A 45-year-old woman presents with central obesity, purple striae, proximal muscle weakness, and hypertension. Overnight 1 mg dexamethasone suppression test shows serum cortisol of 9 µg/dL. What is the next best diagnostic step?
A
CT scan of adrenal glands
B
Plasma ACTH measurement
C
Inferior petrosal sinus sampling
D
Start ketoconazole therapy