Iatrogenic Hypercalcemia and Management of Postoperative Hypoparathyroidism During Lactation

Introduction : We present a case of postoperative hypoparathyroidism following surgery for thyroid cancer in a lactating woman. Challenges involving the management of hypoparathyroidism while lactating are discussed.

Case Description : A 32-year-old female was evaluated for a left-sided neck mass during her third trimester of pregnancy. CT scan revealed pathologic lymphadenopathy and a thyroid mass. FNA showed metastatic papillary thyroid cancer. She underwent total thyroidectomy and lateral and central neck dissection five weeks postpartum while breastfeeding. Parathyroid glands were identified intraoperatively, and pathology did not identify parathyroid tissue. PTH decreased from 38 pg/mL (ref 15-65 pg/mL) preoperatively to 9 pg/mL intraoperatively. Immediately postoperatively she developed symptomatic hypocalcemia. Ionized calcium (iCal) was 3.6 mg/dL (ref 4.4-5.4 mg/dL). She was given 2 grams IV calcium gluconate with improvement in symptoms. Oral supplementation with calcium carbonate 1 gram 4 times daily and calcitriol 0.5 mcg twice daily was started. No further episodes of hypocalcemia occurred. She was discharged on Levothyroxine 125 mcg daily, calcitriol 0.5 mcg daily and calcium carbonate 1 gram 3 times daily.
　
On postoperative day 7, labs revealed calcium 12.4 mg/dL (ref 8.4-10.5 mg/dL), iCal 6.1 mg/dL, and Vitamin D 25, OH 36.5 ng/mL (ref 32–100 ng/mL). She endorsed fatigue and was continuing to breastfeed. Calcium supplementation and calcitriol were discontinued. One month later calcium was 9.2 mg/dL with PTH 38 pg/mL.

Discussion : Transient postoperative hypoparathyroidism is a common phenomenon after thyroidectomy, occurring in up to 50% of patients. Most patients recover parathyroid function within one month. In lactating women special consideration to calcium levels is needed due to the risk of iatrogenic hypercalcemia. This is because of the physiologic changes present to meet increased calcium requirements during lactation. Parathyroid hormone (PTH) levels do not increase significantly during pregnancy or lactation. Instead, increased parathyroid hormone related protein (PTHrP) is present in maternal circulation. During lactation, increased calcium needs are met via PTHrP mediated bone demineralization and a low estrogen state. As PTH is not needed for calcium mobilization during lactation, one must be cautious and proactive with adjusting both calcium supplementation and calcitriol use to prevent hypercalcemia. This makes postoperative hypocalcemia more challenging to manage in lactating patients.