Toxic megacolon

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Toxic megacolon is a life-threatening complication of colonic inflammation, characterised by acute colonic dilatation (>6 cm in diameter) with systemic toxicity.

Aetiology

Common causes include:

  • Inflammatory bowel disease (IBD): ulcerative colitis (most common) or Crohn’s disease.
  • Infectious colitis: clostridioides difficile infection, cytomegalovirus (CMV) colitis.
  • Ischaemic colitis: due to vascular compromise.
  • Medications: narcotics, anticholinergics, loperamide (reduce colonic motility).
  • Radiation colitis: following pelvic radiotherapy.

Pathophysiology

  • Severe inflammation disrupts neuromuscular function, causing loss of colonic tone and excessive dilatation.
  • Colonic distension leads to ischaemia, translocation of bacteria, and potential perforation.
  • Systemic inflammatory response causes septic shock and multi-organ failure if untreated.

Risk factors

  • Active ulcerative colitis or Crohn’s disease.
  • Severe C. difficile or bacterial colitis.
  • Recent antibiotic use (predisposing to C. difficile infection).
  • Immunosuppression (HIV, chemotherapy, corticosteroid use).

Signs and symptoms

  • Severe abdominal pain and distension.
  • Fever and tachycardia.
  • Diarrhoea: often bloody if secondary to IBD or infection.
  • Signs of systemic toxicity: hypotension, dehydration.
  • Peritonism: suggests impending perforation.

Investigations

  • Blood tests:
    • Raised white cell count and CRP (inflammation).
    • Electrolyte abnormalities (hypokalaemia common).
    • Raised lactate (suggests ischaemia).
    • Blood cultures if sepsis suspected.
  • Imaging:
    • Abdominal X-ray (first-line): shows colonic dilatation (>6 cm) without haustral markings.
    • CT abdomen: assesses for perforation, abscess, or ischaemia.
  • Stool cultures: C. difficile toxin, other infectious causes.

Management

1. Initial Resuscitation:

  • ABCDE approach: monitor vitals and assess severity.
  • IV fluids: aggressive resuscitation to prevent shock.
  • Broad-spectrum IV antibiotics: e.g., piperacillin-tazobactam or meropenem.
  • IV steroids: if secondary to ulcerative colitis (e.g., IV hydrocortisone).
  • Bowel rest: Nil by mouth with nasogastric decompression if needed.

2. Specific Management Based on Cause:

  • IBD-related toxic megacolon: high-dose IV steroids; ciclosporin or infliximab if refractory.
  • C. difficile infection: IV metronidazole plus oral vancomycin.
  • Ischaemic colitis: supportive care; surgery if perforation.

3. Surgical Intervention:

  • Emergency colectomy: if perforation, worsening sepsis, or refractory disease.
  • Subtotal colectomy: preferred in ulcerative colitis.
GastroenterologymypanotesToxic megacolon