Toxic Megacolon

Toxic megacolon is acute nonmechanical colonic dilatation associated with severe systemic toxicity.

It most often complicates ulcerative colitis, Crohn colitis or severe infectious colitis, particularly Clostridioides difficile.

Colonic diameter is generally at least 5.5 to 6 cm, accompanied by systemic toxicity. Progressive mural inflammation and loss of smooth muscle tone place the colon at high risk of perforation.

Patients are acutely ill with abdominal distension, pain, diarrhoea or bloody stool and systemic toxicity.

Concerning findings include fever, heart rate above 120 beats/min, hypotension, dehydration, altered mentation and electrolyte disturbance.

A sudden decrease in abdominal pain or diarrhoea does not necessarily indicate improvement. It can accompany worsening colonic paralysis or perforation.

Plain abdominal radiography: rapidly demonstrates colonic dilatation and permits serial comparison.

CT abdomen: use when perforation, abscess or another complication is suspected and the patient is stable enough for imaging.

Avoid full colonoscopy and aggressive bowel preparation because insufflation can precipitate perforation.

Admit to a monitored setting and involve colorectal surgery immediately.

Stop opioids, anticholinergic agents, antimotility drugs and other medications that worsen colonic dilatation.

Correct fluid, potassium, magnesium and other electrolyte deficits. Provide pharmacological venous thromboembolism prophylaxis unless contraindicated.

If ulcerative colitis is the underlying cause and perforation or uncontrolled infection is not present:

Methylprednisolone 60 mg IV daily

or

Hydrocortisone 100 mg IV every 6 hours.

Do not continue ineffective steroid treatment while the patient deteriorates.

Toxic megacolon with worsening systemic toxicity, perforation, uncontrolled haemorrhage, increasing dilatation or failure of rapid medical improvement requires urgent total abdominal colectomy with end ileostomy, leaving the rectum for later staged management.

When fulminant Clostridioides difficile infection is responsible, treat with:

Vancomycin 500 mg orally or through nasogastric tube every 6 hours

plus

Metronidazole 500 mg IV every 8 hours.

With major ileus preventing effective colonic drug delivery, add rectal vancomy according to local critical care protocol.

Do not delay colectomy in a deteriorating patient because antimicrobial or immunosuppressive rescue is being attempted.