Review Question - QID 216385

A 49-year-old man presents with 3 months of generalized weakness. He has had a chronic cough and a 20 pound unintentional weight loss over the past 6 months. He has a medical history significant for high blood pressure, hyperlipidemia, and seasonal allergies with no prior surgical history. He has no history of tobacco use. He moved from India 7 years prior to presentation. He currently lives in Oregon and has not left the west coast since moving. His temperature is 99°F (37.2°C), blood pressure is 100/70 mmHg, pulse is 76/min, and respirations are 16/min. His physical exam is significant for hyperpigmentation of the oral mucosa and temporal muscle wasting. Radiography of the abdomen demonstrates bilateral adrenal calcifications. Laboratory values are as follows:

Serum:
Na+: 130 mEq/L
Cl-: 96 mEq/L
K+: 5.2 mEq/L
HCO3-: 24 mEq/L
Morning cortisol: 2 ug/dL
30-minute cortisol during cosyntropin test: 8 ug/dL (normal > 18 ug/dL)
Morning adrenocorticotropic hormone (ACTH) concentration (serum): 80 pg/mL (normal 10-60 pg/mL)

Which of the following is the most appropriate next step in management?