Review Question - QID 215047

A 45-year-old woman presents to the clinic with hypertension and weakness. Her home blood pressure readings are consistently above 150/90 mmHg despite her being on chlorthalidone, amlodipine, and lisinopril. She has found it increasingly difficult to climb stairs over the past month. Her medical history includes diabetes mellitus, for which she takes metformin. Her temperature is 98.6°F (37.0°C), blood pressure is 154/98 mmHg in the right arm and 158/94 mmHg in the left arm, pulse is 84/min, and respirations are 16/min. Her body mass index (BMI) is 29.4 kg/m^2. Physical exam reveals a woman with thick, dark hair above her upper lip and a posterior fat pad over her neck. Her 24-hour urine cortisol excretion is 345 mcg (reference range: 4-40 mcg/24 hours). A repeat 24-hour urine cortisol excretion is 362 mcg. Which of the following is the most appropriate next step in management?