Carcinoid Syndrome

sillymoo

Ok, the answer to this is probably staring at me somewhere but in my feverish, pre-exam state, I just cant seem to get my head around it.

Carcinoid syndrome develops secondary to carcinoid tumours, this I get. The symptoms develop when the serotonin produced by the tumour escapes hepatic detoxification. So where does the tumour have to be for this syndrome to develop? In my notes most carcinoid tumours occur along the ileum, appendix, bronchus. If so how does the serotonin avoid being detoxified, be it in the liver or in the lung????

Is it that the bronchial veins carry serotonin from the tumour and thus is not inactivated in the lung??

My head is sore

DrIndy

Carcinoid syndrome is an interesting disease - it follows a rule of thirds 1/3 multiple, 1/3 metastasise, 1/3 are in the GI tract, 1/3 are multiple etc....

Although the liver breaks down serotonin, if they arise outside of the GI tract, then they have a systemic effect because the portal circulation and breakdown is bypassed, likewise if a GI carcinoid has metastatic deposits - either in the liver or beyond, it has bypassed the portal circulation and hence has malignant carcinoid.

The bronchial carcinoids cause malignant carcinoid. Liver carcinoid has bypassed the portal circulation and cause malignant carcinoid.

GI or appendix carcinoid is still confined to the gut - hence the liver prevents systemic or malignant carcinoid.

Here's more info:

http://emedicine.medscape.com/article/282515-overview

hope this helps!

charlieroot

From memory if you are you symptomatic from a carcinoid tumour (primary or secondary) there are 2 possibilites:
1) The portal venous system is bypassed ie - the tumour is draining to systemic venous system.
2) The liver has a limited capacity to metabolise serotonin - once the tumour is producing serotonin in excess of this you become symptomatic.

Lastly, interesting point - the lungs also metabolise serotonin which is why in long term carcinoid syndrome you get right sided heart pathology but not left sided !

sillymoo

charlieroot wrote: »

Lastly, interesting point - the lungs also metabolise serotonin which is why in long term carcinoid syndrome you get right sided heart pathology but not left sided !

Thanks for the help Indy and Charlie. I did not realise they can occur anywhere, but most commonly in GIT and bronchus. Also I now understand why it causes pulmonary valve stenosis and not mitral valve stenosis :cool:

Cheers