Long-term outcome in pyridoxine-responsive infantile epilepsy

Dose regimens of pyridoxine (vitamin B6) for treatment of infantile spasms have varied from 200 mg/d to 300 mg/kg/d. Only two long-term outcome studies of the treated patients are available.

We asked all pediatric neurologists treating pediatric epilepsy in Finland if they had seen patients with pyridoxine-responsive infantile epilepsy. Five children with infantile spasms and hypsarrhythmia and one with focal epilepsy were reported as pyridoxine responders. Data on clinical presentation and outcome were collected from patient charts.

All B6 responders had un-known aetiology. Two patients were studied for pyridoxal 5'-phosphate oxidase (PNPO) deficiency and showed negative results. Ages at seizure onset ranged from 4 to 7 months. The maintenance dose of oral pyridoxine was 150 mg/day. Response occurred within 1-to 14 days (mean 5 days). Two patients were treated with concomitant antiepileptic drugs. Duration of pyridoxine therapy varied from 6 weeks to 4 years (mean 26 months). Four patients had later seizure recurrence: one at 15 months with motor seizures (stopped by valproate), another two in adolescence with focal epilepsy and one at 20 years with unclassified epilepsy. Intelligence was normal in five patients and one had a mild mental deficiency. Follow-up ranged from 8.5 to 24 years.

Rare patients with infantile epilepsy but not pyridoxine dependency may respond to smaller doses of pyridoxine than reported before. Long-term cognitive outcome appears to be good but late seizure recurrence (in adolescence or in adulthood) occur. So far it is unknown if the response was determined by genetic traits or disease-related factors.