Cushing's Disease and the Dexamethasone Suppression Test Flashcards
What hormone is primarily elevated in Cushing’s syndrome?
Cortisol
Which gland secretes cortisol?
The adrenal glands
What is the function of cortisol in the body?
Increases alertness, suppresses the immune system, reduces inflammation, inhibits bone formation, raises blood glucose, increases metabolism, and supports cardiovascular function.
What is the HPA axis?
The hypothalamic-pituitary-adrenal axis, which controls cortisol release.
What hormone does the hypothalamus release to stimulate ACTH production?
Corticotropin-releasing hormone (CRH)
What is the role of ACTH?
Stimulates the adrenal glands to release cortisol.
What is negative feedback in the HPA axis?
High cortisol levels inhibit CRH and ACTH release to maintain balance.
What does ‘exogenous steroids’ mean in the context of Cushing’s syndrome?
Steroids originating outside the body, like medications (e.g., prednisolone), that can suppress natural cortisol production.
What is Cushing’s disease?
A pituitary adenoma that secretes excessive ACTH, leading to high cortisol levels.
Name the causes of Cushing’s syndrome using the CAPE mnemonic.
Cushing’s Disease, Adrenal adenoma, Paraneoplastic syndrome, Exogenous steroids
What are some classic physical signs of Cushing’s syndrome?
Moon face, central obesity, abdominal striae, buffalo hump, proximal muscle wasting
What metabolic disturbances are seen in Cushing’s syndrome?
Hypertension, cardiac hypertrophy, type 2 diabetes, dyslipidemia, osteoporosis
Which feature is specific to excess ACTH production and not seen with adrenal adenomas or exogenous steroids?
Skin hyperpigmentation
What does the dexamethasone suppression test evaluate?
The ability of dexamethasone (a synthetic steroid) to suppress cortisol production via feedback inhibition.
What is the treatment for Cushing’s syndrome?
Surgical removal of the underlying cause (e.g., pituitary or adrenal tumor), adrenalectomy, or medical therapy like metyrapone.
When is dexamethasone administered for the suppression test?
At 10 p.m., with cortisol and ACTH measured the next morning.
What is the expected response in a healthy person after low-dose dexamethasone?
Suppression of cortisol levels.
What does it indicate if cortisol remains high after a low-dose dexamethasone test?
Cushing’s syndrome or Cushing’s Disease is likely present.
What result suggests Cushing’s disease (pituitary adenoma) after a high-dose test?
Cortisol is suppressed and ACTH decreases.
What result suggests an adrenal tumor as the cause of Cushing’s syndrome?
High cortisol with low ACTH after a high-dose test.
What result suggests ectopic ACTH production (e.g., from lung cancer)?
High cortisol with high ACTH that is not suppressed by high-dose dexamethasone.
Why doesn’t dexamethasone suppress cortisol in adrenal or ectopic causes of Cushing’s?
Because the cortisol is being produced independently of the pituitary ACTH pathway.
