A 52-year-old woman presents to the outpatient clinic with a 3-month history of fatigue, bone pain, and polyuria. Serum calcium is 11.2 mg/dL (normal 8.5–10.5), phosphate 2.8 mg/dL (normal 2.5–4.5), and PTH 156 pg/mL (normal 15–65). Alkaline phosphatase is elevated at 92 U/L. Renal function is normal. What is the most appropriate next step in management?