What are the diagnostic criteria and management for toxic megacolon?

Diagnostic Criteria for Toxic Megacolon

Toxic megacolon is diagnosed by the combination of radiographic colonic distension >5.5-6 cm (particularly in the transverse colon), clinical signs of systemic toxicity, and an underlying inflammatory or infectious etiology. 1, 2

Radiographic Criteria

• Plain abdominal radiograph showing transverse colonic dilation >5.5 cm is the most established radiological definition and remains an acceptable first-line study 1, 2
• Some sources define the threshold as >6 cm for total or segmental colonic distention 2, 3
• The transverse colon is the critical area to measure, as this is where greatest dilation and highest perforation risk occur (unlike mechanical obstruction where the cecum is most vulnerable) 2, 3

Clinical Criteria for Systemic Toxicity

You must document signs of severe systemic inflammatory response, including: 1, 4

• Fever >38.5°C 1
• Tachycardia 4
• Hypotension or hemodynamic instability 1, 4
• Altered mental status 4
• Rigors (uncontrollable shaking followed by temperature rise) 1
• Signs of distributive/septic shock 1

Laboratory Markers of Severity

While not absolute diagnostic criteria, these support the diagnosis and indicate severity: 1

• Marked leukocytosis (>15-20 × 10⁹/L) 1
• Marked left shift (band neutrophils >20%) 1
• Rise in serum creatinine (>50% above baseline) 1
• Elevated serum lactate 1
• Hypoalbuminemia (<25 g/L) 1

Underlying Etiology Required

The diagnosis requires documented inflammatory or infectious cause: 2, 5

• Inflammatory bowel disease (ulcerative colitis or ileocolonic Crohn's disease) - most common historically 2, 5
• Clostridium difficile colitis - increasingly common etiology 5, 6
• Other infectious causes: Salmonella, Shigella, Campylobacter, CMV 5

Advanced Imaging Indications

CT scanning should be performed when perforation is suspected, when plain films are equivocal, or when the patient shows signs of hemodynamic instability 1, 4. CT provides critical additional information: 1, 2

• Detection of perforation (free or contained) 1, 2
• Abscess formation 1, 2
• Ascending pylephlebitis/mesenteric venous thrombosis 1, 2
• Colonic wall thickening and pericolonic fat stranding 1

Endoscopic Findings (When Performed)

• Pseudomembranous colitis is virtually diagnostic of C. difficile-associated toxic megacolon 1
• Endoscopy should be performed cautiously due to perforation risk 1

Critical Diagnostic Pitfalls to Avoid

• A negative CT does not exclude perforation or other complications - combine imaging with clinical assessment and laboratory findings 1
• Do not miss C. difficile as the underlying cause - test all patients 4, 6
• Persistent fever after 48-72 hours of steroid therapy strongly suggests local perforation or abscess formation requiring immediate CT 2, 4
• Progressive colonic dilation on serial imaging is an indication for urgent surgical intervention, even without frank perforation 2, 3

Monitoring Requirements

• Daily abdominal radiographs to track colonic diameter progression 6
• Serial clinical assessments for worsening systemic toxicity 4
• Immediate surgical consultation is mandatory at diagnosis - this is a medical-surgical emergency requiring coordinated management from admission 3, 4