What is the most appropriate next step in management?

A 44-year-old man was referred for investigation of cortisol excess. He had poorly controlled hypertension, and a long history of type 2 diabetes mellitus with retinopathy and peripheral neuropathy. His medication comprised aspirin, ramipril, atenolol,

carbamazepine, metformin and simvastatin.

Initial investigations:

serum cortisol (09.00 h)350 nmol/L (200C700)

serum cortisol (22.00 h)48 nmol/L (50C250)

overnight dexamethasone suppression test (after 1 mg dexamethasone):

serum cortisol93 nmol/L (<50)

24-h urinary free cortisol (day 1)225 nmol (55C250)

24-h urinary free cortisol (day 2)200 nmol (55C250)

24-h urinary free cortisol (day 3)185 nmol (55C250)

What is the most appropriate next step in management?
A . CT scan of adrenal glands
B . dexamethasone-suppressed corticotrophin-releasing hormone test
C . high-dose 48-h dexamethasone suppression test
D . MR scan of pituitary
E . reassure and discharge