Differentials
Acute colonic pseudo-obstruction
SIGNS / SYMPTOMS
Impressive abdominal distension yet little or no abdominal tenderness.
Several conditions are associated with the development of colonic pseudo-obstruction. These include chest infection, myocardial infarction, renal failure, and Parkinson’s disease. Colonic pseudo-obstruction is also associated with trauma, recent major orthopaedic surgery such as hip replacement, the use of neuroleptics or opiates, and metabolic disturbances.[1][24]
INVESTIGATIONS
CT or contrast enema confirms diagnosis and excludes mechanical causes.
Chronic/idiopathic megacolon
SIGNS / SYMPTOMS
Long-standing history of constipation, diarrhoea, or incontinence.
Visceral neuropathy. May also be part of an acquired visceral neuropathy (e.g., Chagas' disease).
Drug history may include risperidone.
Preceding viral infection.
Recurrence after resection implies a misdiagnosed megacolon.
INVESTIGATIONS
Difficult to differentiate; can be radiologically similar to sigmoid volvulus and respond rapidly to rectal tube decompression.
Colonic transit studies and anorectal manometry assist in this difficult diagnosis. A slow colonic transit may be identified. Anorectal physiology excludes Hirschsprung's disease where a normal recto-anal inhibitory reflex is identified.
Toxic megacolon
SIGNS / SYMPTOMS
Presence of an initial colitis of any cause.
Signs of sepsis (e.g., fever, tachycardia, hypotension, poor capillary refill) in early stages.
INVESTIGATIONS
Diagnosis may be apparent from clinical picture.
Plain abdominal x-ray may show "thumb printing" or intraluminal soft tissue mass (pseudopolyps).
Cautious colonoscopy confirms the diagnosis not only by the typical mucosal appearance, but also by biopsy.
Colonoscopy should be with minimal insufflation and rarely proceeds beyond the rectum and sigmoid once colitis is confirmed endoscopically, owing to the risk of perforation.
Pseudomembranous colitis
SIGNS / SYMPTOMS
Recent history of antibiotic or immunosuppressant use.
Profuse, foul-smelling diarrhoea.
INVESTIGATIONS
Elevated WBC count.
Colonoscopy may identify pseudomembranes and exclude mechanical obstruction.
Stool culture isolates Clostridium difficile.
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