SAT209 Metastatic Parathyroid Carcinoma And The Challenge Of Maintaining Calcium Balance

Disclosure: K.M. Tuna: None. S. Badour: None. E.P. Monsour: None. G. Acosta Garcia: None. D. Barb: None. Background: Parathyroid carcinoma is a rare malignancy representing less than 1% of all parathyroid disorders. Presentation is significant for highly elevated calcium (Ca) and parathyroid hormone (PTH) levels, and usually a palpable neck mass (>3cm). Diagnosis is often made after surgery based on histopathology findings. The primary treatment modality remains surgical, but there is no effective approach for metastatic disease. Case presentation: A 51-year-old woman initially presented with multinodular goiter and compressive symptoms in 2008. Workup showed an elevated Ca of 14.4 mg/dl (normal 8.4-10.2 mg/dl) and PTH of 502 pg/ml (normal 12-88 pg/ml) while albumin 4.3 g/dl (normal 3.5-5.2 g/dl) and normal thyroid function tests. Radioactive Iodine uptake scan showed a 4.4 cm cold nodule on the right inferior pole. Sestamibi scan showed increased left upper pole activity. The patient underwent total thyroidectomy with surgical exploration for parathyroid adenoma. Pathology showed right intrathyroidal parathyroid carcinoma with lymphovascular invasion. The patient was lost to follow-up until 2022 when she was admitted with severe hypercalcemic crisis (Ca 15.8 mg/dl, Albumin 3.9 g/dl, and PTH 805 pg/ml). The patient was treated with IV fluids, calcitonin, and multiple rounds of bisphosphonates, and was then maintained on high-dose cinacalcet due to refractory and recurrent hypercalcemia. Repeat Sestamibi and neck US were unremarkable, although CT chest showed a 1.3 cm nodule in the right lower lung lobe. This was not FDG- nor DOTATATE-avid on PET-CT. The patient underwent laparoscopic wedge resection of the right lung nodule, and the pathology was consistent with metastatic parathyroid carcinoma. Her Ca and PTH levels normalized immediately after surgery (PTH decreased from 883 to 27 pg/ml) suggesting possible remission. Prior to discharge, she was started on oral calcium and vitamin D due to dropping Ca levels and clinical signs of hungry bone syndrome. She was readmitted one month later for preexistent heart failure exacerbation and declining renal function. Her PTH was noted to be elevated again, although Ca remained normal, raising concern for recurrent or persistent disease. However, the patient’s renal impairment and lung effusion limited further imaging. Ca and PTH were monitored frequently during hospitalization and weekly after discharge. PTH levels peaked at 634 pg/ml and then dropped to 127 pg/ml without intervention. Ca remained in the normal range while on calcium citrate and calcitriol. Conclusion: Treatment of metastatic parathyroid carcinoma remains a challenge. Mortality is secondary to complications of hypercalcemia; therefore, controlling calcium levels should be the main therapeutic goal. Hungry bone syndrome should be considered after surgery. Metastatic disease may occur even after 20 years; thus, lifelong close monitoring is indicated. Presentation: Saturday, June 17, 2023