What Is Toxic Megacolon

  • Geethaa Sathveekan Bachelor of Medicine, Bachelor of Surgery - MBBS, Queen Mary University of London


While people might be aware of inflammatory conditions that affect the bowels, not many know about the complications of these illnesses, like toxic megacolon (TM). This article will provide relevant information about TM and what it means for those affected. 

Definition of toxic megacolon

TM is a rare and potentially life-threatening complication of colonic inflammation (colitis).1 It is characterised by full or partial non-obstructive widening (distension) of the colon and is often associated with symptoms of systemic toxicity (sepsis).1 Systemic toxicity differentiates TM from other causes of colonic distension. 

In colitis, inflammation initially occurs in and is contained within the mucosa, the first layer of the colon. However, continuous and prolonged inflammation can spread to deeper muscular layers (which is known as transmural inflammation), causing injury and weakness of the colon.1,2 This process subsequently leads to colonic wall thinning and reduces its ability to contract normally, causing the build-up of toxic substances.2 The colon can rupture due to weakness and these toxic substances can leak into the bloodstream causing systemic illness. If left untreated, TM can cause multi-system organ failure and subsequently, death.


While TM is most associated with inflammatory bowel disease (IBD), specifically ulcerative colitis (UC), it can be caused by any condition that leads to colonic inflammation including infections and the use of certain drugs.1,3

Underlying conditions:


- Ulcerative Colitis: UC is an autoimmune condition which results in chronic inflammation and ulceration of the rectum and anus. Symptoms include diarrhoea, bloody stool, abdominal pain, and feeling of incomplete bowel evacuation.2 It is the leading cause of toxic megacolon, accounting for about 8-10% of cases.1

- Crohn’s Disease: Like UC, Crohn’s disease is an autoimmune condition, causing similar symptoms. However, unlike UC, it affects all parts of the digestive system, which extends from the mouth to the anus. TM is more likely to occur in the early stages of Crohn’s disease.2


Organisms like bacteria, viruses and parasites are responsible for bowel infections which can lead to food poisoning (gastroenteritis) and stomach flu. In severe cases, these infections can cause colitis, which is a precipitating factor of TM. Causative organisms include Shigella, Salmonella, Campylobacter, E. coli, Cytomegalovirus (especially in people with HIV), Rotavirus, Cryptosporidium, etc.3,4 

Clostridium difficile (a bacterium) is the organism most commonly associated with a type of infective colitis called pseudomembranous colitis, especially after recent antibiotic use.4 

Ischaemic colitis: 

Reduced blood flow (ischaemia) to the bowel can lead to colitis.3 If untreated, this can affect normal bowel function and potentially trigger TM.


Underlying conditions like electrolyte imbalances (e.g., low blood potassium levels) and in rare cases, colon cancer can lead to TM.2,3


Drug treatments including opioids, antimotility agents, anticholinergics, antidepressants, and NSAIDs can precipitate TM.1,2

Diagnostic procedures: 

Barium enemas, colonoscopies, and pre-colonoscopy bowel prep might cause TM.1,2

Risk factors

TM is more likely to occur if you have the following risk factors:4

- IBD (UC and Crohn’s)

- Diabetes 

- HIV/Aids 

- Kidney failure

- Heart failure 

- Use of certain medications like opioids, antimotility agents, anticholinergics, antidepressants, and NSAIDs.4

Clinical presentation 

Symptoms of TM are non-specific and may be present in other conditions. However, regardless of which symptoms are present, urgent medical attention is required. Symptoms include:5,7

- Abdominal pain

- Swollen abdomen and bloating

- Reduced bowel sounds

- Nausea and vomiting

- Diarrhoea

- Malaise

- Bloating

- Altered mental status

- Dehydration

- Fever

- Fast heart rate

- Dizziness

- Low blood pressure


Your doctor will usually make a diagnosis of TM based on a combination of your history, clinical presentation (signs and symptoms), imaging (X-ray or CT scan) and laboratory investigations.

