Recurrent Kidney Stones and Normocalcemic Hyperparathyroidism: A Report of Two Cases

Introduction: Normocalcemic hyperparathyroidism is a risk factor for the development of kidney stones and can be challenging to identify. We report two patients with recurrent nephrolithiasis who were diagnosed with normocalcemic primary hyperparathyroidism. Case Description: Patient 1: A 73 year old man with recurrent calcium oxalate nephrolithiasis presents to a nephrology based kidney stone prevention clinic. He has spontaneously passed one kidney stone and required one stone removal procedure. His most recent kidney ultrasound is negative for renal calculi. His 24 hour urine chemistry results are notable for a urine calcium level of 369 mg (< 250 mg/d). He is found to have a PTH of 79 ng/L (18-90 ng/L) and a serum calcium of 10.1 mg/dL (8.6-10.2 mg/dL). A parathyroid ultrasound and nuclear medicine scan are consistent with a parathyroid adenoma for which he undergoes a parathyroidectomy procedure. Subsequent lab testing demonstrates resolution of hypercalciuria (67 mg/d) and reduction in both the PTH (30 ng/L) and serum calcium levels (9.3 ng/dL). Patient 2: A 65 year old man with recurrent calcium nephrolithiasis presents to a nephrology based kidney stone prevention clinic. He has spontaneously passed one kidney stone and required four stone removal procedures. His most recent kidney ultrasound is notable for multiple bilateral non-obstructing calculi. His 24 hour urine chemistry results are notable for a urine calcium level of 562 mg. He is found to have a PTH of 125 ng/L and a serum calcium of 9.7 mg/dL. A parathyroid ultrasound and nuclear medicine scan are consistent with a parathyroid adenoma for which he undergoes a parathyroidectomy procedure. Subsequent lab testing demonstrates resolution of hypercalciuria and reduction in both the PTH and serum calcium levels. Discussion: Primary hyperparathyroidism is commonly diagnosed following biochemical work up for patients found to have hypercalcemia and is a risk factor for the development of hypercalciuria and calcium based kidney stones. More rarely, patients with primary hyperparathyroidism will be diagnosed after presenting with normal serum calcium and variable PTH levels. Establishing a diagnosis of normocalcemic hyperparathyroidism is more challenging and warrants consideration in patients with unexplained hypercalciuria along with PTH levels elevated out of portion to serum calcium levels.