Comparative efficacy of various vitamin D metabolites in the treatment of various types of hypoparathyroidism.

Fourteen patients with pseudohypoparathyroidism, 17 with idiopathic hypoparathyroidism, and 12 with postoperative hypoparathyroidism were treated with vitamin D2, dihydrotachysterol, 1 alpha-hydroxyvitamin D3)1 alpha-OHD3), and 1,25-dihydroxyvitamin D3 for 6-18 months. The optimal maintenance dose or minimum daily dose of 1,25-dihydroxyvitamin D3 to maintain serum calcium at approximately 8.5 mg/100 ml and control all the clinical symptoms was 1.3 +/- 0.16 micrograms/day (mean +/- SE) in pseudohypoparathyroidism, 1.5 +/- 0.18 micrograms/day in idiopathic hypoparathyroidism, and 1.9 +/- 0.50 micrograms/day in postoperative hypoparathyroidism. There was no significant difference in the optimal maintenance dose among the 3 groups. The optimal maintenance dose of 1 alpha-OHD3, however, was 2.0 +/- 0.12 micrograms/day in pseudohypoparathyroidism, significantly lower than that in idiopathic hypoparathyroidism (3.5 +/-0.29 micrograms/day; P less than 0.001) and in postoperative hypoparathyroidism (4.89 +/- 0.54 micrograms/day; P less than 0.001). Significantly lower doses were required in the treatment of idiopathic hypoparathyroidism than in postoperative hypoparathyroidism (P less than 0.05). No significant difference was found in the optimal maintenance dose of dihydrotachysterol and vitamin D2 among the 3 groups. The average pretreatment serum calcium levels and clinical manifestations were indistinguishable among the 3 groups of patients. This suggests that such a difference in the optimal maintenance dose of 1 alpha-OHD3 is ascribed not to the difference in the severity of hypoparathyroidism, but most probably to differences in the pathophysiological processes in pseudohypoparathyroidism and idiopathic or postoperative hypoparathyroidism. The excess parathyroid hormone levels in blood of patients with pseudohypoparathyroidism (and not in other types of hypoparathyroidism) may explain such a difference.