Toxic Megacolon

What happens in toxic megacolon

Severe inflammation spreads through the full thickness of the colon wall, damaging the muscle and nerves that move the bowel. The colon stops contracting, fills with gas and fluid, and dilates. Inflammatory chemicals and bacterial toxins enter the bloodstream, causing fever, a fast heart rate and, in severe cases, shock. The thinned wall can tear (perforate), releasing stool into the abdomen.

Causes

Triggers in someone with colitis

• antidiarrheal medicines (loperamide)
• opioids and anticholinergic medicines, which slow the bowel
• low potassium or magnesium
• barium enema or colonoscopy during severe active colitis
• abrupt stopping of steroids or other IBD treatment

Symptoms

• severe abdominal pain and a swollen, tender, tight belly
• fever, often over 38.5 °C (101.3 °F)
• fast heart rate
• bloody diarrhea, which may paradoxically decrease as the colon stops moving
• dehydration, low blood pressure, dizziness
• confusion or altered alertness
• reduced or absent bowel sounds

Steroids and painkillers can mask some signs, so doctors monitor closely.

Diagnosis

Commonly used criteria require:

• X-ray or CT showing colon dilation greater than 6 cm, plus
• signs of systemic toxicity, such as fever over 38.6 °C (101.5 °F), heart rate over 120, raised white cell count or anemia, and at least one of dehydration, altered mental state, electrolyte imbalance or low blood pressure

Other tests:

• stool tests for C. difficile and other infections
• blood tests: blood count, electrolytes, albumin, lactate, inflammatory markers
• CT scan to assess the colon wall, abscesses or perforation

Colonoscopy is usually avoided because of the high risk of perforation.

Treatment

Treatment takes place in hospital, often in intensive care, with daily assessment by gastroenterologists and surgeons.

Medical treatment

• bowel rest: nothing by mouth, sometimes a nasogastric tube
• IV fluids and correction of electrolytes (potassium, magnesium)
• stop antidiarrheals, opioids and anticholinergics
• for IBD: high-dose IV corticosteroids; rescue therapy with infliximab or cyclosporine if no response in 3 to 5 days
• for C. difficile: oral vancomycin (or via the rectum if the bowel is not moving) plus IV metronidazole, and stopping other antibiotics where possible
• broad-spectrum antibiotics if perforation or sepsis is suspected
• blood clot prevention: people with severe colitis are at high risk of clots
• repositioning maneuvers (rolling or lying prone) can help release gas

Surgery

Surgery (usually a subtotal colectomy with an ileostomy) is needed if:

• the colon perforates
• there is uncontrolled bleeding
• the patient worsens or does not improve within 24 to 72 hours of intensive medical treatment
• the colon keeps dilating

Delaying necessary surgery increases the risk of death. After recovery, some people with ulcerative colitis can later have reconstructive surgery (ileal pouch) to avoid a permanent stoma.

Outlook

With early recognition and treatment, most patients survive. Mortality rises sharply if perforation occurs. Patients with ulcerative colitis who recover medically remain at high risk of needing colectomy later.

Prevention

• seek prompt care for severe colitis flares
• avoid antidiarrheals and opioids during a severe flare unless a doctor advises them
• use antibiotics only when needed to reduce the risk of C. difficile infection
• treat C. difficile promptly

Frequently asked questions

What is toxic megacolon?

It is a rare, life-threatening condition in which the colon suddenly becomes very dilated and stops working, while the patient becomes severely ill with fever, fast heart rate and signs of toxicity. It usually results from severe colitis.

What causes toxic megacolon?

The most common causes are ulcerative colitis, Crohn's colitis and C. difficile infection. Other infections and ischemic colitis can also cause it. Antidiarrheal medicines, opioids and low potassium can trigger it during severe colitis.

What are the symptoms of toxic megacolon?

Symptoms include a painful, swollen belly, fever, a racing heart, dehydration, confusion and low blood pressure. Diarrhea may decrease as the colon stops moving, which is a warning sign rather than an improvement.

How is toxic megacolon treated?

It is treated in hospital with bowel rest, IV fluids, correction of electrolytes, IV steroids for IBD or specific antibiotics for C. difficile, and close monitoring. Surgery to remove the colon is needed if there is perforation or no improvement within a few days.