History and exam

Key diagnostic factors

common

presence of risk factors

It is important to elicit prior signs and symptoms that may suggest previous flares of inflammatory bowel disease, exposure to infectious agents, recent antibiotic use, and HIV/AIDS.

fevers/chills

Frequently present in toxic colitis and toxic megacolon (TC/TM).

tachycardia

Frequently present in TC/TM.

mental status changes

Frequently present in TC/TM.

hypotension

Frequently present in TC/TM.

abdominal distension

Toxic megacolon is characterised by either total or segmental colonic dilation >6 cm, which usually results in clinically evident abdominal distension though the degree of distension is variable.

Other diagnostic factors

common

diarrhoea

Prior bouts of diarrhoea, often lasting 1 week or longer, may be a presenting symptom if toxic megacolon is related to either ulcerative colitis (usually bloody diarrhoea) or infectious colitis. In some cases, improvement of diarrhoea heralds the onset of colonic dilation.

abdominal pain

Characterised as diffuse or focal crampy abdominal pain and may be relieved with bowel movements.

abdominal tenderness

The abdomen may be either focal or diffusely tender but the degree of pain may be masked by concurrent use of high-dose corticosteroid therapy. Localised and rebound tenderness may suggest impending perforation, while generalised peritonitis often indicates free perforation.

Risk factors

strong

ulcerative colitis (UC)

Although inflammatory bowel disease is the most common cause of toxic megacolon, the lifetime incidence in patients with UC is less than 5%.[4][5][8] In typical UC, inflammation and ulceration is limited to the mucosa; however, in toxic megacolon, inflammation extends into the smooth muscle layer, which may induce neural injury in the colonic wall, causing colonic paralysis and pronounced colonic dilation, thinning of the bowel wall, and deep ulcerations.[7][21][22]

In a study of patients requiring a colectomy for UC, a correlation between the depth of invasion and the degree of colonic dilation was demonstrated.[7][22] Toxic megacolon as a complication of an acute exacerbation of UC is an indication for urgent surgery.[5]

Crohn's colitis

The reported incidence of toxic megacolon complicating Crohn's colitis has great variability, ranging from 0% to 20% with a probable frequency of 2% to 4%.[4]

It has been suggested that toxic megacolon is more likely to occur early in the course of Crohn's colitis and that the fibrosing and segmental nature of Crohn's disease makes toxic megacolon less likely than with ulcerative colitis.

pseudomembranous colitis

Toxic megacolon has a reported lifetime incidence of 0.4% to 3% in patients with pseudomembranous colitis.[4] The incidence of toxic megacolon in patients with Clostridium difficile-associated colitis is increasing due to increasing prevalence of pseudomembranous colitis and other infectious colitides.[7]

Pathological hallmarks include diffuse ulcerations, raised mucosal nodules, yellowish-white superficial plaques interspersed between normal segments of mucosa, and extensive denudation seen on endoscopic inspection. However, stool testing has become a safer way to diagnose C difficile colitis than endoscopic evaluation of the acutely diseased and inflamed colon.

infectious colitis

Infectious agents including Clostridium difficile, Salmonella, Shigella, Campylobacter, Yersinia, Entamoeba histolytica, Cryptosporidium, and cytomegalovirus have been associated with colitis and toxic megacolon.[9][10][11][12][13][14][15][16]

HIV/AIDS/immunosuppression

Toxic megacolon has been reported as a consequence of cytomegalovirus infection in patients with HIV or AIDS.[14][15][16]

discontinuation of medications for inflammatory bowel disease

Discontinuation, or significant dosage decreases, of therapeutic medications including corticosteroids, sulfasalazine, or other aminosalicylates can trigger the development of toxic megacolon in patients with inflammatory bowel disease.[17]

antimotility agents

Drugs including narcotics, antidiarrhoeals, and anticholinergics, as well as some antidepressants, have been recognised to exacerbate colonic dilation and should be discontinued immediately if toxic megacolon is present.[7][17]

weak

chemotherapy/chemical immunosuppression

Antineoplastic agents and other associated immunosuppressants have been associated with toxic megacolon.[18][19][20]

electrolyte abnormalities

Several studies have noted electrolyte abnormalities in toxic colitis/toxic megacolon, especially hypokalaemia; however, whether this is a cause or an effect is debatable. Correction of electrolyte abnormalities, however, is a primary treatment objective.

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