January 26, 2023

#drk #medical #learnmedical #basic #medico #hexamethasone #suppression #test #diagnosis #test #basicmedicalcontent

Hi this is tom from zero2finals.com i wanted to go through the dexamethasone suppression test before we go through this test a prerequisite is to understand the adrenal axis and understand the causes of cushing syndrome now in order to do that you can go and check out the video that i made that should explain everything that you need to know to get into this video

So to start with why do we do the dexamethasone suppression test the idea is to confirm a diagnosis of cushing’s syndrome an excessive cortisol and then secondly to understand what the cause of that cushing syndrome is where that what what the source of that excessive cortisol is so how is the test done well you give dexamethasone at 10 pm at night and the next

Morning you measure their cortisol and their acth so it’s really done in two stages the first stage is the low dose test where one milligrams of dexamethasone is used this test is really to confirm whether the patient’s got a normal response and they have a normal adrenal axis or to confirm that they actually have cushing syndrome the second step is the high-dose

Test where we use eight milligrams of dexamethasone and this is really to look at what the cause of that excessive cortisol or cushing syndrome is okay so let’s move on to understanding how the test works so firstly let’s look at the low-dose test with one milligrams of dexamethasone so in a normal situation this one milligrams of dexamethasone which is an

Exogenous steroid which acts very similar way to cortisol will act on the hypothalamus to suppress crh it’ll act on the pituitary to suppress acth which in turn will cause a reduction in cortisol so a normal response to one milligram low-dose dexamethasone suppression test is a reduction in cortisol now what happens if you have and then if you have a high level

Of cortisol to begin with really meaning that you have a cushings syndrome well uh this cushing syndrome is already so high that this measly one milligram of dexamethasone is not enough to cause any suppression if your body’s used to having loads of cortisol adding another one milligrams of dexamethasone won’t make too much difference so a positive result from

The low dose dexamethasone suppression test is that could saw remains high or really within the normal range and this is suggestive of a cushing syndrome okay so now let’s look at if you have a positive low-dose text message zone suppression test you go on to do a high dose test with eight milligrams of dexamethasone so now let’s look at the scenarios let’s say

You have cushing’s disease right where you have an ex where you have a pituitary adenoma that’s producing acth that’s acting on the adrenal gland to produce loads of cortisol and that’s that cushing’s disease is the cause of your high cortisol now this big dose of dexamethasone is enough to cause a suppression of the anterior pituitary even though there’s an

Adenoma there so what you find if you have a high-dose x methylone suppression test and cushing’s disease is that it’s enough to reduce the acth and in turn reduce the cortisol so this is what you have uh in a pituitary adenoma as a result of the as a response to the test so now let’s look at the scenario where you have an adrenal gland tumor and it’s this tumor

Or this adrenal adenoma that’s producing loads of cortisol now this big dose of dexamethasone will head up to the hypothalamus and reduce crh it’ll head over to the pituitary and block acth but it has no effect on the adrenal gland so you still get this large amount of cortisol being pumped out so the result in an adrenal tumor from the dexamethasone suppression

Test is that you have high cortisol and a low act h okay so now let’s look at the final scenario where you have a lung cancer or some other neoplasm that’s pumping out ectopic acth right so you give them the dexamethasone it heads over to the hypothalamus and reduces the crh it heads over to the pituitary and this stops producing acth but you still have loads

Of acth in your system because it’s being produced from somewhere else it’s being produced from this cancer in the lungs as a result it continues to stimulate the adrenal gland and you continue to have a high cortisol so in a perineal plastic cushings uh uh a high-dose dexamethasone test will lead to a raised acth and a raised cortisol so let’s look at a sort

Of summary of that so in a low-dose test if you have low cortisol afterwards that’s means you have a normal adrenal axis and no cushings if you have a high or normal cortisol afterwards that suggests you have cushing syndrome now you go on to have a high dose test if you have a low cortisol after the high-dose test that’s diagnostic of cushing’s disease which

Remember is a pituitary adenoma and the eight milligrams is enough dexamethasone to suppress that adenoma leading to a reduction in cortisol now uh if you have a high or normal cortisol after a high dose of dexamethasone but your acth is low this suggests an adrenal cushings so there’s an adrenal tumor that’s pumping out the acth that’s pumping out the cortisol

Acth is still suppressed but cortisol remains high or normal now let’s say you have a higher normal cortisol and the acth is high this is because the acth is coming from somewhere other than the pituitary gland i.e a small cell lung cancer so you end up with a highest th and a resulting high cortisol so i hope that’s cleared up some of the confusion about the dex

Methanone suppression test and you now understand how to interpret all of the results if you like this video like or comment or subscribe on the youtube channel head over to xerotofinos.com for more resources and i’ll see you next time

Transcribed from video
Dexamethasone suppression test | Diagnosis Test By Basic Medical Content