toxic megacolon in UC

[Suncrusher]

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Why doesn't it happen more often in Crohns as well? Crohns is the IBD that has transmural inflammation and seems intuitively more likely than UC to cause paralytic ileus of the muscularis externa, but all the step1 review sources seem to say that UC is the IBD most associated with toxic megacolon, and the second most common inflammatory cause is pseudomembranous colitis, although it can rarely happen in Crohns. I'm confused.

 

[MLT2MT2DO]

Why doesn't it happen more often in Crohns as well? Crohns is the IBD that has transmural inflammation and seems intuitively more likely than UC to cause paralytic ileus of the muscularis externa, but all the step1 review sources seem to say that UC is the IBD most associated with toxic megacolon, and the second most common inflammatory cause is pseudomembranous colitis, although it can rarely happen in Crohns. I'm confused.

I could probably go into more detail, but I won't. It pretty much can be simplified as UC=Large Intestine (toxic Megacolon is an issue with the large instestine as I'm sure you know) vs Crohns=Anywhere in GI. With that said I'm sure it can happen in Crohn's. Also I'd be surprised if Pholston doesn't have a take on this

 

[dragon529]

Pholston is currently busy sitting the exam right now!!!

 

[Suncrusher]

I could probably go into more detail, but I won't. It pretty much can be simplified as UC=Large Intestine (toxic Megacolon is an issue with the large instestine as I'm sure you know) vs Crohns=Anywhere in GI. With that said I'm sure it can happen in Crohn's. Also I'd be surprised if Pholston doesn't have a take on this

Makes sense; I'll go with that for now. Thanks

 

[gravitywave]

law of laplace. wall tension increases with radius. colon has a bigger radius than small bowel, therefore it is more prone to dilation and rupture.

 

[ijn]

Why doesn't it happen more often in Crohns as well? Crohns is the IBD that has transmural inflammation and seems intuitively more likely than UC to cause paralytic ileus of the muscularis externa, but all the step1 review sources seem to say that UC is the IBD most associated with toxic megacolon, and the second most common inflammatory cause is pseudomembranous colitis, although it can rarely happen in Crohns. I'm confused.

My guess is it all comes down to real estate. For example both Crohns and UC can cause colon cancer, but classically UC is more so associated with colon cancer because it involves a larger area of the colon. If you had pan-colonic Crohn's you'd probably be at just a high of risk of cancer or toxic megacolon as pan-colonic UC.

10% of UC admissions have toxic megacolon, while 2.3% of Crohn's admissions have toxic megacolon. Less common for sure, but I wouldn't say it's rare.