6396 Recurrent hyperparathyroidism due to parathyromatosis

Abstract Disclosure: A. Valenciaga: None. M.N. Rayan: None. S.W. Ing: None. Background: Parathyromatosis is a rare cause of hyperparathyroidism. It refers to numerous parathyroid tissue foci within the neck and mediastinum, arising from the expansion of embryologic parathyroid tissue or due to the dissemination of parathyroid cells during surgical resection of abnormal parathyroid glands. Here, we describe the case of a patient who underwent multiple medical and surgical interventions to manage recurrent hyperparathyroidism secondary to parathyromatosis. Clinical Case: A 28-year-old male with no significant past medical or family history presented to the ED in 2012 after experiencing malaise for months and a syncopal episode. Labs showed serum calcium (Ca) of 18.1 mg/dL and parathyroid hormone (PTH) of 1199 pg/mL. Sestamibi scan was non-localizing, but ultrasound and CT scan identified a 1.5 cm nodule posterior to the right thyroid lobe, concerning for a parathyroid adenoma. He underwent surgical excision of this nodule which revealed benign parathyroid tissue on final pathology. He felt well for a few years, but symptoms recurred in 2017 with hypercalcemia, elevated PTH, and nephrolithiasis. Sestamibi scan was again non-localizing. He underwent a more extensive neck surgery where the right thyroid and a left central neck soft tissue specimen showed atypical parathyroid tissue on final pathology, favoring the diagnosis of parathyromatosis. He underwent a third surgery in 2019 after symptoms recurred, with more hypercellular parathyroid tissue identified in the neck. He remained asymptomatic again until 2021, when his Ca rose to 18.2 mg/dL with PTH of 2159 pg/mL while Sestamibi showed uptake in the left thyroid. He then underwent a fourth, very extensive neck surgery. Pathology revealed at least 36 nodules of parathyroid tissue embedded in skeletal muscle and fibroadipose tissue. No significant cytological atypia was found favoring a diagnosis of parathyromatosis rather than a carcinoma. Post-op PTH improved to 667 pg/mL and calcium levels dropped to 6.2 mg/dL. PTH dropped to 132 pg/mL later that year. A few months later, his levels started to rise, with Ca peaking at 13.3 mg/dL and PTH at 1260 pg/mL in 2023. Sestamibi scan was non-localizing. He had taken cinacalcet but was dose-limited due to nausea. Zometa was also given without good response. We then initiated monthly denosumab 120 mg with improvement in Ca and PTH levels. Conclusions: This is a rare and challenging case, both to diagnose and treat. Due to the scarcity of cases, there are no well-defined clinical guidelines for diagnosis and management. While a great tool, Sestamibi scans in his case have been negative or not completely inclusive of foci that were later found in surgical pathology. Surgery is a key part of management, but patients may not achieve permanent remission, making medical therapy also essential in controlling Ca and PTH levels, and a multidisciplinary approach key in management of these cases. Presentation: 6/2/2024