Method for differentially diagnosing ACTH-dependent cushing's syndrome

A method of concurrently treating Cushing's syndrome and obtaining a measurement indicative of differential diagnosis of adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome in a patient where the differential diagnosis is between ectopic ACTH syndrome and Cushing's Disease, the method comprising the steps of:

• administering a dose of glucocorticoid receptor antagonist (GRA) to a patient with Cushing's syndrome and an elevated ACTH level, wherein the amount of GRA administered to said patient is sufficient to increase ACTH from the pituitary gland by at least two-fold in persons with normal Hypothalamus Pituitary Adrenal (HPA) function;
• then, at least two hours following said administration,
• removing from the patient a venous sample from an inferior petrosal sinus and a venous sample from a peripheral vein, and
• determining the ACTH concentration ratio from the patient, wherein the ACTH concentration ratio is derived from the ACTH concentrations in fluid obtained from either the left or right inferior petrosal venous sinus and from fluid obtained from a periphery venous sample;
• and
• determining the prolactin ratio from the patient, wherein the prolactin ratio is derived from the prolactin level measured in fluid obtained from either the left or right inferior petrosal sinus and from the prolactin level measured in fluid obtained from a peripheral vein,
• wherein both i) a prolactin ratio of greater than 1.8 for the prolactin level from the inferior venous sinus sample over the periphery venous sinus sample, and ii) an ACTH concentration ratio of greater than 3 for the ACTH concentration from the inferior venous sinus sample over the periphery venous sinus sample together is indicative of Cushing's disease.