6487 Hypercalcemia In Pregnancy Due To An Ectopic Parathyroid Adenoma: A Diagnostic Dilemma

Abstract Disclosure: S.S. Patel: None. M.B. Sharma: None. Introduction: Hypercalcemia is a rare complication of pregnancy, with the most common cause being primary hyperparathyroidism due to a parathyroid adenoma. Ultrasound is the primary modality used for localization, as sestamibi and computed tomography (CT) carry the risk of potential harm to the fetus. We present the case of hypercalcemia in a pregnant female that failed to resolve after two gland parathyroidectomy, necessitating a sestamibi parathyroid scan to localize an ectopic parathyroid adenoma. Case: A 40-year-old pregnant woman at 12 weeks of gestation presented with hypercalcemia, with a corrected calcium level of 12.5 mg/dL (8.7-10.4 mg/dL). She complained of nausea and vomiting but denied any personal or family history of hypercalcemia. Further evaluation revealed primary hyperparathyroidism as the etiology, with Intact PTH of 429.2 pg/mL (18.5-88.0 pg/mL), ionized calcium of 1.45 mmol/L (1.12-1.32 mmol/L), 25-OH vitamin D of 16.4 ng/mL (30-100 ng/mL), phosphorus of 1.3 mg/dL (2.4-5.1 mg/dL), and creatinine of 0.71 mg/dL (0.5-0.8 mg/dL). Notably, her calcium level had been 19.2 mg/dL two weeks earlier during an episode of hyperemesis gravidarum. Hypercalcemia proved relatively resistant to treatment with intravenous hydration and subcutaneous calcitonin. Ultrasound of the neck failed to reveal a parathyroid adenoma. The patient then underwent surgical neck exploration, during which two parathyroid glands were removed, resulting in an intraoperative PTH drop from 440 to 340 pg/mL. Postoperative calcium levels remained elevated at 12.9 mg/dL, prompting the resumption of treatment. Oral sodium and potassium phosphate was added to bind dietary calcium. After an extensive multidisciplinary discussion, a 99mTc-sestamibi parathyroid scan with a lower dose of sestamibi and without CT was recommended. This revealed an ectopic parathyroid adenoma in the anterior mediastinum. Surgical removal of the ectopic parathyroid adenoma in the second trimester finally led to a significant intraoperative PTH drop from 315 to 28 pg/mL. The postoperative course was complicated by hypocalcemia and hypomagnesemia, requiring calcium, vitamin D, and magnesium supplements. These complications resolved over the following days. The patient remained normocalcemic for the remaining pregnancy and delivered a healthy male infant at 34 weeks. Conclusion: Hypercalcemia in pregnancy is associated with fetal and maternal complications, warranting adequate management and close follow-up. The use of 99mTc-sestamibi parathyroid scan is typically not recommended in pregnancy due to concern for fetal harm; however, there are a few studies showing no association with increased birth defects or adverse pregnancy outcomes at low radiotracer doses. Hence, a sestamibi parathyroid scan can be considered during pregnancy to localize an adenoma after a careful review of the benefits versus risks. Presentation: 6/2/2024