SUN-278 A Conundrum of Calcium: Severe Hypercalcemia Treated With Cinacalcet in the First Trimester of Pregnancy

Abstract K. Champagne: None. R. Minns: None. G.Y. Gandhi: None. Background: Less than 1% of cases of primary hyperparathyroidism occur in pregnancy. The rate of miscarriage increases directly with increasing maternal calcium levels. The most severe neonatal complication is hypocalcemia with tetany. The second trimester is an optimal time for parathyroidectomy due to incomplete fetal organogenesis in the first trimester and the risk of preterm delivery in the third trimester. When a patient presents with symptomatic and severe hypercalcemia in early pregnancy, treatment is fraught with danger due to concerns about the teratogenicity of most calcium-lowering medications. Case: A 33-year-old 9-week pregnant female presented to the hospital with nausea, vomiting, constipation, dehydration, and malaise. Serum calcium (corrected for albumin) was extremely elevated at 19.2 mg/dL. PTH was high at 584 pg/mL, and vitamin D (6.5 ng/mL) and phosphorus (2.0 mg/dL) were low. A 24-hour urine calcium was high at 532 mg, with a fractional calcium excretion consistent with primary hyperparathyroidism at 0.04. Previously, calcium was 11.0 to 12.9 mg/dL, with no record of normal calcium levels. She was not taking any medications or supplements. There was no history of kidney stones, fractures, pituitary or pancreatic pathology, or family history of hypercalcemia. She had previously miscarried a pregnancy at 8 weeks (calcium was elevated at that time to 11.0 mg/dL). Ultrasound showed an echogenic nodule at the lateral aspect of the left thyroid gland, concerning for a parathyroid adenoma. After consultation with obstetrics, surgery, and literature review, cinacalcet 15 mg twice a day was initiated and subsequently increased to 30 mg twice daily, with corrected calcium improving to 13.2 mg/dL before discharge. A large left inferior parathyroid adenoma measuring 2.2 x 1.7 x 1.5 cm and weighing 4 grams was removed at 20 weeks gestation. After surgery, the calcium level normalized after being transiently low. Fetal growth has continued as expected, with no identified abnormalities. C-section is planned at 36-37 weeks. Conclusion: Hyperparathyroidism in pregnancy is rarely diagnosed as symptoms can mimic those of normal pregnancy. We were able to medically manage a patient successfully with cinacalcet as a bridge to surgery without evidence of fetal harm. Cinacalcet is US FDA pregnancy category C. As the calcium-sensing receptor is also located in the placenta, cinacalcet could inhibit transplacental calcium transport and suppress fetal PTH secretion. Acute neonatal hypocalcemia has been reported in gestational cinacalcet cases, but it was transient, and no other adverse events were noted. We advocate for routine antepartum screening for calcium abnormalities, a vital mineral for maternal and fetal health. Cases of hypercalcemia during pregnancy, when discovered, should be reported to help develop evidence-based guidelines for the treatment of this unique population. Sunday, June 2, 2024