You will be asked about your complete medical history and a physical exam will be conducted. It is very important that you tell your doctor about any medical conditions you have and any medications you might be taking. The physical examination might show a distended abdomen, reduced bowel sounds and vital signs suggestive of systemic illness, including low blood pressure, fast heart rate, and fever.5,6 The diagnostic criteria include:

- Radiographic evidence of colonic dilation of greater than 6 cm (usually confirmed via X-ray)1,2 AND,

- At least three of the following:1,2

• Heart rate faster than 120 beats/min

• Low red blood cell count (anaemia)

• Fever greater than 380C

• High white blood cell count 

- At least one of the following:1,2

• Low blood pressure 

• Dehydration 

• Electrolyte disturbances 

• Altered mental status

Blood tests often show increased inflammatory and infection markers and electrolyte imbalances such as low blood potassium, and low blood protein.5 If readily available, X-rays are the first choice for imaging. Otherwise, CT scans and less commonly, abdominal ultrasounds can be used. While colonoscopies are used to diagnose conditions causing bowel inflammation, they are not necessary to diagnose TM, especially due to a high risk of bowel perforation.6


If left untreated or managed inappropriately, TM can lead to:1,2

- Bowel perforation 

- Bowel rupture 

- Inflammation of the inner lining of the bowel (peritonitis)

- Collection of pus in the colon (abscess)

- Abdominal compartment syndrome

- Organ failure and sepsis

These complications can eventually lead to death.


TM is a rare medical emergency that requires immediate attention in a hospital setting involving a multi-disciplinary team of healthcare professionals. TM cannot be managed without proper medical supervision at home. Treatment aims to correct any underlying cause, manage symptoms and prevent complications. Management can be classified into:

- Medical management: 

  • stop medications which can precipitate TM
  • start IV fluids (which contain electrolytes) for rehydration and electrolyte correction 
  • antibiotics to treat any infections 
  • non-opioid analgesia for pain relief (to stop bowel inflammation)
  • nasogastric tube feeding (to promote bowel rest and healing)6,7 

Admission to ICU might be indicated if there is a sudden deterioration.5

- Surgical management: Surgery is not always necessary to manage TM. However, surgeons will be involved from your initial presentation in case there are complications, and it is eventually needed.2 If indicated, surgery usually involves partially or completely removing the colon. Afterwards, you might have a temporary or permanent ileostomy or colostomy.3 An ileostomy connects the lowest part of your small bowel, and a colostomy connects the large bowel to an opening created in your tummy. This opening is connected to a bag and allows faeces to be emptied. Support will be provided to help with adjustment to ileostomy use.


About 93% of patients with TM survive and make a good recovery. In people with IBD, the mortality rate is low, usually about 0-2%.1,2 However, bowel perforation can worsen the prognosis and increase the likelihood of death by approximately 3 to 5 times.2 Other factors like an age greater than 65 and late surgical intervention can also lead to poor outcomes.1,2


Although TM is a relatively rare disease, it is an important condition to know about, especially if you have IBD or other bowel conditions. To aid understanding, in addition to reading articles like this, it is important to talk to your doctor about precipitating factors, symptoms to be aware of and when to seek medical attention. This is imperative as early detection and treatment significantly reduces mortality rates. 

Prevention lies in managing underlying conditions effectively, ensuring the safe use of medications, and seeking timely medical attention when symptoms arise.7 With the right medical care and support, individuals diagnosed with TM can hope for improved quality of life and reduced risk of life-threatening complications. Awareness, education, and early intervention are key to mitigating the impact of this challenging condition


In conclusion, toxic megacolon is a severe medical condition characterized by the dangerous dilation of the colon and systemic toxicity. It primarily occurs as a complication of underlying conditions such as inflammatory bowel disease or infections, often exacerbated by specific triggers or medications. Early recognition and diagnosis are crucial, as toxic megacolon can lead to life-threatening complications, including perforation of the colon, sepsis, and organ failure.


This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

Get our health newsletter

Get daily health and wellness advice from our medical team.
Your privacy is important to us. Any information you provide to this website may be placed by us on our servers. If you do not agree do not provide the information.

Oluwagbemisola Jemimah Arolasafe

MBChB, M.Sc Biomedical Informatics, and B.Sc Biochemistry (Hons)

Oluwagbemisola works as a doctor within the NHS, an experience which continually provides significant exposure to medical, surgical and psychiatric specialities.

She has a broad range of interests but is mostly passionate about mental health and health inequalities, and the intersection between the two in society. She enjoys writing creatively and for several years, has combined that with her training as a medical doctor through writing medical articles.

Oluwagbemisola is currently working on implementing evidence-based recommendations to improve breast cancer screening uptake in BAME communities and people with learning disabilities in a borough within the West Midlands.

Leave a Reply

Your email address will not be published. Required fields are marked *

my.klarity.health presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
Klarity is a citizen-centric health data management platform that enables citizens to securely access, control and share their own health data. Klarity Health Library aims to provide clear and evidence-based health and wellness related informative articles. 
Klarity / Managed Self Ltd
Alum House
5 Alum Chine Road
Westbourne Bournemouth BH4 8DT
VAT Number: 362 5758 74
Company Number: 10696687

Phone Number:

 +44 20 3239 9818