Toxic Megacolon

Toxic megacolon is one of the most life-threatening complications of severe ulcerative colitis. The terms of toxic colitis and toxic megacolon are often interchangeably but not correctly used. Whereas toxic colitis implies an acutely ill patient with a diseased colon, toxic megacolon is defined as total or segmen-

tal [6] nonobstructive hypotonic dilatation of the colon exceeding 6 cm in diameter in the transverse colon on plain abdominal film, with or without signs of systemic toxicity [7-10]. An overall incidence of about 8% of toxic megacolon in ulcerative colitis patients' admission is generally observed [11]. Small bowel distension may precede colonic dilatation and is reported as impending megacolon. This condition is present in about 50% of patients affected by severe ulcerative colitis and is at high risk for development of toxic megacolon. Both conditions, impeding megacolon and toxic megacolon, may be associated with development of multiple organ dysfunction syndrome (MODS), which is responsible of high mortality rates. Remarkably, mortality is similar in patients with pancolitis or with limited colitis but is significantly higher in perforated patients [12, 13]. Although an increasing number of patients is now successfully managed with medical treatment, up to 50% will require urgent or emergent colectomy [14].

The exact explanation for toxic megacolon is not known; the pathogenic mechanism driven by soluble inflammatory mediators and bacterial products, leading to downstream inhibitory effect on colonic muscle tone, could be one of the key players responsible for the and systemic inflammatory response syndrome [11, 15]. Appearance of gastrointestinal distension during the clinical course of acute ulcera-tive colitis attack should be considered an alarm signal for toxic megacolon or systemic multiorgan dysfunction leading, with high probability, to an emergent colectomy. A certain number of patients presents with toxic megacolon during the first bout of ulcerative colitis or within 2-3 months of diagnosis. Mean duration of disease, before the attack, has been reported to be 3-5 years [6,16]. Many patients present in the midst of an ongoing attack of severe colitis, with a predominating clinical picture before the onset of toxic megacolon. Patients are acutely ill, with fever, chills and abdominal cramping. Toxic megacolon may be heralded by tachycardia, leukocytosis, dehydration, bloody diarrhoea, abdominal distension, pain and tenderness. Jalan's clinical criteria for diagnosis of toxic megacolon are fever >38.6°C, heart rate >120 beats/min, white blood cell count >10.500/ mm3 and anaemia, plus one of the following criteria: dehydration, mental changes, electrolyte imbalance or hypotension [16]. Radiological findings show dilatation of transverse or ascending colon >6 cm in patients in the supine position [8], small bowel dilatation with gas shadow areas greater than 36.5 cm2 and gastric distension with disappearance of gastric mucosal folds. Computed tomography (CT) and magnetic resonance imaging (MRI) scan findings are colonic dilatation >6 cm, abnormal haustral pattern, diffuse colonic wall thickening, submucosal oedema, pericolic stranding, ascites, perforations and adjacent abscess and ascending pyelophlebitis with septic emboli. Delaying treatment increases the risk of perforation, which raises mortality from less than 5% to nearly 30% [2, 5].

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