ODP076 A Unique Case of Iatrogenic Hypermagnesemia Induced Symptomatic Hypocalcemia
Authors: Singles Andrew , Sekar Vijaykumar , Rauf Mohammad Uzair Abdul , Shaik Shamsuddin 
Published: November 2022

Abstract

Introduction
Magnesium plays a role in production, release, and end-organ responsiveness of parathyroid hormone (PTH) and calcium homeostasis. Hypomagnesemia has been well documented to cause hypocalcemia by impaired secretion of PTH or PTH resistance. Iatrogenic hypermagnesemia in pregnant patients receiving intravenous magnesium for suppression of premature labor and pre-eclampsia is an uncommon cause of hypocalcemia. We are reporting a case of symptomatic hypocalcemia caused by iatrogenic hypermagnesemia in post-partum mother, who had high PTH in contrast to previous case reports. CaseA 28-year-old G4P1122 female, postpartum day 16 was admitted for headache, slurred speech, and vomiting. She was found to have elevated blood pressures and was started on IV magnesium for postpartum preeclampsia. On her first day, she received a 4g bolus of magnesium sulfate followed by 2g as maintenance for seizure prophylaxis. The following morning, the patient awoke complaining of numbness/tingling in both arms and twitching in her face and eyelids. Later that day, she had developed bilateral spontaneous carpopedal spasm as well. Labs drawn at that time revealed ionized calcium 0.78mmol/L (1.18-1.32 mmol/L), corrected calcium 7.42mg/dL (8.5-10.1), vitamin D 25-OH 45ng/mL (30-100), PTH 149.1pg/mL (18.5-88), phosphorus 2.9mg/dL (2.3-4.6), GFR116mL/min (&gt;60) and magnesium 3.5mg/dL (1.4-2.2). Patient was started on IV calcium gluconate infusion along with calcium carbonate 1g QID and vitamin D3 5000 units daily. By the evening of the second day, patient's carpopedal spasm and paresthesia completely resolved. Repeat labs demonstrated improved ionized calcium of 1.17mmol/L (1.18-1.32), corrected calcium of 9.78mg/dL (8.5-10.1), and magnesium of 1.5mg/dL (1.4-2.2). Patient was discharged on calcium carbonate 1g TID and Vitamin D3 5000 units daily. Patient self-discontinued calcium and vitamin D supplementation a week after discharge. Repeat labs one week later showed normal corrected calcium, magnesium, and PTH levels.

Conclusion
Our patient developed transient, symptomatic hypocalcemia with elevated PTH secondary to iatrogenic hypermagnesemia, which improved with intravenous calcium. Hypomagnesemia is a known cause of hypocalcemia, but hypermagnesemia is a significantly less recognized etiology. Hypermagnesemia can cause low PTH due to activation of calcium sensing receptors resulting in inhibition of PTH secretion. Hypermagnesemia can also blunt the peripheral effect of PTH and promote hypercalciuria. Previous studies showed PTH can peak by the end of magnesium infusion but still result in hypocalcemia, although this is an uncommon clinical presentation. Our case highlights this aspect of elevated PTH after the completion of IV Magnesium infusion but still unable to correct hypocalcemia due to PTH resistance from hypermagnesemia. This calls attention to another underrecognized sequalae of hypermagnesemia: blunting of peripheral tissues response to PTH. Clinicians should be aware of development of hypocalcemia with both hypo- and hypermagnesemia as well as the underlying pathophysiology.
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