Correct!
3. Low-dose dexamethasone suppression test
Adrenal vein sampling is typically employed in the setting of primary hyperaldosteronism to determine if aldosterone production is unliteral or bilateral; surgical therapy is effective for the former. Inferior petrosal sinus sampling is an invasive procedure in which adrenocorticotropic hormone (ACTH) levels are sampled from pituitary gland venous drainage and compared with blood ACTH levels to distinguish a pituitary cause from an ectopic source of ACTH-dependent Cushing syndrome. While this procedure may play a role in this patient’s evaluation, it is invasive and premature at this point. The diagnosis of Cushing syndrome should first be confirmed, for which the low-dose dexamethasone suppression test is appropriate. Selective venous sampling (parathyroid venous sampling) is an invasive procedure used for detecting elevated intact parathyroid hormone in the thyroid veins and/or internal jugular and brachiocephalic veins, typically in the context of recurrent or persistent hyperparathyroidism following surgery. Arterial stimulation and venous sampling refer to a procedure in which hepatic venous sampling is conducted after calcium is administered to assess pancreatic endocrine neoplasms.
The patient underwent low-dose dexamethasone suppression testing, which revealed a morning cortisol level of 36.5 mcg/dL (normal, 7-25 mcg/dL) following a dose of dexamethasone the previous evening, with a morning ACTH level of 37 pg/mL (normal, 10-60 pg/mL). A 24-hour urinary free cortisol measurement was abnormally elevated. Testing for coccidioidomycosis was unrevealing.
Which of the following represents the most appropriate next step for the patient’s management? (Click on the correct answer to be directed to the fifth of twelve pages)