Renal magnesium wasting and functional hypoparathyroidism: a diagnostic and therapeutic challenge in hypocalcemia.

INTRODUCTION

Symptomatic hypocalcemia and hypomagnesemia are life-threatening emergencies. Acute diagnostic and therapeutic maneuvers are well known, but underlying etiologies and the long-term therapeutic choices are not.

METHODS

A 38-year-old woman who was found to have metastatic malignant melanoma during post-iodide 131 treatment uptake and whole-body scanning for treatment of differentiated thyroid cancer presented to an emergency department after the third round of platinum-based chemotherapy with severe muscle cramping. She was found to have profound hypocalcemia that was treated. The next day, her symptoms returned, and severe hypomagnesemia was found in a visit with her oncologist.

RESULTS

Blood and urine tests revealed severe renal magnesium wasting and inappropriately normal intact parathyroid hormone given her severe hypocalcemia. All electrolyte abnormalities resolved with intravenous magnesium administration over 2 days.

DISCUSSION: Severe renal magnesium wasting can cause concurrent functional hypoparathyroidism. Recognition of concurrent hypomagnesemia is essential in the laboratory workup of hypocalcemia.