Crohn’s Disease

Crohn’s disease is a type of inflammatory bowel disease (IBD) characterised by chronic, relapsing inflammation of the gastrointestinal (GI) tract. It can affect any part of the GI tract from the mouth to the anus, most commonly the terminal ileum. Unlike ulcerative colitis, the inflammation in Crohn’s disease is transmural (involving all layers of the bowel wall) and often discontinuous (“skip lesions”).

Peak Incidence

• Bimodal distribution:
  • Primary peak: 15–30 years
  • Secondary peak: 60–80 years
• Slightly more common in females and in individuals of Ashkenazi Jewish descent.

Pathophysiology

• The exact cause is unknown, but genetic susceptibility (e.g. NOD2 mutations), dysregulated immune response, gut microbiota, and environmental factors contribute.
• Chronic inflammation causes transmural damage, leading to ulcers, strictures, fistulas, and granuloma formation on histology.
• Disease is segmental, with skip lesions and intervening normal mucosa.

Symptoms

• Chronic diarrhoea (often non-bloody)
• Right lower quadrant abdominal pain
• Weight loss and malnutrition
• Fatigue
• Fever (in active or severe flares)
• Perianal symptoms (e.g. pain, discharge, fistulas)

Signs

• Abdominal tenderness, especially in the right iliac fossa
• Palpable mass (thickened bowel or abscess)
• Perianal disease: fissures, skin tags, abscesses, fistulas
• Oral aphthous ulcers
• Clubbing (chronic inflammation)

Extra-intestinal manifestations

• Skin: Erythema nodosum, pyoderma gangrenosum
• Joints: Arthritis (axial, peripheral)
• Eyes: Uveitis, episcleritis
• Hepatobiliary: Gallstones, primary sclerosing cholangitis (less common in Crohn’s than UC)

Diagnosis

First-Line Test

• Faecal calprotectin – highly sensitive marker of intestinal inflammation (~90%).

Gold Standard

• Colonoscopy with biopsy (if patient is stable):
  • Skip lesions
  • Cobblestone appearance
  • Transmural inflammation
  • Non-caseating granulomas
  • Increased goblet cells

Further Investigations

• Blood tests:
  • FBC – anaemia
  • CRP/ESR – inflammation
  • Vitamin B12 and vitamin D – deficiency due to malabsorption
  • Anti-tTG antibodies – to rule out coeliac disease
  • U&Es, LFTs
• Stool tests:
  • Stool culture and microscopy – exclude infective causes
• Imaging:
  • MRI enterography – preferred for assessing fistulas and strictures
  • CT abdomen/pelvis – for acute complications (e.g. abscess)
  • Barium studies – less commonly used; may show strictures, “string sign”

Complications

• Strictures – can cause bowel obstruction
• Fistulas – entero-enteric, enterocutaneous, recto-vaginal (most common fistula site)
• Perianal disease – abscesses, fissures, fistulas
• Osteoporosis – due to inflammation, corticosteroids, and malabsorption
• Colorectal cancer – increased risk with longstanding disease
• Nutritional deficiencies – iron, B12, folate, fat-soluble vitamins
• Growth delay – in children
• Psychosocial impact – depression, anxiety, reduced quality of life

Management

Acute Flare

• Glucocorticoids (first-line):
  • Oral prednisolone or IV hydrocortisone
  • Budesonide for mild ileocaecal disease
• 5-ASA (e.g. mesalazine) – less effective in Crohn’s than UC, may have limited role in mild colonic disease
• Immunomodulators:
  • Azathioprine, mercaptopurine – not for induction alone but added to maintain remission
  • Methotrexate – alternative for thiopurine-intolerant patients
• Biologics:
  • Anti-TNF agents (infliximab, adalimumab) for refractory disease or steroid-dependent patients
  • Consider in perianal Crohn’s or frequent exacerbations
• Antibiotics:
  • Metronidazole for isolated perianal disease or abscesses
• Enteral nutrition:
  • First-line for induction in paediatric patients
  • May be used in adults to avoid corticosteroids

Maintenance of Remission

• Lifestyle:
  • Smoking cessation – strongly advised (worsens Crohn’s disease)
• First-line:
  • Azathioprine or mercaptopurine
• Second-line:
  • Methotrexate
• Refractory cases:
  • Biologic therapy

Surgical Management

• Up to 80% of patients require surgery over their lifetime
• Not curative – recurrence is common at the anastomotic site

Indications for surgery

• Strictures causing obstruction
• Fistulas or abscesses not responding to medical therapy
• Perforation or toxic megacolon
• Severe perianal disease
• Failure of medical therapy

Surgical options

• Segmental small bowel resection
• Stricturoplasty – preserves bowel length
• Proctectomy – in severe perianal Crohn’s
• Ileoanal pouch – not recommended (high risk of failure)

Perianal Disease

• Oral metronidazole for symptomatic relief
• Anti-TNF therapy (e.g. infliximab) for fistula healing
• Draining seton placement for complex fistulas – prevents abscess formation and premature closure
• Perianal abscess:
  • Requires incision and drainage
  • Consider prophylactic antibiotics in high-risk cases