A 52-year-old man from Mumbai presents with progressive hypertension (160/95 mmHg), central obesity, easy bruising, and proximal muscle weakness. He has been on long-term oral prednisolone 20 mg daily for rheumatoid arthritis for 5 years. Laboratory studies show: fasting glucose 185 mg/dL, potassium 3.2 mEq/L, morning cortisol 18 μg/dL, ACTH 8 pg/mL (normal 10–50). A low-dose dexamethasone suppression test (1 mg overnight) shows cortisol of 16 μg/dL (normal <1.8). What is the most appropriate interpretation of these findings?