PSAT215 Hypercalcemic Crisis Complicating a First Trimester Pregnancy Caused by a Giant Parathyroid Adenoma Masquerading as a Thyroid Nodule

BACKGROUND: Primary hyperparathyroidism (PHP) during pregnancy is rare with a reported incidence of 1%, although the true incidence is unknown. It is associated with increased morbidity and mortality for both mother and fetus. Most reported cases of PHP during pregnancy are due to small adenomas causing mild hyperparathyroidism. Surgical management is recommended if the calcium level is >11mg/dL (2.75mmol/L) or the patient has symptomatic hypercalcemia. It is generally recommended that surgery be performed in the second trimester due to the risk of miscarriage in the first trimester, and preterm labor in the third trimester. CASE: A 29-year-old woman presented to our emergency department at 10 weeks’ gestation with nausea and vomiting. She also reported constipation and fatigue. On examination, she was euvolemic, awake and alert, with no neurological symptoms or signs. The suspected diagnosis was hyperemesis gravidarum until her laboratory evaluation revealed marked hypercalcemia [15.6mg/d (3.9mmol/L)]. Further labs revealed hypophosphatemia [1.2mg/dL (0.39mmol/L)], hypokalemia [3.3mEq/L], hypomagnesemia [1.4mEq/L], low 25-hydroxy vitamin D [16.2ng/mL (40.44pmol/L)], and elevated intact parathyroid hormone (iPTH) [573pg/mL], 1,25-dihydroxy vitamin D [251.1pg/mL (626.75pmol/L)], and 24 hour urinary calcium [448mg/24 hours (11.2mmol/24 hours]. On cardiac evaluation, her QTc was normal. The patient was given intravenous hydration with normal saline, which reduced the calcium to 13.6mg/dL (3.4mmol/L) after 48 hours. She remained symptomatic and severely hypercalcemic, so calcitonin 4 IU/kg every 12 hours was added, while a neck ultrasound was performed to localize the parathyroid adenoma. Her calcium level decreased to 10.7mg/dL (2.7mmol/L) after calcitonin, but rapidly rebounded to 13.3mg/dL (3.3mmol/L) along with hypophosphatemia and hypokalemia. Intravenous potassium phosphate was initiated and her calcium decreased to 11.8mg/dL (2.95mmol/L). The neck ultrasound did not identify a parathyroid adenoma, but identified a 2.5×1.5×3.3 cm right mixed cystic/ solid thyroid nodule. An MRI of the neck revealed two right thyroid nodules. The decision was made to perform a neck dissection given the persistent severe hypercalcemia after a multidisciplinary team evaluation, and extensive discussion with the patient. The surgical exploration of the right neck identified a giant parathyroid adenoma that weighed 11.3g. The intraoperative PTH levels reduced from 804pg/mL to 60.7pg/mL. Her calcium normalized immediately postoperatively and she was discharged home without complication. At the time of last follow up, she was 18 weeks’ gestation and a fetal ultrasound was normal. DISCUSSION: This case had three unusual features: PHP causing severe hypercalcemia during pregnancy; a giant parathyroid adenoma; and parathyroid adenoma masquerading as a thyroid nodule on imaging. This case highlights the importance of a multidisciplinary team approach in optimizing the care of such complicated patients, along with the need for definitive surgical intervention. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.