Effect of vitamin D 3 (cholecalciferol) in anticonvulsant osteomalacia

Abstract

Two patients who had been receiving anticonvulsant drugs for 12 and 18 years respectively are described. The findings of myopathy, bone pain and fractures combined with hypophosphatemia, a raised alkaline phosphatase and generalised aminoaciduria were consistent with a diagnosis of osteomalacia. Undecalcified bone sections confirmed the presence of severe osteomalacia. The finding of a low circulating level of 25-OH vitamin D combined with a dramatic clinical, biochemical and histological response to a single dose of intravenous vitamin D 3 (cholecalciferol), 1 mg, suggested a state of vitamin D deficiency. Dietary intake of vitamin D was normal and intestinal malabsorption excluded in both patients. Absorption of 25-OH vitamin D 3, studied in one patient, was normal. These observations support the view that in anticonvulsant osteomalacia, the state of vitamin D deficiency is related to deranged metabolism of the vitamin induced by anticonvulsant drugs.