Introduction

Toxic megacolon is a rare but life-threatening complication of severe inflammation in the large intestine. In this condition, the colon dilates abnormally, and severe systemic toxicity can develop in the body. Colonic dilation may involve the entire large intestine or be limited to a specific segment, while systemic toxicity is a key feature of this condition. Inflammatory bowel disease (IBD) and Clostridioides difficile infection are among the most common causes of toxic megacolon. However, any severe inflammatory process affecting the colon can potentially lead to this condition.

Patients often exhibit symptoms of a serious illness affecting the entire body. Therefore, early detection and accurate diagnosis of toxic megacolon are crucial to prevent life-threatening complications and initiate appropriate treatment in a timely manner. If medical treatment does not yield the expected improvement or if serious complications—such as a perforation of the colon—develop, immediate surgery may be necessary to save the patient's life.

Cause

Toxic megacolon can develop as a complication of infectious colitis that causes severe colonic inflammation. Its primary causes include inflammatory bowel disease (IBD) and severe infections affecting the colon.

Inflammatory Bowel Disease (IBD)

Ulcerative colitis is a major type of inflammatory bowel disease (IBD). Patients with pancolitis (inflammation of the entire colon) are at higher risk of toxic megacolon, although segmental colitis can also lead to this serious complication. Toxic megacolon develops as a severe complication in approximately 5% of cases of acute severe ulcerative colitis (ASUC). Clinically, ASUC is typically identified by the presence of at least six bowel movements per day accompanied by at least one sign of systemic toxicity, such as fever, tachycardia, elevated C-reactive protein (CRP), elevated erythrocyte sedimentation rate (ESR), or hemoglobin levels below 10.5 g/dL. Crohn's disease affecting the colon can also be a significant cause of the development of toxic megacolon. For detailed information about Crohn's disease, refer to the "Crohn Disease" chapter in StatPearls.

Infectious Causes

*Clostridioides difficile* (*C. difficile*) colitis is one of the most common infectious causes of toxic megacolon. In recent years, an increase in cases of toxic megacolon associated with *C. difficile* colitis has been observed. By 1990, the rate of reported cases had risen from 0.4% to 3%. After 1990, this rate increased further to reach 4.3%. Asymptomatic colonization with *C. difficile* can be found in approximately 20% of hospitalized patients, whereas symptomatic infection is observed in about 1% of patients. A steady rise in cases of community-acquired *C. difficile* infections is being observed, accounting for approximately one-third of all *C. difficile* cases. Furthermore, a concurrent *C. difficile* infection may be found in about 50% of patients with acute severe ulcerative colitis (ASUC), underscoring the importance of timely screening for this infection in these patients.

Additionally, concomitant cytomegalovirus (CMV) colitis may be found in approximately one-third of ASUC patients who do not respond adequately to intravenous corticosteroids. In patients with HIV/AIDS, particularly in cases of disseminated CMV infection, CMV colitis can be a significant cause of toxic megacolon. Other infectious causes of toxic megacolon include the following:

Rotavirus
Salmonella spp.
Shigella
Yersinia
Campylobacter jejuni colitis
Escherichia coli
Entamoeba histolytica
Cryptosporidium
Invasive aspergillosis

Additional Causes of Toxic Megacolon

Ischemic colitis is a relatively uncommon cause of toxic megacolon. Other factors that may contribute to the development of toxic megacolon include:

Hypokalemia
Medications (eg, antimotility agents, opiates, anticholinergics, antidepressants, methotrexate)
Colonoscopy, bowel preparations, and barium enema in an inflamed colon
Neutropenic colitis
Radiation colitis
Graft versus host disease
Lymphoma of the colon
Hirschsprung disease
Behçet syndrome
Kaposi sarcoma
Hirschsprung disease
Collagenous colitis

Disease Spread

Precise information regarding the frequency of toxic megacolon in the general population is not available. Toxic megacolon can affect men and women of any age, although individuals with inflammatory bowel disease (IBD) are more likely to develop it. Approximately 48% of cases of toxic megacolon are associated with IBD.

In Crohn's colitis, toxic megacolon often develops during the early stages of the disease, before severe fibrosis has occurred. When severe fibrosis develops in the colon, its flexibility and ability to expand are reduced. The risk of toxic megacolon is higher in ulcerative colitis compared to Crohn's colitis. It is observed in approximately 8–10% of ulcerative colitis cases, whereas the rate in Crohn's colitis is around 2.3%. The primary reason for this difference is considered to be the transmural inflammation associated with Crohn's disease, which affects all layers of the intestinal wall and reduces the likelihood of excessive colonic dilation. In contrast, ulcerative colitis carries a risk of the colon dilating or expanding excessively.

