Toxic Megacolon

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DEFINITION

Life-threatening condition involving gross dilation of the colon with systemic manifestations and risk of perforation.

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EPIDEMIOLOGY

As per cause
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AETIOLOGY

Pathogenesis
Rapid dilation of the proximal colon.
Typically with a thickened severely inflamed distal colon.

Inflammatory
UC (most often but decreasing)
Crohn's

Infective

Bacterial
C diff (increasing with strain virulence & resistance)
[all the rest are rare:]
Salmonella
Shigella
Campylobacter
Yersinia

Parasitic
E. histolytica
Crytposporidium

Viral
CMV colitis

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BIOLOGICAL BEHAVIOUR

Pathophysiology

Combination of severe inflammation and local mediator release.
Damage extends into SM --> paralysis and dilation
Bacterial translocation leads to bacteraemia and systemic toxicity
NO from inflamed SMCs may also promote dysmotility and dilation

TM is a misnomer: the toxic segment is not the dilated segment.
And in many toxic patients, there is minimal dilation.

Natural history
IBD patients will commonly develop colonic dilation
1/3 within 3 months, 2/3 within 3 years
May turn toxic after repeat recent attacks of colitis, change of serious medications, HIV, barium enema.

Complications
Systemic sepsis
Perforation
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MANIFESTATIONS

Symptoms
Local
Abdominal distension
Diarrhoea; possibly bloody
Systemic
Toxic; SIRS
- fever typically >38.6 and HR>120 in significant toxicity
- WCC >10

Signs
Abdo distention
Often very tender

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INVESTIGATIONS

Imaging
Colonic dilation
Ascending / transverse >6
- up to 15cm
- absolute size less important than rate of distention, if known
Concurrent small bowel dilation is a bad sign in UC.
Thickening and edema of the transverse and left colon.

Bloods
Anaemia, leukocytosis
Electrolyte imbalance
Hypoalbuminaemia is a poor prognostic sign.

Micro
Stool cultures for MCS and c.diff toxin assay
Blood cultures

Endoscopy
Barium enema and colonoscopy can result in deadly perforation.
Limited colonoscopy if any; not a complete colonoscopy
- biopsies may help in confirming underlying cause if not already known

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MANAGEMENT

Principles
Multidisciplinary; early surgical involvement
Clear criteria for continuing medical management vs surgical intervention from outset
ICU review and care.

Medical

1. Eliminate exacerbating factors
- electrolyte imbalance
- anti-motility agents, opiates, anti-cholinergics, antidepressants

2. Bowel rest, NG tube

3. Prophylaxis
- PPIs
- DVTs

4. Close Review
- blds, serial XRs every 12h until improving.

5. IBD Therapy
- high-dose steroids, eg hydrocort 100mg q8h

6. C-Diff Therapy
- antibiotics as per notes
- early surgical intervention saves lives

Operative

Medican management above can be effective in 50-75%
But be vigilant and operate quickly when indicated

Indications
Free perforation
massive haemorrhage
Progression of colonic dilation
Failure to improve in 48h (relative indication)
- mortality much better if perf prevented; 10% vs 40%
Ongoing major concern after 7 days (relative)

Procedure
Open subtotal colectomy and end ileostomy
Beware fragile bowel; high risk of intra-operative perf
Divide rectum as low as possible to minimize blow-out and leave a large rectal tube (5d at least).

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REFERENCES

Cameron 10th

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