[Hypomagnesemia-induced hypocalcemia: functional hypoparathyroidism, parathyroid hormone- and vitamin D-resistant]

In four patients with severe hypomagnesemia, hypocalcemia, and functional hypoparathyroidism (three patients with shortened bowel, one with alcoholism), sequential measurements of parameters of calcium metabolism were performed before and during intravenous administration of magnesium. Parathyroid hormone was immeasurably or inadequately low in all patients before magnesium injection, but rapidly rose to elevated values thereafter. Even without calcium supplements, serum calcium rose to normal levels within 2-5 days, although 1,25(OH)2-Vitamin D levels did not rise significantly. In the patient with alcoholism, hypophosphatemia developed during the first days after admission; the rise of serum calcium preceded the elevation of cyclic adenosine monophosphate in urine. A transient rise of urinary calcium was observed in two patients after initiation of magnesium therapy, with a subsequent fall to subnormal levels in spite of normal serum calcium concentrations. The findings were considered to be due to partial parathyroid hormone resistance during the phase of magnesium replenishment.