Challenges in the differential diagnosis of hypercalcemia: A case of hypercalcemia with normal PTH level

The hypercalcemias are a common and heterogeneous group of disorders, ranging from the occasional detection of a high level of serum calcium to a life-treating condition. In a patient presenting with hypercalcemia, a differential diagnosis can be established easily by measuring serum calcium and parathyroid hormone (PTH) concentrations. We describe the case of an 83-year-old man presenting with a severe symptomatic hypercalcemia with high-normal PTH level due to the coexistence of primary hyperparathyroidism and malignancy-associated hypercalcemia. The presence of two conditions producing hypercalcemia was revealed only during in-hospital stay and after the administration of an intravenous bisphosphonate, when the PTH concentration increased rapidly after bisphosphonate treatment with a decrease in serum calcium. The occurrence of two conditions producing hypercalcemia is a rare event in the literature, and should be considered in the presence of an abnormally high serum calcium level associated with normal or high-normal PTH, in order to establish a correct diagnosis and appropriate interventions.