A Case of Active Sarcoid Mimicking a Mediastinal Parathyroid Adenoma on Tc-99m Sestamibi Imaging

A 45-year-old man with a history of parathyroidectomy with a tissue implant in his forearm to treat hyperparathyroidism developed recurrent hyperparathyroidism with a parathyroid hormone level > 3,000 pcm/L. Dual-phase Tc-99m sestamibi imaging was interpreted as showing a persistent retrosternal focus consistent with a mediastinal parathyroid adenoma. The suspected tissue was resected by mediastinoscopy, and pathologic examination revealed chronic inflammatory and granulomatous mediastinal lymph nodes consistent with active sarcoidosis. The patient's parathyroid hormone level promptly returned to normal after removal of parathyroid tissue from his forearm implant, which was markedly hyperplastic on histologic examination.