Recurrent Nephrolithiasis in a Patient With Hypercalcemia and Normal to Mildly Elevated Parathyroid Hormone

A 42-year-old man was referred to our stone clinic for recurrent episodes of symptomatic nephrolithiasis. Spontaneous stone passages occurred at the ages of 25, 40, and 42 years with one need for endoscopic stone removal. Calculi were composed of 100% calcium oxalate monohydrate. The patient had not taken any medication or supplements. Increased fluid intake was the only intervention for stone prevention. Metabolic work-up at presentation revealed mild hypercalcemia and normal to mildly elevated intact parathyroid hormone, even after repletion with oral 25-hydroxyvitamin D. 1,25-Dihydroxyvitamin D level and 24-hour urinary calcium excretion were within normal ranges (Table 1). Physical examination was unremarkable. Family history was negative for nephrolithiasis or hypercalcemia. • What are the main differential diagnoses of hypercalcemia with an elevated PTH level in this patient? • What tests help to distinguish between these two entities? • Which additional studies help to verify the diagnosis