A 42-year-old woman presents to your office complaining of several months of weight gain, menstrual irregularity, increased urination and increased abdominal girth. A detailed review of systems reveal irritability, insomnia, mood changes, difficulty standing up from a seated position, difficulty climbing stairs, and blurry vision. She is also distressed because of grown hair on her chin. Her only current medication is naproxen for menstrual-related pains. While speaking with her, you note that she has moon facies and increased fat pads on the back of her neck. Her temperature is 98.2 °F, heart rate is 89 beats/min, blood pressure is 168/99 mm Hg, respirations are 19 breaths/min, and oxygen saturation is 97% on room air. On examination, she is obese, with a plethoric appearance. Her abdomen is obese. Her arms and legs are thin. There is muscle wasting. There are prominent purplish striae over the abdomen. There are multiple bruises over both lower legs. You order some laboratory tests which yielded the following results. Lab test Test result Reference range Serum cortisol (0800 hr) 134 μg/dL 4.5–23 μg/dL Urinary free cortisol (random) 240 μg/dL <100 μg/dL Plasma ACTH (0800 hr) 2 pg/mL 10–60 pg/mL High-dose dexamethasone suppression test Serum cortisol (0800 hr) Fails to suppress Serum glucose 198 Random, non-fasting: <140 mg/dL Bicarbonate (HCO₃⁻) 38 mEq/L 22 - 28 mEq/L Which of the following is the most likely diagnosis in this patient?
