Summary

Crohn's disease is a chronic, relapsing inflammatory bowel disease (IBD) that can affect any part of the gastrointestinal tract from mouth to anus, though it most commonly involves the terminal ileum and colon. Unlike ulcerative colitis, Crohn's causes transmural (full-thickness) inflammation, leading to characteristic complications including strictures, fistulae, and abscesses. Inflammation is typically discontinuous ("skip lesions"). The aetiology involves genetic susceptibility, environmental triggers, and immune dysregulation. Treatment aims to induce and maintain remission, prevent complications, and improve quality of life. First-line therapies include corticosteroids for induction and immunomodulators (thiopurines, methotrexate) or biologics (anti-TNF, anti-integrin, anti-IL-12/23) for maintenance.

Key Facts

• Definition: Chronic transmural IBD affecting any part of GI tract
• Age of Onset: Bimodal — 15-30 years and 50-70 years
• Location: Terminal ileum (most common), colon, ileocolonic, upper GI
• Pattern: Skip lesions, transmural inflammation, cobblestoning
• Histology: Non-caseating granulomas (pathognomonic but not always present)
• Complications: Strictures, fistulae, abscesses
• Surgery: Not curative; high recurrence rate

Clinical Pearls

"Crohn's — Mouth to Anus, Skip Lesions, Transmural": Remember the key distinguishing features from UC.

"If Perianal Disease, Think Crohn's": Perianal fistulae and abscesses are common in Crohn's, not UC.

"Anti-TNF Changes the Game": Biologics have transformed Crohn's management, achieving mucosal healing and reducing surgery.

Why This Matters Clinically

Crohn's disease is a lifelong condition causing significant morbidity. Early aggressive treatment can prevent complications and improve long-term outcomes. A multidisciplinary approach involving gastroenterology, surgery, dietetics, and psychology is essential.

Structured Approach

General:

• Nutritional status (weight, BMI)
• Pallor, clubbing, lymphadenopathy

Abdominal:

• Tenderness (RIF/RLQ common)
• Mass (phlegmon, abscess)
• Scars (previous surgery)
• Stomas

Perianal:

• Fistulae, skin tags
• Abscesses
• Fissures

Extra-Intestinal:

• Joints (peripheral arthritis, spine)
• Skin (erythema nodosum, pyoderma)
• Eyes (red eye → uveitis/episcleritis)

Natural History

Crohn's disease is a chronic relapsing-remitting condition. Without treatment, most patients experience flares. Up to 80% require surgery within 20 years of diagnosis. Modern biologic therapy has reduced surgical rates.

Outcomes

Poor Prognostic Factors

• Perianal disease
• Stricturing or penetrating behaviour
• Young age at onset
• Smoking
• Need for steroids at diagnosis
• Extensive disease

Key Guidelines

1. ECCO Guidelines on Crohn's Disease (2023) — European consensus.

2. NICE NG129: Crohn's Disease (2019) — UK pathway.

Landmark Trials

SONIC Trial (2010) — Combination therapy

• Infliximab + Azathioprine vs monotherapy
• Key finding: Combination superior for remission
• Clinical Impact: Supports combination therapy in anti-TNF-naive patients

UNITI Trials (2016) — Ustekinumab

• Key finding: Ustekinumab effective for anti-TNF failures
• Clinical Impact: IL-12/23 inhibition as alternative mechanism

Evidence Strength

What is Crohn's Disease?

Crohn's disease is a type of inflammatory bowel disease (IBD). It causes inflammation in your digestive tract, usually the small intestine and/or colon. The inflammation can cause pain, diarrhoea, weight loss, and tiredness.

What causes it?

The exact cause isn't known, but it involves your immune system attacking your gut. Genetics, environment, and gut bacteria all play a role. Smoking makes it worse.

What are the symptoms?

• Diarrhoea (sometimes with blood)
• Abdominal pain, often on the right side
• Weight loss
• Tiredness
• Mouth ulcers
• Problems around the bottom (fistulas, abscesses)

How is it treated?

1. Steroids: To calm flare-ups quickly (short-term only)
2. Immune-modifying drugs: Azathioprine, methotrexate for long-term control
3. Biological medicines: Injections or infusions that target specific parts of the immune system
4. Surgery: Sometimes needed for complications like blockages or abscesses

What to expect

• Crohn's is a lifelong condition with flares and remissions
• Most people can live normal lives with treatment
• Regular check-ups and monitoring are important
• You may need to adjust treatment over time

When to seek help

See your doctor or IBD team if:

• Your symptoms get worse
• You have severe abdominal pain or bloating
• You can't keep food or fluids down
• You have a high fever
• You notice new symptoms