Hey guys! In this video, I have explained the dexamethasone suppression test It is used to diagnose different types of Cushing Syndrome
Hey everyone welcome back in this video i’m gonna be explaining the dexamethasone suppression test we’re gonna learn this topic by solving questions so that you understand it better dexamethasone is basically a corticosteroid it can be used to diagnose cushing’s syndrome this can be done at two levels a low dose dexamethasone test and a high-dose dexamethasone
Test under normal circumstances the hypothalamus produces corticotropin releasing hormone this triggers the pituitary to release adrenocorticotropic hormone acdh ultimately goes to the adrenals and stimulates it to secrete cortisol cushing’s syndrome is a condition in which there is a lot of cortisol in the blood this could either be due to an excessive cortisol
Production by the adrenals consumption of exogenous steroids excessive acth production by the pituitary or due to ectopic acth production as seen in some malignancies the dexamethasone suppression test will help us find the most likely cause let’s see how question number one low ac th high cortisol after an overnight low dose dexamethasone suppression test is
Likely to be due to option a exogenous administration of steroids option beam cushioning disease option c ectopic acth production option d this is a normal finding let’s first understand the low dose dexamethasone suppression test what happens here is that the patient is given one milligram of dexamethasone at night the next morning the cortisol levels are checked
Dexamethasone is a corticosteroid so it will inhibit acth and crh by negative feedback since there’s less stimulation coming from above the adrenals will secrete less cortisol ultimately when cortisol levels are checked in the morning they will be reduced however in patients with cushing’s syndrome the cortisol levels will remain high despite the negative feedback
In order to differentiate these conditions we go ahead to check the acdh levels in patients with an adrenal adenoma there will be high cortisol produced autonomously by the adrenals this cortisol suppresses the acth by negative feedback hence the acth levels will be low in such cases similarly in patients taking exogenous steroids the negative feedback by these
Drugs will reduce the levels of acth ultimately acdh levels will be low in these two cases we can differentiate one from another by reviewing the patient’s medical history and by performing a ct to identify the adenoma these two conditions are independent of acph so the correct answer is exogenous administration of steroids normal findings would have low cortisol
Levels cushing disease and ectopic acth productions will have high acth and high cortisol after an overnight low dose dexamethasone suppression test cushing’s syndrome can also be caused due to an issue at the level of the pituitary this is typically going to be a pituitary adenoma that makes a lot of acth this is called cushing disease this acdh8 stimulates
The adrenals resulting in a lot of cortisol this acth is produced by an adenoma so low dose dexamethasone does not suppress it hence in such cases both acth and cortisol levels will be high despite the negative feedback exerted by lodo’s dexamethasone similarly in patients with ectopic acth production acth is made and places apart from the pituitary this is
Typically seen in patients with lung cancer since acth is not produced in the pituitary negative feedback will not work here so these patients will have high acth and high cortisol after an overnight low dose of dexamethasone in order to differentiate these two conditions we perform the high-dose dexamethasone suppression test question number two low acth low
Cortisol after a high-dose dexamethasone suppression test is likely to be due to option a pituitary adenoma option b lung cancer in this test 8mg of dexamethasone is given high dose dexamethasone is able to suppress the acth produced by the pituitary adenoma so the results in such case would be low cortisol and low acdh however high dose dexamethasone does not
Suppress the acth produced by lung cancer so the results here would be high acth and high cortisol here’s how i think of it since the pituitary adenoma is benign it can be suppressed by high dose dexamethasone however since lung cancer is malignant it cannot be suppressed we can locate the adenoma with an mri of the brain ectopic acth production can be located
By performing a ct of the chest abdomen and pelvis so the correct answer is pituitary adenoma known as cushing disease question number three what would the results of the dexamethasone suppression test be like in patients with post-traumatic stress disorder option a normal option b exaggerated option c no suppression the answer to this question is exaggerated
Cortisol is a stress hormone however in patients with post-traumatic stress disorder there are very low levels of cortisol here’s how i think of it cortisol helps us cope with stress in patients with ptsd low levels of cortisol might probably be the reason why they find it very hard to cope with stress cortisol levels are already low in these patients by giving
Them dexamethasone we reduce the acth levels by negative feedback this will further decrease the cortisol levels in patients with ptsd hence the test is exaggerated in patients with post-traumatic stress disorder if you’re taking the usmle i highly recommend you to check the rapid review playlist out it has a lot of short videos with questions and explanations
Which are super important for the usmle if you have any topic that you want me to teach please mention them in the comments you can send me an email or text me on instagram if you want to get in touch thank you for watching and i’ll see you next time you
Transcribed from video
Dexamethasone Suppression Test: High dose vs Low dose | Cushing Syndrome | USMLE | MCQs By Ishwari Chandran
