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Abstract
Intermittent calcitriol therapy is commonly used to treat secondary hyperparathyroidism
in patients undergoing regular dialysis, but there is little available information
about the histologic response of bone to this form of therapy. Accordingly, 14 children
and adolescents with biopsy-proven secondary hyperparathyroidism were treated with
intermittent oral or intraperitoneal doses of calcitriol for 12 months. Biochemical
indices of mineral metabolism including serum intact PTH levels were measured monthly
throughout the study, and bone biopsies were repeated at the end of treatment. Before
treatment, 11 patients had osteitis fibrosa and three had mild lesions of secondary
hyperparathyroidism. Histologic improvement was seen in 12 of 14 patients, and osteitis
fibrosa resolved in 10 of 11 cases. Bone formation decreased in all patients during
intermittent calcitriol therapy, falling from 861 +/- 380 to 150 +/- 170 microns2/mm2/day,
P < 0.001. Bone formation decreased to normal in six patients, but six patients developed
adynamic lesions of bone with subnormal bone formation rates. Serum PTH and alkaline
phosphatase levels declined in those who developed adynamic bone, but values remained
elevated in patients with normal rates of bone formation at follow-up evaluation.
Neither the mean dose of calcitriol nor the average dose per kilogram body weight
differed in patients with adynamic lesions. Thus, adynamic renal osteodystrophy develops
in a substantial number of patients during intermittent calcitriol therapy. Although
declining serum PTH and alkaline phosphatase levels suggest the development of the
adynamic lesion, bone formation decreases in some patients despite persistently high
serum PTH levels. Calcitriol may directly suppress osteoblastic activity in patients
with secondary hyperparathyroidism when given in large doses to patients undergoing
peritoneal dialysis.