Toxic megacolon in ulcerative colitis: warning signs, emergency care and treatment

Ulcerative colitis is a long-term condition in which parts of the large bowel (colon) and rectum become inflamed. The NHS describes it as one of a group of conditions called inflammatory bowel disease, and says it is thought to be an autoimmune condition. For most people it follows a pattern of quieter spells (remission) and flare-ups, and most flare-ups can be managed with medicines.

Toxic megacolon is a rare complication that can arise when the inflammation becomes extensive and severe. Crohn’s & Colitis UK explains that the bowel wall thins and the colon becomes bloated with gas. NHS inform describes the same process as severe inflammation leading to trapped gas, so that the colon becomes very enlarged and can rupture.

It is not a separate disease and it is not something that happens in a mild flare. It sits at the far end of the severity range of ulcerative colitis, which is why UK sources discuss it under complications and under acute severe ulcerative colitis, usually shortened to ASUC.

Crohn’s & Colitis UK says the symptoms of toxic megacolon include a high fever with pain and tenderness in the tummy. It also says that people with a flare-up may be at risk of developing sepsis, which it describes as a life-threatening over-reaction of the immune system to an infection.

The NHS page on ulcerative colitis does not name toxic megacolon, but it sets out when to seek help during colitis. These are the same features that matter if a flare-up becomes severe.

• Very bad diarrhoea or bloody diarrhoea.

• A high temperature, or feeling hot, cold or shivery.

• A fast heartbeat.

• Being unable to fart or poo.

• Severe tummy pain, which the NHS puts in the “call 999 or go to A&E” category.

• A lot of bleeding from the bottom, large blood clots, or vomiting blood or sick that looks like coffee grounds.

The NHS advises asking for an urgent GP appointment or contacting NHS 111 if you have symptoms of ulcerative colitis together with very bad or bloody diarrhoea, a high temperature, a fast heartbeat, or if you cannot fart or poo. If you already have a diagnosis and are having a severe flare-up, it says you can also contact your care team.

It advises calling 999 or going to A&E for severe tummy pain, non-stop bleeding from the bottom, a lot of blood or large clots when you poo, or vomiting blood. It also says not to drive yourself to A&E, to ask someone to take you or call 999, and to bring your medicines.

Crohn’s & Colitis UK is direct on this point: contact NHS 111 straight away if you think you have signs of a perforation or toxic megacolon. A perforation is a rupture of the bowel, which creates a hole that bowel contents may leak through. The charity describes perforations as very rare but very serious, and lists severe tummy pain that is present all the time, a high fever, and feeling or being sick as possible symptoms.

The cause of ulcerative colitis itself is not known, according to the NHS. It says anyone can get it, but you might be more likely to if someone in your family has it or if you used to smoke. Toxic megacolon is a consequence of very active inflammation rather than a separate trigger, so the people most at risk are those whose colitis is extensive and severe.

Crohn’s & Colitis UK lists possible flare-up triggers including changes to medicines, ongoing stress, gut infections and taking non-steroidal anti-inflammatory medicines (NSAIDs) such as ibuprofen. The NHS likewise advises people with ulcerative colitis not to take NSAIDs such as ibuprofen or aspirin unless prescribed by a doctor.

One avoidable factor is the choice of medicines to relieve symptoms. Crohn’s & Colitis UK explains that anti-diarrhoeal drugs such as loperamide (Imodium) and diphenoxylate (Lomotil) slow the muscle movements in the gut, and that they should not be used during a flare-up because they increase the risk of toxic megacolon. It says they should only be taken if your IBD team has said it is fine. If you have colitis and are tempted to reach for an over-the-counter stopper during a flare, check with your IBD team or pharmacist first.

The NHS says ulcerative colitis is usually diagnosed in hospital by a gastroenterologist, and that tests can include blood tests, a stool sample, scans such as X-ray, CT or ultrasound, and a colonoscopy with a biopsy. For someone admitted with a severe flare, the hospital team will use their examination and these kinds of tests to judge how severe the colitis is and whether the colon has become enlarged.

Crohn’s & Colitis UK groups severity as mild, moderate or severe. Severe colitis is described as six or more poos each day with visible blood, and blood and poo tests that show inflammation. ASUC includes all of those features plus signs that the body is being significantly affected, such as a fever or increased heart rate.

Specific measurements and imaging thresholds used by the hospital team are clinical decisions and are not set out in the patient sources used for this page, so they are not listed here.

For acute severe ulcerative colitis, Crohn’s & Colitis UK says you will stay in hospital and may be given a high dose of steroids through a drip into a vein. If steroids have not worked after three days, you may be offered infliximab or ciclosporin. If those have not worked after seven days, it says surgery may be necessary.

The NHS notes that emergency surgery may be needed for a very bad flare-up. The operation is a colectomy, in which part or all of the large bowel is removed. It stops the ulcerative colitis coming back but means the body needs a different way to pass out poo, either an ileostomy (the small bowel connected to a hole in the tummy, with poo collected in a bag) or an ileo-anal pouch (a “J pouch”) made from part of the small bowel.

Crohn’s & Colitis UK lists a perforation or toxic megacolon among the severe complications for which surgery may be offered. It also gives a longer-term picture: around 7 in 100 people with colitis will need major surgery to remove their colon in the first five years after diagnosis, and around 10 in 100 within 10 years, and fewer people are needing surgery than 20 years ago.

The NHS describes ulcerative colitis as lifelong and unpredictable, with treatment and lifestyle changes that should help and a lot of support available. It suggests taking prescribed medicines even when you feel well, staying hydrated if you have diarrhoea, having vaccinations you are offered because some colitis medicines make infections more likely, and going to bowel cancer screening appointments when invited.

Many people find it helpful to agree a plan with their IBD team about what to do if symptoms flare. Crohn’s & Colitis UK suggests asking your IBD team how best to alert them if you become unwell, for example by emailing with “Flare-up” in the subject line, and it advises contacting your GP or out-of-hours service if you cannot reach them.

The NHS says it is common to feel stressed, anxious or embarrassed about symptoms and mentions NHS talking therapies, which you can refer yourself to without a GP referral. Charities such as Crohn’s & Colitis UK and the Ileostomy and Internal Pouch Association offer information and peer support, including for people facing or living with a stoma or pouch.

Severe colitis flare-ups are managed through emergency and inpatient NHS services, because treatment depends on hospital monitoring, intravenous medicines and access to surgeons at short notice. Routes in are NHS 111, an urgent GP appointment, the IBD team, or A&E.

Some people also see a private gastroenterologist for routine follow-up or a second opinion between flare-ups, but the emergency situation described on this page is normally dealt with in an acute hospital whichever way the earlier care was arranged.