Introduction

Toxic megacolon (TM) is known as a complication of inflammatory bowel disease (IBD) and can be defined as an infectious cause of the colon due to partial or total non-obstructive colonic dilation and systemic toxicity. There are high associations with morbidity and mortality, and surgical intervention is a requirement in most cases. However, an accurate history and a physical examination are necessary. A sigmoidoscopy and plain radiographs of the abdomen will increase awareness of the condition and facilitate the diagnosis of TM.

TM is a potentially life-threatening condition and has a feature of acute colonic dilatation that is more than six cm in diameter. Under radiological examination in severe cases of colitis, a loss of haustration can be observed. TM does possess a low prevalence rate; however, the outcomes have proven to be unsatisfactory (hospital mortality 7.9%).

Epidemiology

The figures of TM prevalence are under-reported, but the rate of prevalence rate increases with age.

The most common cause of hospital admission is:

• IBD (51%)
• Septicemia (10.2%) 
• Intestinal infections (4.1%)

Researchers have discussed results from studies to are conflicting. For example, the incidence of TM is higher in patients with Ulcerative Colitis (UC) (8-10%) when compared to Crohn’s disease (CD) (2.3%). Whereas other data from studies has shown the incidence in CD to be higher in UC (4.4% to 6.3% in CD) when compared to UC (1% to 2.5%).     

The incidence due to Clostridium difficile (C. diff) was estimated to be 0.4% to 3% before the 1990s, but this increased to 4.3% after the 1990s.

Factors that have led to an association with high mortality are:

• Age range of 40 years plus
• Female gender 
• Hypoalbuminemia
• Acidosis
• High blood urea nitrogen levels 

Contrastingly, the mortality in patients with TM is variable. Historic figures of 1976 for TM were 27% (medically managed cases) but as low as 19% (in surgically managed cases). This figure showed a decline from 0% to 2% in patients with IBD. It is suggested that early identification and an intensive management care plan may have contributed to the reduced incidence and mortality of TM in IBD. On the other hand, patients who have a fulminant infection require surgical intervention (20% of cases). Which carry a mortality rate of 35% to 80%. Colonic perforation is known to be the most crucial predictor of mortality as 44% of patients underwent emergency colectomy after colonic perforation in comparison to 2% of patients who had no perforation and did not require the procedure.        

Etiology 

UC and CD hold a crucial aetiology for TM. This suggests that any inflammatory condition of the colon could be susceptible to TM. TM is a rare and lethal complication that causes inflammation of the colon.

Isolated cases of TM have been reported from 1933 to 1941 by The Massachusetts General Hospital. And in 1956, researchers described TM as a ‘toxic aganglionic megacolon’. This is about the pathogenesis of TM, with a description of a destructive change in the nerve plexus in the distal colon.

Pathogenesis

Although the mechanism in the development of TM is yet to be understood, the changes in the incolonic response to chemical mediators lead to a defective contracted smooth muscle. Basal pressure of the colonic lumen is also lowered, which plays an important role in the development of TM.

Clinical manifestations

TM can affect both genders and all ages, but complications can persist earlier in patients with IBD. TM can occur in 5% of a severe attack of UC. Around 50% of patients who present symptoms of TM also develop this complication in the first three months of an IBD diagnosis. TM commonly occurs in patients who suffer from pancolitis. The most common symptoms that patients with TM present are: 

• Hypotension
• tachycardia
• Bloody diarrhea  
• Fever
• abdominal tenderness
• sluggish bowel sounds
• Abdominal pain
• Progressive systemic toxicity including: leukocytosis, metabolic alkalosis and electrolyte derangements

The consumption of strong analgesics may conceal the signs and symptoms of TM. Free perforation can transpire without dilating the colon. Although this is a rare complication that develops in around 1% of patients with UC but without TM. The usual presentation of peritonitis may be absent, mainly due to the masking effect of steroid therapy.

Another symptom of TM  is hepatic dullness, particularly in patients with severe colitis. These patients may be taking part in steroid therapy due to presenting with free perforation and not showing the typical signs of peritonitis. For this reason, a daily X-ray of the abdomen is suggested.        

Diagnosis

The diagnostic criteria of TM include:

1. A radiographic image of colonic dilation of more than 6 cm (in the transverse colon).

2. Any of the following symptoms:

• A temperature (greater than 38.8°C) 
• Tachycardia (greater than 120 beats/min)
• Leukocytosis (greater than 10.5 × 103/μL) 
• Anemia

3. Any of the following symptoms:

• Hypotension
• Hypovolemia
• Electrolyte disorders
• Altered mental status

The primary diagnostic purpose of TM is to diagnose the condition and its underlying aetiology. However, as ‘megacolon’ is defined radiographically by a maximum diameter of 6cm, imaging diagnosis is needed. Computed tomography of the abdomen will aid in establishing a contrast with the complication. This will potentially diagnose and evaluate for complications that require immediate surgery.    

Baseline and serial abdominal X-rays will support the progression of colonic dilatation. 

Typical features that may be observed in the radiography are:

• A dilated transverse or the right colon (greater than 6 cm). 
• Deep mucosal ulcerations 
• Segmental colonic wall thinning
• Air fluid levels with an abnormal haustral pattern     
• Nodular pseudo polyps on an X-ray radiologic examination. 

Some common laboratory abnormalities are associated with TM, these include:

• Leukocytosis with prominent neutrophilia 
• Anaemia from gastrointestinal blood loss
• metabolic alkalosis secondary to volume depletion
• Hypoalbuminemia
• Hypokalemia
• Elevated inflammatory markers including ESR and CRP

A complete colonoscopy is significantly risky in patients with TM as it can be a cause of colonic perforation. A limited endoscopic examination (without bowel preparations) is recommended, which includes proctoscopy or sigmoidoscopy. These are safer options in comparison to a complete colonoscopy and useful to diagnose aninflammatory diseases.

Summary

TM is a potentially fatal condition and can be defined as an acute colonic dilatation. There have been some recent advancements for the condition, particularly regarding epidemiology and its pathogenesis. The mortality rates for TM are inconsistent. This can be noted in the death rate that decreased before 1976 (27% of cases) for patients who were medically managed and those who underwent surgery (19% of cases). The in-house mortality for TM then showed a decrease from 9.2% to 6.5% in four years from 2010.      

TM is a condition that is best managed by the combined efforts of the medical and surgical team. Although medical therapy is the first point of treatment in the majority of cases. Objective measures to manage the condition should be discussed with the patient before initiating treatment. If the patient shows signs of peritonitis, haemorrhage or perforation surgery should be considered immediately.   

FAQs

1. What is the clinical presentation of toxic megacolon?

Toxic megacolon (TM) can be characterised by extreme inflammation and distention of the colon. Symptoms include: pain, a rapid heart rate and dehydration. 

2. What is the best treatment for toxic megacolon?

• IV fluids may be suggested. This will ensure patients with TM sustain an adequate amount of IV fluids and electrolytes. To help the body to be nourished and prevent dehydration.   
• Surgery may be suggested. If invasive treatments do not decrease the size of the TM within two to three days, undergoing surgery is advised to remove part or whole of the colon.  

3. Would you know if you had toxic megacolon?

TM is a fatal life-threatening condition that can lead to inflammation throughout the body (sepsis), blood loss and potentially death.   

4. Can a colonoscopy detect megacolon?

During a colonoscopy, doctors are able to identify areas of damage and swelling of the colon. It will also determine the severity of TM. Doctors may also use a colonoscopy to determine the severity of how severe TM. As well as to monitor the condition and observe its treatment.