Introduction
Background
Toxic megacolon is defined as a severe episode of colitis with segmental or total dilatation of the colon. It is typically a complication of ulcerative colitis, but it may be a complication of Crohn disease, antibiotic-related pseudomembranous colitis, and other colitides. Pathologically, acute fulminant colitis is associated with neuromuscular degeneration and a rapid and extensive colonic dilatation.
The diagnosis of toxic megacolon is based on clinical findings, simple laboratory results, and a careful scrutiny of the plain abdominal radiograph. Usually, no other radiologic investigations are required. Once toxic megacolon is diagnosed, the patient must be immediately admitted to an intensive care unit where he or she can be monitored by intensivists and a team of physicians and surgeons. The mortality rate is high, at 20%.
Double-contrast barium enema studies in a 44-year-old man known to have long history of ulcerative colitis. Images show total colitis and extensive pseudopolyposis (see also Image 2 in Multimedia).
A 22-year-old man presented with abdominal pain, passage of blood and mucus per rectum, abdominal distention, fever, and disorientation. Findings from sigmoidoscopy confirmed ulcerative colitis. Abdominal radiographs obtained 2 days apart show mucosal edema and worsening of the distention in the transverse colon. The patient's clinical condition deteriorated over the next 36 hours despite steroid and antibiotic therapy, and the patient had to undergo a total colectomy and ileostomy.
Pathophysiology
Megacolon may occur acutely or as a chronic illness.1 Acute megacolon that occurs in association with severe inflammation of the colon is known as toxic megacolon, whereas acute megacolon without obvious colonic disease is known as Ogilvie's syndrome.
Toxic megacolon is often seen in the setting of ulcerative colitis.2 If severe enough, many other colitides can precipitate a toxic megacolon. Crohn disease, antibiotic-induced pseudomembranous colitis, amebiasis, Salmonella enteritis and Campylobacter enteritis infection (particularly when antimotility agents are used), and ischemic colitis are all known causes of toxic megacolon.3,4,5
Methotrexate, vincristine, and high-dose therapy with autologous stem-cell transplantation for amyloidosis-induced toxic megacolon have also been reported.6 The colon is a frequent site of gastrointestinal complications in patients with HIV infection; these colonic disorders increase in frequency as the immunodeficiency worsens. The most common manifestations of colonic disease in AIDS are diarrhea, lower gastrointestinal bleeding, and abdominal pain; however, toxic megacolon has also been reported.
Toxic megacolon almost always occurs in the setting of pancolitis, although the rectum may be spared. Megacolon is considered to be present if the diameter of the colon is 5.5 cm or more, with apparent edema of the bowel wall on plain abdominal radiographs. Rarely, the toxic dilatation may extend to the terminal ileum. Colonic dilatation may be superimposed on an acute fulminant colitis in a patient with a history of inflammatory bowel disease. The dilatation may fluctuate or resolve completely, leaving the patient with toxic colitis. Clostridium difficile is the most common causative agent implicated in pseudomembranous colitis.7,8,9
Toxic megacolon secondary to infective colitis is rare in children, but when it occurs, it may be fulminating and potentially fatal. The mortality rate is 15%, and 15% of children require surgery.
The course of the disease can be divided into 3 stages: the acute toxic stage, the gut-failure stage, and the convalescence or deterioration stage. Bacterial and/or endotoxin translocation is believed to play an important role in gut failure.
Toxic megacolon is associated with an acute transmural fulminant colitis with the neurogenic loss of motor tone. The result is the rapid development of colonic dilatation resulting from damage to the entire wall of the colon associated with neuromuscular degeneration. Histologic examination reveals extensive sloughing of the mucosa and frequent necrosis of the muscle layers of the bowel wall. Thinning of the muscle layer of the colon often occurs.
Frequency
United States
To the author's knowledge, no reliable demographic data describe the incidence of toxic megacolon as a complication of ulcerative colitis and other colitides.
International
To the author's knowledge, no data suggest that the worldwide incidence or prevalence of toxic megacolon differs from that in the United States.
Mortality/Morbidity
Toxic megacolon is a fulminating and potentially lethal complication of severe colitis. The disease requires intensive treatment and has a prolonged convalescence period. The mortality rate is 20% in adults and 15% in children.
Race
No racial predilection is noted.
Sex
No sex preponderance is reported.
Age
Most cases affect young adults, but individuals of any age can be affected. Toxic megacolon secondary to infective colitis is rare in children, but when it occurs, it may be fulminating and potentially fatal.
Presentation
Toxic megacolon is a clinical diagnosis, one based on thorough history taking and physical examination and supported by plain abdominal radiographic findings. Patients have abdominal distention, pain, diarrhea, fever, and dehydration; some patients progress to shock.10 The symptoms may ensue in the setting of known inflammatory bowel disease or antibiotic therapy. In patients receiving steroids, some of the clinical features may be masked. Clinical examination is not accurate in the detection of perforation in the setting of toxic megacolon. The first hint of a colonic perforation may be provided on a plain abdominal radiograph.11,12,13,14
Preferred Examination
Patients with toxic megacolon often present in the emergency department as having abdominal distention superimposed on chronic or acute diarrhea. The diagnosis should be considered in all such patients. The diagnosis is usually based on thorough clinical history taking and physical examination combined with plain abdominal radiography. CT has a limited role, although it better depicts the anatomic detail of transmural disease, mesenteric involvement, and intraperitoneal complications of inflammatory bowel disease.15 Ultrasonography and radionuclide studies have a limited role if any.16,17,18,19
Limitations of Techniques
Chagas disease, Hirschsprung disease, and intestinal pseudo-obstruction may superficially resemble toxic megacolon on plain radiographs.20,21 However, because they occur in totally different clinical settings, they are unlikely to be confused with toxic megacolon.
Differential Diagnoses
Colitis, Ischemic
Colitis, Pseudomembranous
Crohn Disease
Hirschsprung Disease
Ulcerative Colitis
Other Problems to Be Considered
Chagas disease
Bowel pseudo-obstruction
More on Toxic Megacolon |
 Overview: Toxic Megacolon |
| Imaging: Toxic Megacolon |
| Follow-up: Toxic Megacolon |
| Multimedia: Toxic Megacolon |
| References |
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References
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Further Reading
Keywords
severe colitis, segmental dilatation of the colon, total dilatation of the colon, ulcerative colitis, pancolitis, acute transmural fulminant colitis, Crohn disease, Crohn's disease, antibiotic-induced pseudomembranous colitis, amebiasis, Salmonella enteritis, S enteritis, Campylobacter enteritis, C enteritis, ischemic colitis
