What Is Toxic Megacolon?

Medically Reviewed by Minesh Khatri, MD on May 28, 2023
4 min read

It starts when irritation or infection inflames your colon, the last section of your digestive tract. This alone doesn’t mean you have toxic megacolon, but it’s the first step. It’s only when all or part of your colon expands to wider than normal (your doctor will say it’s dilated), and starts to push toxic substances throughout your body (this is called systemic toxicity), that you have the condition. It requires care right away because it could lead to tears in your digestive tract, blood loss, and a possibly deadly condition called sepsis, in which your body becomes inflamed as a reaction to the toxins in it.

Inflammatory bowel disease, or IBD, is the most common initial cause of toxic megacolon. There are two main forms: ulcerative colitis (UC) and Crohn’s disease. Both these conditions involve an overreaction by your immune system. They inflame the colon and can cause belly pain, weight loss, diarrhea, bloody poop, nausea, joint pain, fever, and skin rashes.

But UC is limited to the innermost layer of the colon, while Crohn’s can inflame all the layers of your bowel and is not limited to the colon, but can cause ulcers anywhere in your digestive system, from your mouth to your anus. And in Crohn’s, healthy sections of intestine typically alternate with inflamed areas, while UC doesn't cause "skip lesions" but continuous lesions through the entire colon.

Note that IBD is not the same as irritable bowel syndrome, or IBS, though it could have similar symptoms. IBS has to do with the muscles and nerves that control the bowel, as opposed to the bowel itself, so there’s no inflammation or ulcers. It isn’t usually related to toxic megacolon.

It’s less common, but infection from a virus, bacteria, or even a parasite can inflame your bowel and lead to toxic megacolon. An infection from Clostridioides difficile (C. diff) bacteria is a common cause, along with campylobacter, salmonella, and shigella. Certain illnesses or medications (like opioids and antidepressants) that lessen blood flow to your bowel might also do it.

Anyone can get it. But certain conditions, especially IBD, put you at a higher risk. In addition, it’s more likely if you have diabetes, kidney problems, a transplanted organ, or problems with your immune system.

Diarrhea, often quite serious and bloody, is common at first. You also might have a fever, dizziness, a swollen belly, and a racing heart. When your colon dilates, a classic sign of toxic megacolon, it can’t move gas through your gut. As a result, your lower belly could bloat quite a bit and may become painful and tender to the touch.

Get to a doctor ASAP if you notice these symptoms. Toxic megacolon can get serious very quickly.

Your doctor and health care team will examine you and ask about your symptoms, your health history, and any other conditions, like IBD, that tend to inflame the colon.

They may take pictures of the inside of your gut with X-rays or a CT scan to see if your colon has dilated, and do blood tests to check for infection and other possible problems.

A swollen belly -- along with other symptoms like fever over 100 degrees F, heart rate over 120, low red blood cell count, low blood pressure, and dehydration -- might point to a toxic megacolon diagnosis.

It depends how serious it is, as well as your symptoms, age, general health, and the cause of the condition.

Medication to treat the underlying condition that resulted in toxic megacolon can help. If the cause is IBD, treatment often includes steroids and an immune system drug like infliximab or cyclosporine. If it resulted from an infection, you’ll probably need antibiotics. For ulcerative colitis, your doctor might prescribe antibiotics to stop or prevent bacterial infection, and anti-inflammatories to help ease swelling in your colon.

You also might go on bowel rest, which means you may get your nutrition through a needle or a tube instead of from food. Your health care team might try to remove air from your colon with a suction tube. This is all to lessen pressure on your inflamed, dilated colon and prevent it from tearing, which is serious.

You may get fluids through a needle to prevent dehydration and low blood pressure.

Some people need surgery. The decision on when and if to have it is complex. There may be a number of things for you and your medical team to consider. If nonsurgical treatments don’t ease the condition in 2 or 3 days, you’ll likely need surgery to remove all or part of your colon. You’ll also typically go straight to surgery if it’s clear that your bowel is torn or dead, you’re bleeding internally, your colon is getting wider, or your blood is getting more toxic.

Your doctor might ask you to stop certain medications that could worsen toxic megacolon, like opioids, anticholinergics, antidepressants, and anti-diarrheals.

As long as your colon doesn’t perforate or tear, the survival rate for well-treated toxic megacolon is above 95%. Even if it does tear, the survival rate is around 80%. But some studies show that if you get toxic megacolon once and your doctor treats it without surgery, you’re more likely than others to get it again.