Overview
Toxic megacolon describes severe dilation of the colon (megacolon) accompanied by features of systemic toxicity, such as shock (toxic). Inflammation and damage to the colon wall are thought to lead to damage to the musculature and neurovascular supply, leading to paralysis of the affected segment and loss of smooth muscle tone, leading to dilation.
Causes
- Inflammatory bowel disease (IBD), particularly ulcerative colitis (UC) – the most common cause
- Clostridioides difficile infection
- Colonic ischaemia
- Diverticulitis
- Volvulus
- Immunosuppression – due to the increased risk of cytomegalovirus infection
- Antidiarrhoeal drugs (e.g. loperamide)
Presentation
Patients tend to present with abdominal symptoms and signs of shock:
- Abdominal pain and tenderness
- Abdominal bloating
- Abdominal distention
- Fever
- Tachycardia
- Hypotension
Differential Diagnoses
Acute mesenteric ischaemia
- Patients may have risk factors, such as atrial fibrillation or coronary artery disease
- Although this can present with diffuse and severe abdominal pain and systemic upset, abdominal distention is typically absent
Investigations
- Full blood count:
- May show leukocytosis suggesting infection
- Acute blood loss or chronic disease may cause anaemia
- Urea and electrolytes (U&Es):
- May show electrolyte abnormalities such as hypokalaemia secondary to diarrhoea
- Serum lactic acid:
- May be elevated in bowel ischaemia
- Stool sample testing:
- May show evidence of Clostridioides difficile infection
- Abdominal x-ray:
- Often performed as an initial investigation
- Shows a dilated bowel
- The normal sizes can be remembered using the ‘3-6-9’ rule:
- Small bowel <3 cm
- Large bowel: <6 cm
- Caecum: <9 cm
- Chest x-ray:
- Can rule out bowel perforation, which may show free air under the diaphragm
- Abdominal CT:
- Can help with diagnosis and shows a dilated colon with a loss of normal haustral markings
Management
Overview
Management often involves:
- Making the patient nil-by-mouth
- Resuscitation with IV fluids
- Broad-spectrum IV antibiotics, particularly if an infective cause is suspected
- For IBD: IV corticosteroids are often used
- Surgery – usually considered after 72 hours of medical management
- This is usually an abdominal colectomy with end-ileostomy
- This may result in the patient requiring a temporary or permanent stoma
Complications
- Perforation
- Sepsis
Prognosis
- Toxic megacolon is associated with high mortality and morbidity rates
- Factors such as increased age and the presence of other comorbidities such as heart failure are associated with a poorer outcome
