Hypovitaminosis D masking hypercalcemia in primary hyperparathyroidism: case report

Hyperparathyroidism (HPTH) is the third most common endocrine disorder. Hypovitaminosis D affects up to 40% of the general population and about a third of hyperparathyroid patients. Such a combination may alter the classic presentation of HPTH. This report presents a premenopausal female with long history of osteoporosis, normocalcemia, and hypovitaminosis D who was initially diagnosed as secondary HPTH. After restoring vitamin D to normal using parenteral loading doses, the patient developed persistent mild to moderate hypercalcemia with persistent parathormone elevation consistent with primary HPTH associated with hypercalciuria and complicated with nephrocalcinosis. Imaging confirmed a left upper parathyroid adenoma and fulfilling several indications for surgery, the patient was operated restoring normocalcemia that was maintained for several years of follow-up. Hypovitaminosis D is common and may mask expected hypercalcemia in patients with primary HPTH, thus delaying diagnosis and proper intervention. Reevaluating patients initially diagnosed as hypovitaminosis D and secondary HPTH may reveal a masked diagnosis of primary hyperparathyroidism.