SAT195 A Curious Case Of Severe Reversible PTH-mediated Hypercalcemia Of Pregnancy

Disclosure: I. Albanese: None. N. Nicolas: None. S.S. Wing: Grant Recipient; Self; Pfizer Global R&D. Other; Self; Almac Discovery (Independent Contractor). E. Mitmaker: None. L. Vautour: None. Background: Primary hyperparathyroidism is rarely diagnosed in pregnancy as symptoms may overlap with those of pregnancy and biochemical diagnosis may be masked by physiologic changes in calcium homeostasis. Hyperparathyroidism in pregnancy is associated with increased maternal and fetal complications. While mild disease is treated conservatively, moderate to severe disease is generally treated surgically in the second trimester. Safe pharmacotherapy options are limited in pregnancy. Case: A 35-year-old woman G3P1 at 10 weeks presented to our institution with polyuria, bone pain and weakness with labs demonstrating severe hypercalcemia (Calcium total: 3.82mmol/L (normal: 2.12-2.62); PTHi: 12pmol/L (normal: 1.5-9.3)). PTHrP was suppressed. She had a prior history of PTH-mediated hypercalcemia in her first pregnancy. She previously underwent three exploratory surgeries in which only three parathyroid glands were found and removed. The hyperparathyroidism and hypercalcemia persisted post-operatively thus she also required intravenous fluids, calcitonin and cinacalcet. The pregnancy was otherwise uncomplicated. Post-partum, she developed hypoparathyroidism and hypocalcemia. Throughout this current pregnancy, multiple imaging modalities were used (ultrasound, MRI and parathyroid sestamibi), none of which were unable to localize any hyperfunctioning parathyroid tissue. Thus, management was limited to medical therapy. Despite aggressive hydration, calcitonin and cinacalcet, total calcium and PTH levels consistently rose reaching peaks of 4.06mmol/L and 45.4pmol/L, respectively. Given hypercalcemia severity and associated neurological symptoms, she was also given bisphosphonates (pamidronate 60mg and zoledronic acid 4mg). She underwent C-section at 25+3 weeks due to fetal decelerations and placental insufficiency. She again developed hypoparathyroidism and hypocalcemia 1-week post-partum. Genetic testing was negative for any causes of hyperparathyroidism. Discussion: This is a unique case of severe PTH-mediated hypercalcemia in that the exact mechanism is unknown but appears to be pregnancy-mediated and reversible such that it only occurs in pregnancy with subsequent hypoparathyroidism post-partum. Investigations to better elucidate the mechanism of this are ongoing. Presentation: Saturday, June 17, 2023