MON-849 - Parathyromatosis: A Rare and Challenging Etiology of Recurrent Hyperparathyroidism

Background: Parathyromatosis is a rare and challenging cause of recurrent and persistent hyperparathyroidism. It is characterized by multifocal hyperfunctioning parathyroid tissue scattered within the neck or mediastinum. Proposed mechanisms include seeding of parathyroid tissue following surgical disruption and persistence of embryologic rests. Genetic factors such as variants in the MEN1 gene may also play a role in the development of this condition.

Case Report: We report the case of a woman initially diagnosed with primary hyperparathyroidism in her early thirties. She experienced 2 relapses over a 15-year period. At initial presentation, imaging demonstrated focal sestamibi uptake consistent with a parathyroid adenoma, and she underwent right inferior parathyroidectomy with subsequent biochemical improvement. 10 years later, she presented with recurrent disease, including serum calcium of 13.5 mg/dL and parathyroid hormone level (PTH) of 257 pg/mL, prompting revision parathyroidectomy. 5 years after her second surgery, she developed severe recurrent hypercalcemia with serum calcium of 13.7 mg/dL and PTH level of 360 pg/mL. Neck ultrasound and sestamibi SPECT imaging were non-localizing. However, 4-dimensional computed tomography identified 2 lobulated enhancing lesions measuring up to 1.9 cm, abutting the left sternocleidomastoid and strap muscles. She tried medical therapy with cinacalcet briefly but did not respond well. Surgical intervention resulted in a marked intraoperative PTH decline from 555 pg/mL preoperatively to 56 pg/mL post-resection, along with resolution of her hypercalcemia. Histopathology revealed multiple nodules of hypercellular parathyroid tissue embedded within fibroadipose tissue and skeletal muscle, without features of malignancy, confirming parathyromatosis.

Conclusion: This case highlights the importance of maintaining a high index of suspicion for parathyromatosis in patients with recurrent hyperparathyroidism after prior parathyroid surgery. While complete surgical excision remains the primary treatment, recurrence is common and adjunct nonsurgical therapies including calcimimetic agents, antiresorptive agents, and in select cases, percutaneous ablation may play an important role in long-term biochemical control when disease is diffuse and/or unresectable. Genetic testing should also be offered to these patients.

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