Parathyroid hormone-related peptide induced hypercalcemia of pregnancy due to mammary hyperplasia

Maternal Parathyroid Hormone-related Protein (PTHrP) is involved in the placental transport of calcium. Autonomous overproduction of PTHrP is a rare cause of hypercalcemia in pregnancy. Prior cases of PTHrP-induced hypercalcemia in pregnancy have been managed with either dopamine agonists, fetal delivery, termination of pregnancy, or mastectomy. However, PTHrP level normalization following mastectomy has not previously been documented. Herein, we present a 39-year-old female hospitalized at 19 weeks of gestation for acute encephalopathy due to PTHrP induced hypercalcemic crisis (calcium 15.8 mg/dL, PTHrp 46.5 pmol/L [normal 0-3.4]). Mammary hyperplasia resulting in gigantomastia significantly impaired her ability to ambulate and perform activities of daily living. She remained hypercalcemic during hospitalization despite aggressive hydration, calcitonin, and 2 weeks of dopamine agonist treatment. Bisphosphonate therapy was not administered due to pregnancy and potential effects on the fetus. Our patient underwent bilateral mastectomy along with excision of a large axillary mass. The pathology of all three specimens revealed mammary stromal hyperplasia. PTHrP was undetectable on post-op day 2 and calcium normalized by post-op day 3. At discharge, she was able to ambulate independently. To our knowledge, this is the first reported case of PTHrP induced hypercalcemia related to gigantomastia, documenting resolution of hypercalcemia, and PTHrP levels following mastectomy. Mastectomy is a potential option in the second trimester for pregnant patients with PTHrP induced severe hypercalcemia due to gigantomastia, refractory to treatment with dopamine agonist therapy.