Crohn's disease
Exam Tips
- Use the triad 'skip lesions + transmural inflammation + perianal disease' to distinguish Crohn's disease from ulcerative colitis in OSCE/viva answers.
- In stations with diarrhoea and weight loss, always ask about nocturnal stools, perianal symptoms, smoking history, and extra-intestinal features (joints, eyes, skin, liver).
- For investigation sequencing, state: exclude infection, measure faecal calprotectin, then confirm with ileocolonoscopy/biopsy and cross-sectional imaging (MR enterography).
- Name one emergency complication and action: suspected abscess/perforation/obstruction requires urgent imaging, sepsis management, and early surgical input.
- Safety scoring point: long-term steroids are inappropriate for maintenance; mention steroid-sparing therapy and pre-biologic infection screening.
- Image-based exam cue: recognise cobblestoning, deep linear ulcers, creeping fat, and fistula tracks (see figure from your IBD endoscopy/radiology revision chapter).
Definition
Crohn's disease is a chronic, immune-mediated inflammatory bowel disease with a relapsing-remitting course and patchy transmural inflammation that can involve any part of the gastrointestinal tract from mouth to anus. It classically produces discontinuous "skip" lesions (most often terminal ileum and/or colon), and unlike ulcerative colitis it affects the full bowel wall, predisposing to strictures, fistulae, and perianal disease.
Pathophysiology
In genetically susceptible individuals, environmental triggers (especially smoking and prior infectious gastroenteritis) drive dysregulated mucosal immunity against gut microbiota, with excess pro-inflammatory cytokine signalling (including TNF, IL-12/23 pathways). Ongoing transmural inflammation causes deep ulceration, oedema, fibrosis, and mesenteric fat wrapping, leading to fibrostenotic narrowing and penetrating complications (fistula/abscess). Malabsorption, chronic blood/inflammatory loss, and reduced intake contribute to weight loss, iron deficiency, B12/folate deficiency, and growth/puberty delay in younger patients. Histology may show focal chronic active inflammation and non-caseating granulomas (supportive but not universal). For visual pattern recognition in revision, correlate endoscopic cobblestoning and linear ulcers with radiological strictures/fistula tracks (see figure from your core GI pathology chapter on IBD morphology).
Risk Factors
- Family history of Crohn's disease (strong familial aggregation; increased sibling risk)
- Current smoking (higher incidence, relapse risk, and postoperative recurrence risk)
- Previous infectious gastroenteritis (relative risk increased, especially in the following year)
- Recent appendicectomy (short-term increased observed risk; association may be confounded)
- NSAID exposure (may precipitate flare/exacerbation in some patients)
- Current oral contraceptive use (modestly increased risk reported)
Clinical Features
Symptoms
- Persistent diarrhoea >4-6 weeks, often nocturnal
- Abdominal pain (commonly right iliac fossa/colicky if subacute obstruction)
- Fatigue, malaise, anorexia, low-grade fever, weight loss
- Urgency, tenesmus, mucus or blood in stool when colonic involvement is present
- Perianal pain/discharge; recurrent perianal abscess/fistula symptoms
- Symptoms suggestive of fistulation: pneumaturia/faecaluria (enterovesical), passage of stool/flatus per vagina (enterovaginal)
Signs
- Abdominal tenderness or palpable mass (often right lower quadrant)
- Perianal skin tags, fissures, fistula openings, abscess tenderness
- Pallor, aphthous oral ulcers, finger clubbing
- Evidence of malnutrition or dehydration; in children faltering growth/delayed puberty
- Extra-intestinal findings: large-joint oligoarthritis, erythema nodosum, episcleritis/uveitis, hepatobiliary abnormalities
Investigations
Management
Lifestyle Modifications
- Smoking cessation is a core disease-modifying intervention
- Dietetic support: correct calorie/protein deficits, iron/B12/folate/vitamin D deficiencies; consider exclusive enteral nutrition particularly in paediatrics
- Avoid or minimise NSAIDs where possible due to flare risk
- Vaccination review and infection risk counselling before immunosuppression; psychosocial support for school/work impact
Pharmacological Treatment
Corticosteroids for induction of remission (not maintenance)
- Budesonide (modified-release) 9 mg once daily for up to 8 weeks (mild ileocaecal disease)
- Prednisolone oral 40 mg once daily, then taper gradually (commonly by 5 mg/week over ~8 weeks)
- Hydrocortisone IV 100 mg four times daily (or equivalent) in severe hospitalised flare
Use shortest effective course; monitor glucose, blood pressure, mood, infection risk, and bone protection in prolonged/repeated courses. Avoid long-term steroid dependence.
