Mediastinal Parathyroid Adenoma Mimicking Cancer Metastatic to Bone

ABSTRACT Objective: Mediastinal parathyroid adenomas are rare in clinical practice. We report a case that mimicked cancer metastatic to bone on initial workup to increase awareness of this differential diagnosis in the evaluation of patients presenting with multiple foci of uptake on technetium bone scanning without an established primary neoplasm. We also outline other diagnostic pitfalls that may be encountered in the workup and management of this uncommon condition. Methods: A 26-year-old man presented with a several-month history of back and pelvic pain. Initial plain radiography showed multiple lytic lesions in the pelvis. Technetium bone scanning revealed multiple foci of increased uptake in the thoracic vertebrae, ribs, clavicles, pelvis, and extremities. Results: A computed tomography (CT) scan demonstrated a mediastinal mass and an initial diagnosis of metastatic disease from a mediastinal primary malignancy was entertained. Further workup revealed markedly elevated serum ionized calcium of 1.97 mmol/L (normal, 1.19 to 1.31 mmol/L) and parathyroid hormone (PTH) of 154.8 pmol/L (normal, 2.0 to 9.4 pmol/L). Parathyroid scintigraphy showed intense tracer accumulation in the anterior mediastinal mass. A median sternotomy was performed and histopathology was consistent with a parathyroid adenoma. Postoperatively, the patient's ionized calcium and PTH levels normalized and pain resolved. Conclusion: This case illustrates two clinical pearls: (1) brown tumor secondary to hyperparathyroidism is an important differential in the evaluation of patients presenting with widespread lytic bone lesions on CT or multiple foci of uptake on bone scan; and (2) the mediastinum is a rare location but should be considered in the workup of primary hyperparathyroidism. Abbreviations: CT computed tomography; PTH parathyroid hormone