A 46-year-old woman presents with progressive weight gain, fatigue, proximal muscle weakness, and easy bruising over 6 months. She has developed facial rounding and purple abdominal striae. Her blood pressure is 168/96 mmHg. She is not taking corticosteroids.

Test results show:

• Random glucose: 11.8 mmol/L
• Potassium: 3.1 mmol/L
• An overnight low-dose dexamethasone suppression test fails to suppress serum cortisol