Anticonvulsant osteomalacia in epileptic outpatients

The occurrence of anticonvulsant osteomalacia was studied in 23 epileptic outpatients, and in age and sex matched controls. Hypocalcaemia was observed in 10, hypophosphataemia in 1, and increased serum alkaline phosphatase in 8 of the patients. The serum 25-hydroxyvitamin D concentration was significantly lower In the patients than in the controls, but no difference was found in the serum 24,25-dihydroxyvitamin D concentration between the patients and the controls. There was no difference in bone mineral density between the patients and the healthy controls. In the histomorphometric study, no differences were found in the amount of trabecular bone or osteoid between the patients and the controls, but the patients had a slightly more extensive trabecular resorption surfaces. Histological osteomalacia was found in two of the 23 cases (9%). We conclude that epileptic outpatients on long-term anticonvulsant therapy have vitamin D deficiency and may develop osteomalacia.