[Hyperparathyroidism due to parathyroid carcinoma located in the mediastinum]

Parathyroid gland carcinoma is a rare cause of primary hyperparathyroidism. The authors discuss the case of a 56-year-old man who presented with hypercalcemia and multiple bone lesions suggestive of tumor metastases. Laboratory and radiological investigations revealed primary hyperparathyroidism in a patient with evidence of osteitis fibrosa cystica, sustained by carcinoma of a mediastinal parathyroid gland. Early titration of parathyroid hormone (PTH) levels in all patients with hypercalcemia of unclear cause is important for early diagnosis of cases that are tumor-sustained and prevention of the most severe complications. The role of immunostaining with anti-PTH antibodies in demonstrating parathyroid gland tissue in ectopic and/or non-functioning primary tumors, as well as metastases, is also discussed.