SUN-873 - Parathyromatosis Following Parathyroidectomy for Primary Hyperparathyroidism: A Rare Cause of Persistent Disease

Parathyromatosis is a rare and challenging cause of persistent or recurrent primary hyperparathyroidism (PHPT), most often resulting from iatrogenic dissemination of parathyroid tissue during surgery. Ectopic mediastinal location and cystic adenoma morphology may increase the risk of capsular rupture and subsequent parathyromatosis.
An 86-year-old woman presented with symptomatic hypercalcemia. Laboratory evaluation showed markedly elevated serum calcium (16.1 mg/dL) and intact parathyroid hormone (PTH) (594.7 pg/mL), consistent with PHPT. Esophageal ultrasound and Computed Tomography of the chest revealed a large posterior mediastinal mass inseparable from the esophagus and a cystic lesion inseparable from the thyroid lobe. Biopsy confirmed parathyroid tissue. The patient underwent video-assisted thoracoscopic partial resection and unroofing of the presumed paraesophageal cyst. She subsequently developed recurrent hypercalcemia with persistently elevated serum PTH and elevated PTH levels in pleural fluid, consistent with parathyromatosis. Given the diffuse nature of disease, she was managed medically with a calcimimetic agent, bisphosphonates, and dialysis, achieving biochemical control.
This case highlights parathyromatosis as an uncommon but important cause of persistent PHPT following parathyroid surgery. Mediastinal ectopic adenomas and cystic morphology increase surgical complexity and predispose to capsular rupture and parathyroid tissue seeding. Early recognition, meticulous surgical technique, and preventive strategies are essential, as definitive surgical cure is often difficult once parathyromatosis develops.

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