SAT208 Hypercalcemic Crisis In Metastatic Parathyroid Carcinoma: An Unusual Presentation Of A Rare Endocrine Disease

Disclosure: A. Barnett: None. T. Sliker: None. R.J. Harper: None. G. Elshimy: None. Introduction: Hypercalcemia can be life-threatening with a wide differential, including parathyroid carcinoma (PC), which accounts for only 0.005% of all malignancies in the U.S. Maintaining an index of suspicion for PC in PTH-mediated hypercalcemia is vital for improving long-term survival and outcomes. Frozen section can be misleading when PC is suspected. We describe a case of hypercalcemia due to recurrent metastatic PC 9 years after initial diagnosis. Case: A 57-year-old male presented for endophthalmitis and altered mentation. Records revealed primary hyperparathyroidism with calcium 11.7 mg/dL, PTH 337 (11.1-79.5pg/mL), and 24-hour urine calcium 810 mg/day. Sestamibi showed right lower parathyroid adenoma and a possible right upper parathyroid adenoma. Right superior parathyroidectomy revealed PC invasive into adipose tissue, increased vascularity and positive margins. A hemithyroidectomy and central neck dissection was performed with intraoperative report noting normal-appearing right inferior parathyroid affixed to thyroid, confirmed by frozen section biopsy. The right inferior parathyroid was minced and re-implanted into the right strap muscle. Patient did not return for follow-up. Recent admission labs showed calcium 15.2 mg/dL, ionized calcium 6.8 (4.5-5.3mg/dL), PTH 546 pg/mL, creatinine 1.54 mg/dL, 25-OH vitamin D 21.64 ng/mL, and phosphorus 1.9 mg/dL. He was treated with intravenous fluids, zoledronic acid, and calcitonin. Due to a high suspicion of locally recurrent or metastatic PC, further imaging obtained. A Neck CT and US showed no abnormalities of right surgical bed or cervical lymphadenopathy. Sestamibi revealed a right lower lung lobe nodule, measuring 2.3cm, with intense immediate and delayed uptake concerning for metastatic or primary lung neoplasm and mild focal retention in the right paratracheal region, suspicious for tumor recurrence. PTHrP was negative. He underwent video-assisted thoracoscopic right lower lobectomy that showed an ovoid, well-circumscribed 2.5 x 2.3 x 2.3cm tumor, which stained positive for PAX-8 and synaptophysin, consistent with PC. Discussion: Clinicians should suspect PC in cases with severe hypercalcemia or absolute PTH above 500mg/dL to allow for better surgical planning. Complete en bloc resection is the standard treatment to improve long-term outcomes and reduce disease recurrence. Diagnosis of PC following incomplete surgical resection has increased recurrence rates of greater than 50%. Our patient’s recurrence was 9 years after diagnosis, but most recurrences occur within 2-3 years and occasionally more than 20 years later. The ipsilateral parathyroid was re-implanted based on frozen section results in this patient, which may have been misleading. Frozen sections of parathyroid tissue are notoriously difficult to distinguish normal parathyroid versus PC and only diagnostic in 15% of cases as described in one case series. To reduce the risk of recurrent disease, physicians shouldn’t entirely depend on these results when there is high suspicion for PC. Presentation: Saturday, June 17, 2023