Pheochromocytoma

[Phloston]

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Could someone please give the mechanism for why orthostatic hypotension occurs with pheochromocytoma?

Does it have to do with decreased responsiveness to compensatory SNS-induced vasoconstriction upon standing because the pt is already somewhat desensitized from having heaps of catecholamines floating around?

Cheers,

 

[ohyeahbaby]

Could someone please give the mechanism for why orthostatic hypotension occurs with pheochromocytoma?

Does it have to do with decreased responsiveness to compensatory SNS-induced vasoconstriction upon standing because the pt is already somewhat desensitized from having heaps of catecholamines floating around?

Cheers,

that's what I've always thought, i.e. that A1 was desensitized

 

[usmlesuccess]

Are you sure that pheochromocytoma causes orthostatic hypotension? I remember that orthostatic hypotension is a side effect of treatment with phenoxybenzamine after excision of pheochromocytoma, but I never heard that ortho stat hypo is a symptom of the actual disease. I am sure that I must have missed something.

 

[Phloston]

Are you sure that pheochromocytoma causes orthostatic hypotension? I remember that orthostatic hypotension is a side effect of treatment with phenoxybenzamine after excision of pheochromocytoma, but I never heard that ortho stat hypo is a symptom of the actual disease. I am sure that I must have missed something.

I just encountered an easy question in GT, but had noticed that the woman had something like 165/100 lying down and 110/85 standing, and then the explanation said that the orthostatic hypotension further supported the already obvious PCO. However, OH wasn't obvious to me.

 

[ohyeahbaby]

Are you sure that pheochromocytoma causes orthostatic hypotension? I remember that orthostatic hypotension is a side effect of treatment with phenoxybenzamine after excision of pheochromocytoma, but I never heard that ortho stat hypo is a symptom of the actual disease. I am sure that I must have missed something.

I am 100% sure pheochromocytomas causes orthostatic hypotension. I just forget where I know that from. Either Uworld or usmleRX.

 

[OveractiveBrain]

Could someone please give the mechanism for why orthostatic hypotension occurs with pheochromocytoma?

Does it have to do with decreased responsiveness to compensatory SNS-induced vasoconstriction upon standing because the pt is already somewhat desensitized from having heaps of catecholamines floating around?

Cheers,

Thats not in the usualy presentation of pheo. Its some bullshit theoretical mechanism they are testing you about. And, if its true, its only in the variant that is "always on" which pheo usually isnt. Don't know where this is coming from, and sounds like a "in order to get a 280, memorize this fact." Straight up, i wouldn't learn it.

After answering three of your questions, gunner training questions sound bogus. Just saying.

 

[AndyRSC]

gunner training questions sound bogus

👍

There is, however, some research on this. Most likely mechanism is simply the reduced responsiveness of vasculature to NE, namely the veins in which blood pools orthostatically, which likely occurs due to down-regulation of alpha1 receptors due to persistent elevation of NE.

 

[Chirurg]

Could someone please give the mechanism for why orthostatic hypotension occurs with pheochromocytoma?

Does it have to do with decreased responsiveness to compensatory SNS-induced vasoconstriction upon standing because the pt is already somewhat desensitized from having heaps of catecholamines floating around?

Cheers,

My understanding is decreased intravascular volume causes OH in Pheo.
look into that. but as some one pointed out, nothing is clear cut in Pheo and OH in Pheo just serves to highlight a physiological principle. I will look into this again if I have more time.

 

[Phloston]

My understanding is decreased intravascular volume causes OH in Pheo.
look into that. but as some one pointed out, nothing is clear cut in Pheo and OH in Pheo just serves to highlight a physiological principle. I will look into this again if I have more time.

Brilliant. I just searched online and that's exactly it. Numerous sources say the orthostatic hypotension is due to volume depletion. Thanks for mentioning that.

Of course none of them say a mechanism, which I would guess would just be that aldosterone and vasopressin are generally secreted less substantially in order to compensate for the catecholamine-induced vasoconstriction.

 

[mpatricksweeney]

To complicate further...I just had a UWorld question on MEN2A. Patient with high u[VMA], adrenal mass and orthostatic HYPERtension (200/120 standing, 190/110 seated). There are articles describing ortho hypo- and hypertension associated with phaeo. Sounds like variable presentation, but which of the orthostatic pathologies is classic in phaeo? (Outside phaeo, orthostatic hypertension often due to adrenergic hypersensitivity. If there's adrenergic desensitization in phaeo, hypertension seems unlikely. But UWorld don't make mistakes...)