Double Trouble: A Case of Primary Hyperparathyroidism and Humoral Hypercalcemia of Malignancy Secondary to Epithelioid Angiosarcoma Occurring in a Single Patient

ABSTRACT Objective: Primary hyperparathyroidism (PHPT) is the most common cause of hypercalcemia and is the third most common endocrine disorder. Hypercalcemia occurs in an estimated 10 to 30% of patients with cancer, with humoral hypercalcemia of malignancy (HHM) accounting for 80% of these cases. It is very uncommon for both of these causes of hypercalcemia to occur in a single patient. Methods: We describe the case of a patient who presented with PHPT and probable concurrent HHM. Results: A 72-year-old male presented with severe hypercalcemia. A single parathyroid adenoma was identified and resected. The patient returned to the hospital 2 weeks later with recurrent hypercalcemia and a lowered parathyroid hormone concentration. Upon workup a right hip mass was detected at the site of a prior hip arthroplasty and was thought to represent periprosthetic osteolysis or pseudotumor. A biopsy revealed malignancy consistent with epithelioid angiosarcoma. We discuss risk factors associated with PHPT and HHM and the differences in their clinical presentations. Conclusion: This case highlights the importance of performing a thorough workup and differential diagnosis with all patients presenting with hypercalcemia, and in particular with recurrent hypercalcemia. Abbreviations: HHM = humoral hypercalcemia of malignancy HPT = hyperparathyroidism PHPT = primary hyperparathyroidism PTHrP = parathyroid hormone-related peptide