Toxic megacolon is a potentially lethal complication of inflammatory bowel disease (IBD) or infectious colitis that is characterized by total or segmental nonobstructive colonic dilatation plus systemic toxicity [1-3]. Colonic dilatation is also observed in patients with congenital megacolon (Hirschsprung's disease), idiopathic or acquired megacolon occurring with chronic constipation of any etiology, and intestinal pseudoobstruction, a manifestation of diffuse gastrointestinal dysmotility of various causes. However, the lack of systemic toxicity distinguishes these presentations from true toxic megacolon. (See "Acute colonic pseudo-obstruction (Ogilvie's syndrome)".)
The precise incidence of toxic megacolon is unknown. The incidence in ulcerative colitis and Crohn's disease was approximately 1 to 5 percent two decades ago , but has gradually decreased because of earlier recognition and intensive management of severe colitis. Clinically symptomatic Clostridium difficile infection occurs in approximately 1 percent of all hospitalized patients; a few of these may develop severe colitis with toxic megacolon [5-7]. (See "Clostridium difficile in adults: Clinical manifestations and diagnosis".)
Although most commonly recognized as a complication of IBD, toxic megacolon may also occur with infectious colitides of diverse etiology, ischemic colitis, volvulus, diverticulitis, and obstructive colon cancer (table 1).
- Clinical features that suggest IBD as a cause of toxic megacolon include a preceding history of diarrhea, bloody stools, abdominal pain, perianal disease, or extraintestinal manifestations such as arthritis, iritis, skin disease, or liver disease. (See "Clinical manifestations, diagnosis, and prognosis of ulcerative colitis in adults" and "Clinical manifestations, diagnosis and prognosis of Crohn disease in adults".)
- Risk factors for the development of severe colitis in patients with C. difficile infection include malignancy, chronic obstructive pulmonary disease, immunosuppressive therapy, renal failure, or exposure to antiperistaltic medications or clindamycin . Toxic megacolon has been described in patients with recurrent C. difficile .
- Salmonella, Shigella, and Campylobacter colitis are very rarely complicated by toxic dilatation, and can usually be differentiated from IBD by histology and endoscopic biopsy . Toxic megacolon may also complicate hemorrhagic colitis and hemolytic-uremic syndrome secondary to infection with E. coli O157 .
- Fewer than 3 percent of patients with amoebic colitis have a fulminant clinical course, and a small fraction develop toxic megacolon. The use of loperamide in amoebic colitis may precipitate toxic megacolon .
- In patients with HIV infection or AIDS, cytomegalovirus (CMV) colitis is the leading cause of toxic megacolon and emergency laparotomy; this usually occurs in the setting of disseminated CMV infection. CMV infection of the colon may also precipitate toxic megacolon in patients with IBD . In one series, for example, 6 of 46 resected colons in patients with ulcerative colitis showed evidence of CMV infection; 5 of these 6 patients had toxic dilatation compared with only 2 of the remaining 40 patients without CMV infection .
A number of pathogenic mechanisms probably contribute to the development of toxic megacolon in patients with IBD . One possible mechanism is that mucosal inflammation leads sequentially to the release of inflammatory mediators and bacterial products, increased inducible nitric oxide synthase, generation of excessive nitric oxide, and colonic dilatation.