Free nephrology board questions: CKD Bone Disease

A 76-year-old woman with ESRD is seen during dialysis rounds. She has been treated with in-center HD via a left upper extremity arteriovenous fistula for 3 years. A recent fall resulted in fracture of her hip, which was surgically repaired. Her home medications include cholecalciferol, cinacalcet, sevelamer, and calcitriol. Bone densitometry shows a T-score of -2.7. Laboratory data: PTH 614 pg/mL (reference 130–585, dialysis patients); alkaline phosphatase 113 U/L (30–120); 25-hydroxyvitamin D 32 ng/mL (30–60); phosphorus 4.2 mg/dL (3.0–4.5); calcium 8.7 mg/dL (8.6–10.2); albumin 3.4 g/dL (3.5–5.5). Which ONE of the following is the MOST appropriate next step in management?

A 66-year-old man with ESRD due to analgesic nephropathy has received HD via a left forearm AVF for 14 years. Over the last year, he has developed pain and stiffness in both shoulders. The pain is located anterolaterally and is aggravated by abduction of the shoulders. He also has neck pain and tingling in both hands, especially at night. Examination of shoulders reveal mild tenderness to palpation and protuberance of soft tissue above the shoulders, more prominent on the left. There is no tenderness or warmth. Radiography of the shoulders shows bone cysts with sclerotic margins that have grown in size compared with images obtained 6 months ago. Electromyography and nerve conduction studies show results consistent with bilateral carpal tunnel syndrome. Which of the following diagnostic tests is most likely to identify the cause of this patient’s shoulder pain?