions).Denis Desaulniers and Bernard Tetu, Wikimedia Commons · CC-BY-SA-4.0
Erythema nodosum in Crohn's diseaseTender erythematous shin nodules, an extraintestinal manifestation that usually tracks with bowel disease activity.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0

Key sources

  1. NICE NG129, Crohn's disease: management (recommendations)Published 3 May 2019
  2. British Society of Gastroenterology, guidelines on inflammatory bowel disease in adults: 2025Published 23 Jun 2025 | Updated 25 Sept 2025
  3. NHS, Crohn's diseaseUpdated 19 Sept 2024
  4. Summary of product characteristics, Hydrocortisone 100 mg powder for solution for injection or infusion (Licensed for regional ileitis (Crohn's disease); adult dose 100 to 500 mg intravenously, repeated at 2, 4 or 6 hours as indicated by response. This does not establish a Crohn-specific national regimen)Updated 2 Sept 2025
  5. Summary of product characteristics, Inhixa 4,000 units (40 mg)/0.4 mL enoxaparin sodium solution for injection
  6. Summary of product characteristics, Prednisolone 5 mg tablets (Licensed for regional ileitis (Crohn's disease); general adult initial dose 5 to 60 mg daily. It does not specify the common Crohn regimen of 40 mg daily reduced by 5 mg weekly)Updated 25 Apr 2023
  7. Summary of product characteristics, Entocort CR 3 mg capsules (ileal-release budesonide)Updated 1 Jul 2023
  8. Summary of product characteristics, azathioprine 50 mg film-coated tabletsUpdated 11 Nov 2025
  9. Summary of product characteristics, Metoject PEN 25 mg solution for injection (methotrexate)Updated 18 Sept 2024
  10. NICE TA888, Risankizumab for previously treated moderately to severely active Crohn's diseasePublished 17 May 2023
  11. NICE TA905, Upadacitinib for previously treated moderately to severely active Crohn's diseasePublished 12 Jul 2023
  12. NICE TA1080, Mirikizumab for previously treated moderately to severely active Crohn's diseasePublished 10 Jul 2025
  13. NICE TA1095, Guselkumab for previously treated moderately to severely active Crohn's diseasePublished 28 Aug 2025
  14. NICE CG118, colorectal cancer prevention: colonoscopic surveillance in adults with ulcerative colitis, Crohn's disease or adenomasPublished 23 Mar 2011 | Updated 20 Sept 2022
  15. British Society of Gastroenterology, guidelines on colorectal surveillance in inflammatory bowel diseaseUpdated 12 Mar 2025

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.