CUSHING'S DISEASE. VS CUSHING'S SYNDROME.

CUSHINGS DISEASE VS CUSHINGS SYNDROME AND DEXAMETHASONE SUPPRESSION TEST:

Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary gland to suppress the secretion of adrenocorticotropic hormone (ACTH). Specifically, dexamethasone binds to glucocorticoid receptors in the anterior pituitary gland, which lie outside the blood-brain barrier, resulting in regulatory modulation.

Low-dose and high-dose variations of the test exist.The test is given at low (usually 1–2 mg) and high (8 mg) doses of dexamethasone, and the levels of cortisol are measured to obtain the results.

A low dose of dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production. 

A high dose of dexamethasone exerts negative feedback on pituitary neoplastic ACTH-producing cells (Cushing's disease), but not on ectopic ACTH-producing cells or adrenal adenoma (Cushing's syndrome).