Crohn's Disease

🔍 When to Suspect

Persistent diarrhoea (may be bloody), abdominal pain, and unexplained weight loss, often with systemic features (fatigue, fever) or perianal issues

From the full topic in The Ocean Library: Crohn's Disease

🧭 When to suspect

Crohn's disease is a chronic, relapsing–remitting transmural inflammation that can affect any part of the gut from mouth to anus, classically in discontinuous “skip lesions”, with the terminal ileum and ileocaecal region most commonly involved. Onset is usually before the age of 30 but it can present at any age.

Suspect Crohn's in a patient with persistent diarrhoea (typically > 4–6 weeks, which may be bloody or nocturnal), cramping abdominal pain (often right iliac fossa) and unexplained weight loss. Raise suspicion further when these are joined by systemic features (fatigue, fever, malaise) or by extra-intestinal manifestations – perianal disease, aphthous mouth ulcers, joint, eye or skin problems. Symptoms characteristically fluctuate between flares and remission. The primary-care skill is to recognise the pattern, use faecal calprotectin to separate inflammatory bowel disease from IBS, exclude mimics, and refer for colonoscopy and biopsy – the definitive diagnostic step.

Feature	Crohn's disease	Ulcerative colitis
Distribution	Any site, mouth to anus; skip lesions (terminal ileum/ileocaecal common)	Colon only; continuous from the rectum
Depth	Transmural (full thickness)	Mucosal / submucosal
Characteristic features	Perianal disease, fistulae, strictures, abscesses	Bloody diarrhoea, urgency, tenesmus
Smoking	Worsens disease and post-operative recurrence	Associated with reduced risk (“protective”)
Histology	Non-caseating granulomas (not always seen)	Crypt abscesses, goblet-cell depletion

Source: British Society of Gastroenterology · NICE NG129

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