Plasma and Erythrocyte Magnesium in Thyroid Disease

Abstract
Serial determinations of plasma and erythrocyte magnesium concentrations were made before and during therapy in 13 hyperthryoid and 12 hypothyroid patients. Plasma magnesium concentrations were initially subnormal in 7 hyper-thyroid patients and returned to normal as a response to antithyroid therapy became manifest. In 6 normomagnesemic hyperthyroid patients, plasma magnesium concentrations also tended to increase with therapy. Six hypothyroid patients had supranormal plasma magnesium concentrations prior to therapy. These returned to normal with treatment in 5 patients, but 1 subject showed a persistent elevation of the plasma magnesium concentration despite a satisfactory response to therapy. A decrease in plasma magnesium concentrations also occurred in the 6 normomagnesemic hypothyroid patients. Pretreatment erythrocyte magnesium concentrations were subnormal in 6 hyperthryoid and 1 hypothyroid patient. The response of erythrocyte magnesium concentrations to therapy was unpredictable, and increased, decreased or remained unchanged without relation to thyroid status or plasma magnesium concentrations. Evidence suggests that these alterations in extracellular magnesium concentrations in thyroid disease result either from a defect in magnesium balance or in magnesium distribution. Since the erythrocyte magnesium concentration appears to be a poor indicator of body magnesium in thyroid disease, resolution of this problem must await the development of precise measurements of total and available tissue magnesium concentrations.