mrcem2-0573

mrcem2-0573

You evaluate a 45-year-old man with a history of difficult-to-control hypertension. His initial diagnosis was made after ambulatory blood pressure monitoring. He is currently taking Lisinopril 10 mg once daily and Amlodipine 10 mg once daily. Despite this treatment, his blood pressure today is 156/98. On examination, he appears normal and is otherwise in good health. A recent blood test shows the following results:
Sodium: 145 mmol/L (135-147 mmol/L)
Potassium: 3.2 mmol/L (3.5-5.5 mmol/L)
Urea: 6.3 mmol/L (2.0-6.6 mmol/L)
Creatinine: 88 mmol/L (75-125 mmol/L)
What is the MOST LIKELY diagnosis?