Immunomodulators (steroid-sparing maintenance; specialist use)
- Azathioprine 2-2.5 mg/kg once daily
- Mercaptopurine 0.75-1.5 mg/kg once daily
- Methotrexate 25 mg once weekly SC/IM for induction, then 15 mg once weekly for maintenance + folic acid 5 mg weekly (different day)
Check TPMT activity before thiopurines; monitor FBC/LFT/U&E regularly. Important safety: pancreatitis, hepatotoxicity, myelosuppression. Methotrexate is teratogenic and contraindicated in pregnancy; ensure contraception and alcohol moderation.
Biologic or targeted therapies for moderate-severe/refractory disease (specialist initiated)
- Infliximab 5 mg/kg IV at weeks 0, 2, 6 then every 8 weeks
- Adalimumab 160 mg at week 0, 80 mg at week 2, then 40 mg every other week
- Ustekinumab IV weight-based induction then 90 mg SC every 8-12 weeks
- Vedolizumab 300 mg IV at weeks 0, 2, 6 then every 8 weeks
Screen for TB, hepatitis B/C, HIV and sepsis risk before treatment; avoid starting during serious active infection. Counsel on infusion/injection reactions and opportunistic infection risk; follow local biologics pathway.
Antibiotics (adjunctive, especially perianal sepsis/fistulising disease)
- Metronidazole 400 mg orally three times daily
- Ciprofloxacin 500 mg orally twice daily
Use guided by infection/perianal protocol. Metronidazole: avoid alcohol, caution neuropathy with prolonged use. Ciprofloxacin: tendon, QT, CNS adverse effects and interaction cautions.
Symptom and deficiency management
- Iron replacement (e. g, ferrous sulfate 200 mg tablets; IV iron if intolerance/severe deficiency)
- Vitamin B12 replacement (hydroxocobalamin 1 mg IM regimen per deficiency protocol)
- Vitamin D/calcium supplementation when indicated
Treat biochemical deficits proactively; avoid antidiarrhoeals if suspected obstruction or severe colitis.
Surgical / Interventional
- Drainage of intra-abdominal or perianal abscess (often urgently, with antibiotics)
- Seton placement and combined medical-surgical management for complex perianal fistulae
- Limited ileocaecal resection or segmental bowel resection for refractory localised disease, strictures, perforation, or uncontrolled bleeding
- Stricturoplasty for selected fibrostenotic small-bowel disease to preserve bowel length
- Surgery is not curative; postoperative recurrence prevention and surveillance are essential
Complications
- Fibrostenotic strictures causing partial or complete bowel obstruction
- Penetrating disease: enteroenteric, enterovesical, enterovaginal, and perianal fistulae
- Perianal abscesses/fissures and chronic suppuration
- Perforation, intra-abdominal abscess, acute severe colitis/dilatation, significant haemorrhage
- Malnutrition, weight loss, iron deficiency anaemia, B12/folate deficiency, osteopenia/osteoporosis
- Growth failure and delayed puberty in children/adolescents
- Increased long-term colorectal cancer risk with colonic involvement (comparable to ulcerative colitis of similar extent)
- Venous thromboembolism and hepatobiliary disease (including primary sclerosing cholangitis)
Prognosis
Crohn's disease is lifelong with fluctuating relapse and remission. Disease location often remains stable, but many patients develop complications over time; around half require surgery within 10 years in cohort data, and postoperative recurrence is common without maintenance strategy. Poorer outcomes are associated with early onset, perianal or penetrating disease, severe initial presentation, steroid requirement at diagnosis, and prior resections.
Sources & References
🏥BMJ Best Practice(3)
💊BNF Drug References(8)
- Adalimumab[management.pharmacological]
- Brodalumab[cautions]
- Brodalumab[contraindications]
- Dexketoprofen[contraindications]
- Infliximab[management.pharmacological]
- Methotrexate[management.pharmacological]
- Naloxegol[cautions]
- Upadacitinib[management.pharmacological]
✅NICE Guidelines(1)
- Crohn's disease[overview]
📖Textbook References(3)
- Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 829)[context]
- Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 829)[context]
- Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 829)[context]