Disease Process

The entire process of the development of toxic megacolon is still a subject of research and study. However, according to one potential mechanism, inflammation in the mucosal layer initiates the process. During this inflammation, inflammatory mediators and bacterial products are released, increasing the activity of inducible nitric oxide synthase (iNOS). This leads to elevated levels of nitric oxide (NO), which can result in colonic distension.

A study presented evidence supporting this mechanism, finding that levels of inducible nitric oxide synthase (iNOS) in the *muscularis propria* layer of patients with toxic megacolon were significantly higher than normal. This reinforces the possibility that nitric oxide contributes to excessive colonic distension by relaxing smooth muscle. Furthermore, inflammation within the smooth muscle can impair the functional capacity of the colonic musculature. This can result in neuromuscular dysfunction, paralysis of the bowel wall, and excessive colonic distension.

Changes in Body Tissues

Microscopic examination of colon samples removed during surgery can usually identify the cause of colitis. Pseudomembranes are typically observed in *C. difficile*-associated colitis. Colonic distension, thinning of the colon wall, and deep ulcers are key features of toxic megacolon, which can also be observed in IBD and other forms of colitis. In toxic megacolon, extensive damage, erosions, or deep ulcers may be observed in the mucosal layer. This can be accompanied by acute inflammation extending into the deeper layers of the bowel, tissue necrosis, and sloughing of the mucosa. Muscle fibers typically appear short and rounded,exhibiting abundant eosinophilic cytoplasm. Damaged or destructive changes may also be seen in the myentericplexusof the distal colon.

History and Physical

Clinical History

The patient's medical history can reveal key risk factors for toxic megacolon, including IBD—specifically ulcerative colitis and Crohn's colitis. Additionally, other conditions like diabetes and kidney failure may also be present. Information regarding the medications a patient is taking and their environment helps the doctor identify potential illnesses and select appropriate tests. Certain medications can affect the symptoms of the disease. Certain medications can affect the symptoms and severity of toxic megacolon. Corticosteroids may mask the severity of the condition, whereas anticholinergics and opioids can increase colonic dilation. The presence of these symptoms—particularly diarrhea, abdominal pain, and abdominal distension—can raise clinical suspicion of toxic megacolon. Weight loss is often observed in patients affected by toxic megacolon. This can be caused by the improper absorption of nutrients, nutrient deficiencies due to inflammation, dehydration resulting from diarrhea, reduced food intake, and vomiting.

In toxic megacolon, patients often experience severe abdominal pain, significant abdominal distension or bloating, nausea, vomiting, and diarrhea. Diarrhea is sometimes accompanied by bleeding, whereas in some cases, there is no blood. Restlessness and changes in mental status may also occur. In a study of patients with toxic megacolon associated with *Clostridioides difficile* infection, abdominal distension—along with diarrhea, restlessness, and abdominal pain—was among the most common complaints. Symptoms such as fever and severe abdominal pain can be signs of peritonitis, indicating a perforation in the intestine. If fever persists for 2–3 days during corticosteroid treatment, there may be a risk of intestinal perforation, and an immediate re-evaluation might be necessary.

Physical Examination

Physical examination often reveals symptoms such as fever, tachycardia, and hypotension, indicating a critical condition. During the physical examination, significant abdominal distension, pain or tenderness in a specific area or the entire abdomen, and diminished bowel sounds may be observed. The presence of involuntary abdominal muscle guarding or rebound tenderness, accompanied by hypotension and altered mental status, should raise immediate suspicion of colonic perforation, necessitating urgent surgical evaluation.

Evaluation

The established diagnostic criteria for identifying toxic megacolon include all the following key points:

X-ray or other radiological examinations revealing colonic dilation exceeding 6 cm, particularly in the transverse and ascending colon.

At least 3 of the following:

Fever over 38 °C
Heart rate >120 beats/min
Neutrophilic leukocytosis >10,500/µL
Anemia

At least 1 of the following:

Altered sensorium
Hypotension
Hypovolemia
Electrolyte abnormalities

Laboratory Studies

Laboratory investigations often reveal anemia and leukocytosis with an increase in neutrophils (left shift). However, neutropenia may also be observed in some immunocompromised patients or those suffering from sepsis. Metabolic acidosis may indicate ischemic colitis, while prolonged diarrhea can lead to the development of hypokalemia and metabolic alkalosis. Inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are often found to be elevated. Stool testing for *C. difficile* infection should be performed in patients suffering from acute severe ulcerative colitis (ASUC). Blood cultures may test positive in cases of sepsis. Additionally, procalcitonin and serum lactate levels may rise, and signs of coagulopathy—such as thrombocytopenia and elevated D-dimer and PT/PTT—may be observed.

