Persistent hypoparathyroidism following magnesium repletion in burn-injured children

Children suffering severe burns develop hypocalcemia, magnesium (Mg) deplet ion, hypoparathyroidism, and renal resistance to parathyroid hormone (PTH) infusion. We hypothesized that Mg depletion accounted for both the hypopara thyroidism and the renal resistance to PTH, and that Mg repletion would imp rove both. Due to a lack of PTH for infusion, we studied only the effect of Mg repletion on the relationship between ionized Ca (iCa) and PTH in the s erum of 14 sequentially recruited children burned greater than or equal to 40% total body surface area. All received a urinary ME retention test a med ian of 20 days post burn (range 8-137 days). Seven (50%) of the children re mained Mg depleted, which was not attributable to burn size or to time from burn to study. Combined enteral and parenteral Mg intakes were not differe nt between the depleted and repleted groups, 12.2+/-4.4 (SD) mg/kg per day and 14.2+/-6.2 mg/kg per day, respectively, Both groups had low intact PTH levels in relation to serum iCa concentration, indicating persistent hypopa rathyroidism, We conclude that Mg depletion is not the chief cause of hypop arathyroidism following thermal injury and we postulate that the persistent hypoparathyroidism is consistent with a reduced set-point for Ca suppressi on of PTH secretion.