Long-term follow-up revealed hypocalciuric hypercalcemia in a patient initially treated for primary hyperparathyroidism

Abstract

In patients with hypercalcemia and normal or mildly elevated parathyroid hormone (PTH) levels, distinguishing primary hyperparathyroidism (PHPT) from hypocalciuric hypercalcemia (HH) is crucial. We describe a 70-year-old woman who underwent parathyroidectomy for PHPT at 58 years old. Despite surgery, she remained asymptomatic with persistent hypercalcemia, normal phosphate levels, 25-hydroxyvitamin D, renal function, and mildly elevated PTH levels. Serial imaging suggested recurrent parathyroid disease, and subtotal parathyroidectomy demonstrated parathyroid hyperplasia. Although serum calcium and PTH levels initially normalized, hypercalcemia later recurred with normal PTH levels. Twenty-four-hour urinary calcium excretion was markedly low, and the calcium-to-creatinine clearance ratio (CCCR) was consistent with HH. No pathogenic variant was detected in the calcium-sensing receptor gene (CASR). At 84 years old, the patient remained asymptomatic. Long-term follow-up supported the diagnosis of HH despite negative CASR testing. This case underscores the importance of measuring 24-hour urinary calcium excretion and calculating the CCCR in patients with hypercalcemia, particularly in asymptomatic individuals, before considering parathyroid surgery.