PSAT205 A Case of Persistent Primary Hyperparathyroidism Secondary to an Occult Supernumerary Parathyroid Adenoma

BACKGROUND: Persistent primary hyperparathyroidism accounts for the vast majority of patients who require reexploration. With the advancements in preoperative localization, surgical outcomes have improved over time. However, in patients with failed reoperative parathyroid exploration, an occult supernumerary parathyroid adenoma should be considered. CLINICAL CASE: A 60 year-old female diagnosed with primary hyperparathyroidism presented with recurrent nephrolithiasis, osteoporosis and declining eGFR. Initial laboratory evaluation showed elevated serum calcium (1.54 mmol/L, normal 1.09-1.30) and intact PTH (146 pg/mL, normal 18.50-88.0). 99mTc-sestamibi scintigraphy showed a sestamibi-avid focus in the inferior aspect of the right lobe hence, she underwent radionuclide-guided focused right parathyroidectomy. Post-operatively, her intact PTH level was still elevated (171.2 pg/mL). Histopathologic examination showed a normocellular parathyroid gland and a multifocal papillary thyroid carcinoma. The failed 1st surgery was attributed to the false positive scintigraphy from the papillary thyroid carcinoma. She then underwent total thyroidectomy with central neck dissection and 3½ parathyroidectomy with intraoperative parathyroid hormone assay. However, serial PTH monitoring after exploration and parathyroidectomy failed to decrease the PTH level by 50%. Histopathologic examination showed normocellular parathyroid glands. The bilateral carotid sheath, retropharyngeal region and superior mediastinum were explored but no ectopic parathyroid tissues were seen. Post-operatively, calcium and PTH were still elevated (1.48 mmol/L and 200.5 pg/mL, respectively). FDG PET CT imaging failed to show any ectopic parathyroid gland or adenoma. No further surgical intervention was done and she was medically managed with Cinacalcet 30 mg twice daily. 15 months after her parathyroid gland exploration, calcium and PTH were still elevated (1.46 mmol/L and 156.80 pg/mL, respectively). F18 Choline PET CT imaging was done showing a small hypoenhancing persistently FCH-positive focus in the left thyroid bed and sliver of enhancing tissue relating to a parathyroid adenoma. CONCLUSION: This case highlights the diagnostic and therapeutic challenges in a patient with persistent primary hyperparathyroidism after a failed 2nd surgery. Occult parathyroid adenomas can cause significant symptoms regardless of its size and its imperceptible nature on imaging. The role of medical management is emphasized in this case when surgical management was not possible. Furthermore, re-evaluation for growth of the possible occult parathyroid adenoma should be done, which in this case took 15 months until its detection. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.