Diagnostic Imaging

A plain abdominal X-ray is a key diagnostic tool for assessing the condition of toxic megacolon and monitoring its progression. It can reveal gaseous distension of the proximal colon, air-fluid levels, and the loss of normal haustral markings. The use of computed tomography (CT) is increasingly common, as it helps provide a more reliable assessment of the disease's severity. CT scans are used to detect potential complications of toxic megacolon, such as abscesses, intestinal perforation, ischemia or necrosis, and ascending pylephlebitis. CT imaging may reveal colonic wall thickening, pericolonic inflammation or fat stranding, and thickened submucosal folds. Bands of varying densities within these folds create the "accordion sign," while the differing densities of the edematous submucosa and hyperemic mucosa can produce the "target sign." An abdominal ultrasound scan can also be used, but it is of limited utility in identifying toxic megacolon, and the results are often inconclusive.

Colonoscopy

During toxic megacolon, the risk of colonic perforation increases; therefore, performing a colonoscopy is not considered safe. However, proctoscopy or sigmoidoscopy may be performed to assess severe acute colitis caused by IBD or *C. difficile* infection. During these procedures, minimal or no air is insufflated while examining the rectum and distal sigmoid colon. In some cases, CMV infection can be detected through this examination, although CMV can also affect the more proximal sections of the colon.

Treatment / Management

Appropriate medical management of the underlying cause of colitis plays a pivotal role in treating toxic megacolon. Additionally, supportive care is provided to prevent or timely detect complications such as intestinal perforation, sepsis, and other serious issues. Correcting electrolyte imbalances, replenishing fluids, and managing symptoms are crucial components of effective medical management.

Medical Management

Medication proves effective in approximately 50% of patients. If there is a risk of sudden deterioration, the patient may be admitted to the Intensive Care Unit (ICU) for close monitoring. The patient should be hydrated by administering intravenous (IV) fluids containing electrolytes, based on laboratory test results. Unless oral administration of medication is necessary, the patient may be kept from consuming any food or drink. However, as the condition improves, feeding can be gradually reintroduced, helping to restore the normal gut microbiota. All medications that could precipitate or aggravate this condition should be discontinued. Electrolytes, CBC (including WBC differential), and a plain abdominal X-ray should be performed twice daily until the clinical condition stabilizes. Once stability is achieved, these tests may be repeated on a daily basis.

The use of medications that exacerbate the condition—particularly opioids and anticholinergic agents—should be discontinued. Patients should be administered broad-spectrum antibiotics, given the increased risk of sepsis and intestinal perforation, especially if an infection is suspected. If CMV infection is suspected, treatment with ganciclovir may be initiated. Oral vancomycin (500 mg four times daily) and IV metronidazole (500 mg three times daily) can be used to treat *C. difficile* infection. If administering oral vancomycin is not possible due to ileus, 500 mg of vancomycin may be administered via rectal enema as an alternative.

Intravenous (IV) corticosteroid treatment should be initiated as soon as possible in patients with severe acute ulcerative colitis. The recommended regimen is typically 100 mg of hydrocortisone IV every 6 hours or 60 mg of methylprednisolone daily for approximately 5 days. Using higher doses is unlikely to provide additional therapeutic benefit. Infliximab may be used as second-line therapy for patients with ASUC, Crohn's colitis, or indeterminate colitis complicated by toxic megacolon who do not show adequate improvement with IV corticosteroids. Treatment response can be assessed using indicators such as persistent loose stools, hypoalbuminemia, and elevated CRP or ESR levels. If infliximab is not tolerated, cyclosporine can generally be used as an alternative treatment for refractory ASUC; however, it is not a standard option for Crohn's disease or indeterminate colitis.

Surgical Management

It is not possible to predetermine exactly when surgery should be performed in patients with toxic megacolon. If the patient's condition deteriorates, or if severe bleeding or intestinal perforation occurs, surgery can be a life-saving intervention. However, some studies indicate better outcomes in patients who undergo surgery immediately after being diagnosed with toxic megacolon. On the other hand, according to some studies, the risk of death may be relatively higher in patients over the age of 65. Therefore, surgeons, internists, hospital-based physicians, and gastroenterologists should collaborate to regularly monitor the patient's condition.

Inflammatory bowel disease

In cases of toxic megacolon associated with IBD, surgery is considered when treatment with infliximab or cyclosporine—administered after three days of IV corticosteroids for severe or fulminant colitis—proves ineffective. Similarly, surgery may be required if toxic megacolon develops while the patient is already undergoing treatment for severe colitis with these medications. It is not advisable to unduly delay surgery in patients receiving steroid treatment, as signs of disease progression may not be clearly evident.

The currently preferred surgical treatment is subtotal colectomy with end ileostomy. Wherever possible, the pericolonic mesentery and the IMA are preserved. A long rectal stump is left behind, which can be managed as a Hartmann's pouch, by subcutaneous placement of the closed rectal stump, or as a mucous fistula. Emergency surgery can be performed using laparoscopic techniques by experienced surgeons, although open surgery is generally preferred in such cases. The mortality rate associated with the surgery generally ranges between 2% and 8%, but it can rise to 40% or higher in the event of a colon perforation.