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can any1 explain d mechanism behind d dexamethasone suppression test used to differentiate pituitary, adrenal n other ACTH producing conditions leading to cushing's syndrome......:toosad: :indifferent:
I can't get why d cortisol level varies with dose in all these cases...too confusing....:eek: :eek:
 

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can any1 explain d mechanism behind d dexamethasone suppression test used to differentiate pituitary,adrenal n other ACTH producing conditions leading to cushing's syndrome......:toosad: :indifferent:
i cant get why d cortisol level varies with dose in all these cases...too confusing....:eek: :eek:
ACTH controls Cortisol

Dexamethasone = "Super Cortisol"

Dexamethasone provides negative feedback to the pituitary to suppress the secretion of ACTH.

Low Dose test
--------------
Suppress:
1- Normal
2- Obese (adipose tissue preduces cortisol)
3- Depression (stress produces cortisol)

No Suppress after low dose- have Cushings, do a high dose test

High Dose Test "PAL"

Suppress:
Pituitary tumor- ACTH

Not Suppress:
1- Adrenal adenoma- Cortisol
2- Lung cancer- ACTH, SIDAH, cushings moon facies
 

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Dexamethasone suppression test
screening tests for endogenous cushing syndrome include
overnight low dose dexamethasone suppression test
24-hr urine free cortisol
administration of dexamethasone, potent glucocorticoid, should suppress acth and cortisol levels in normal individuals
however, pts with endogenous cushing syndrome don't suppress serum cortisol levels following administration of low dose dexamethasone
typically, in pts with cushing's ds, cortisol levels don't suppress with low dose dexamethasone but do suppress with high-dose dexamethasone
the test is useful in differentiating cushing ds from cushing synd caused by ectopic acth production
when there is ectopic source of acth, acth levels are typically markedly elevated, and there is no suppression of acth or cortisol with even high-dose dexamthasone​
 
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