Co-Existence of Primary Hyperparathyroidism due to Multiple Endocrine Neoplasia 1 in a Hypercalcemic Patient with Graves Disease

ABSTRACT Objective: Hypercalcemia in a patient with Graves disease can occur in up to 22% of cases. The mechanism is thought to be increased bone resorption. There are more rare causes of hypercalcemia in these patients with hyperthyroidism, such as hyperparathyroidism, which occurs in less than 1% of patients. We describe a rare occurrence of primary hyperparathyroidism due to multiple endocrine neoplasia type 1 (MEN 1) in a Graves disease patient presenting with hyperthyroidism and hypercalcemia. Methods: The patient initially presented with a 3-week history of nausea, vomiting, and abdominal pain. She also had an 8-week history of a 12-pound weight loss. She was diagnosed with hyperthyroidism secondary to Graves disease and was noted to have concurrent hypercalcemia. She was diagnosed with primary hyperparathyroidism. The patient underwent subtotal thyroidectomy and total parathyroidectomy with forearm autotransplantation. Subsequent genetic testing confirmed the diagnosis of MEN 1. Results: A review of the literature was conducted to identify previous studies pertaining to concurrent hypercalcemia in hyperthyroid patients, focusing on reports related to their diagnosis and management. Conclusion: Co-existing primary hyperparathyroidism due to MEN 1, although rare, should be considered in a patient with hyperthyroidism and hypercalcemia. A thorough evaluation is necessary to avoid a delay in the correct diagnosis and treatment of the underlying conditions. Clinicians should be aware of the rare occurrence of primary hyperparathyroidism due to MEN 1 in a Graves disease patient presenting with hyperthyroidism and hypercalcemia. Abbreviations: MEN 1 = multiple endocrine neoplasia type 1; PTH = parathyroid hormone