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Understanding the Dexamethasone Suppression Test

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In this video we’re going to talk about the idea of cushions syndrome versus cushions disease and the idea behind the dexamethasone suppression test so the fundamental fundamentally we we have to understand that from the hypothalamus from the hypothalamus we get corticotrophic relation hormone that acts on the anterior pituitary and that and further produces

Adrenocorticotrophic hormone where from the adrenal cortex we get cortisol right so the dexamethasone suppression test you have a low dose so you have a low dose which is about one milligram so dexamethasone is a synthetic glucocorticoid so it is very similar in nature to cortisol so it’s about one milligram for the low dose test and what you’re really testing

For with a low dose is cushing’s syndrome so what happens is that when i give a synthetic glucocorticoid like dexamethasone one milligram it should simulate cortisol to go ahead to the anterior pituitary and the hypothalamus to negative feedback right so as a result i should have my crh to decrease eventually from the anterior pituitary i should have a decrease

In acth and as a result eventually my cortisol level should decrease so in a normal patient when i give a low dose of one milligram dexamethasone the the cortisol levels should decrease now let’s say you have cushion syndrome and then there’s something from the adrenal cortex that’s causing the problem right so this loads amount of cortisol what would happen

What do you expect to happen in the dexamethasone suppression low-dose one milligram test well because your body is so used to producing this large amount of cortisol one milligram which is very small it’s not enough to cause a negative feedback effect on your hypothalamus as well as your anterior pituitary to produce uh lower amounts of acth that eventually

Would decrease the cortisol levels it’s just not enough and so as a result with the low dose dexamethasone suppression test of one milligram a positive test for cushing’s syndrome right a positive test cushion syndrome would be an increase in cortisol levels so the cortisol levels will not decrease so it’s just not enough to decrease the cortisol levels so below

Those next methods on suppression test cortisol levels are still high right so high cortisol levels or cortisol levels in low dose is a positive test now let’s talk about another scenario where there could be a pituitary adenoma and this is when we talk about the high dose eight milligrams right so if you give a high dose eight milligrams of pituitary adenomas

So again it’s usually given at night around 11 pm and then the patient comes in the morning at 8 a.m to get the levels measured so let’s say you give this patient a high dose of 8 milligram dexamethasone so it’s going to uh mimic cortisol again go up to the anterior pituitary and the hypothalamus and it’s going to decrease your crh decrease secretion from the

Anterior perturbator and as a result your ac th is going to decrease and your cortisol is going to decrease so with cushin’s disease right so with cushing’s disease it’s usually a pituitary adenoma so right so pituitary right dexamethasone this eight milligram it’s so strong and so high that even though there’s a pituitary adenoma it’s still enough to decrease

Your acth release and as a result the cortisol levels will decrease right so that is a response for cushing’s disease with the eight milligram dexamethasone um with the eight milligram dexamethasone suppression test so let’s look at another scenario where you might have an adrenal adenoma right from the adrenal cortex and what the response would be from the eight

Milligram dexamethasone suppression test right so i’m gonna give eight milligrams of dexamethasone again it’s gonna travel up to the anterior protector and the hypothalamus as a result from the negative feedback i should get decreased crh and decrease ac so my ac th should decrease as well but because the pituitary because the adenoma is right here the eight

Milligram dexamethasone will have no effect on the adrenal cortex and so as a result the cortisol levels will still remain high so with response with responding to an eight milligram dexamethasone suppression test for in fact cushion syndrome the cortisol levels are going are going to remain high right but you’re going to have low acth right when we talk about

Cushing’s disease of pituitary adenoma like we said earlier the dexamethasone is enough to suppress the release of acth from the anterior pituitary even though there’s an adenoma there and that’s the basis behind the dexamethasone suppression test

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Understanding the Dexamethasone Suppression Test By Kevan Science