RF05 | PSUN364 A Rare Case of Bilateral Parathyroid Carcinoma in the Setting of Multiple Endocrine Neoplasia Type 1

BACKGROUND: Multiple Endocrine Neoplasia type 1 (MEN1) is an autosomal dominant disorder classically characterized by parathyroid gland tumors, anterior pituitary adenomas, and tumors of the gastro-entero-pancreatic tract. The majority of MEN1 cases involving lesions of the parathyroid gland causing hyperparathyroidism are almost always benign. It is extremely rare for hyperparathyroidism to be caused by parathyroid carcinomas. We report a very rare case of parathyroid carcinoma presenting in MEN1 syndrome. CASE REPORT: We present the case of a 45 year old male with a history of untreated hypertension, nephrolithiasis, and CKD, who became suddenly unresponsive, was intubated, and found to have a severe acute intraparenchymal hemorrhage secondary to severe hypertension on Head CT. Secondary causes of hypertension were ruled out, with renin activity, aldosterone levels, and urine metanephrines unremarkable; abdominal ultrasound with doppler was also negative for renal artery stenosis. Stroke protocol was initiated, with CTA Head negative for any acute findings. However, CTA Neck showed bilateral large nodules posterior to the thyroid lobes measuring 4.0×3.2 cm on the right and 3.9×2.5 cm on the left, with mass effect on the thyroid and adjacent carotids. Routine labs showed hypercalcemia of 13.3 (8.4-10.2 mg/dL) in the setting of elevated PTH levels of 1085 (15-65 pg/mL), with repeat PTH level of 1106 confirming primary hyperparathyroidism. Other causes of hypercalcemia were investigated, with levels of Calcitonin and Calcitriol/1,25 vitamin D within normal limits, but a decreased level of 25 hydroxy vitamin D of <12.8 (30-100 pg/mL). Maxillofacial CT was negative for any ossifying fibromas, ruling out jaw tumor syndrome. CT Abdomen showed hyperdense nodular areas in the pancreas, and MRI Brain was negative for any discrete pituitary gland lesions. Thyroid US was performed and revealed mixed cystic and solid masses posterior to both lobes of the thyroid; as a result, FNA of the thyroid and posterior mass was done, confirming hypercellular parathyroid tissue and benign thyroid tissue. Due to high suspicion for parathyroid carcinoma, the patient underwent a parathyroidectomy, with pathology confirming bilateral parathyroid carcinoma. Genetic testing was positive for MEN1, with a frameshift variant mutation of c.1299_1312del (p.Val434Leufs*10). CONCLUSION: This is a very rare case of bilateral parathyroid carcinoma presenting in MEN1. To the best of our knowledge, this genetic mutation has not been reported in online databases or published literature. The clinical presentation of parathyroid lesions and pancreatic nodules in the setting of hypercalcemia should prompt further evaluation of genetic disorders such as MEN1. In this context, it is essential that MEN1 patients be managed with a multidisciplinary approach given the disorder's complexity of diagnosis and treatment. Presentation: Saturday, June 11, 2022 1:18 p.m. - 1:23 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.