Effect of Long‐term Vitamin D2 Treatment on Bone Morphometry and Biochemical Values in Anticonvulsant Osteomalacia

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Abstract
Quantitative morphometric analyses of iliac crest biopsies from 20 epileptic patients receiving chronic anticonvulsant therapy were performed before and after 4-8 mo. of vitamin D2 treatment with 9000 U/day. Biochemical quantities, including serum 25-hydroxycholecalciferol (25-HCC) and serum parathyroid hormone (iPTH) were measured. The anticonvulsant osteomalacia found in the initial bone biopsies was characterized by an increased amount of unmineralized bone, an increased bone resorption and an increased bone mineralization and bone formation. Bone resorption and bone formation were probably equally increased since the amount of cancellous bone was normal. Except for a slight increase in osteoid-covered surfaces and osteoclastic resorption surfaces, the bone changes were normalized after vitamin D2 treatment, leading to a mean serum level of 25-HCC 2.4 times above normal. Serum iPTH was normal before and unchanged during D2 therapy. The urinary Ca excretion remained decreased. The investigation characterizes anticonvulsant osteomalacia as a specific bone disease different from that of vitamin D deficiency but induced by abnormalities in vitamin D metabolism or in the effects of vitamin D metabolites on receptor cells.