Electroencephalographic changes in pyridoxine-dependant epilepsy: new observations.

OBJECTIVE: Pyridoxine-dependent epilepsy (PDE) is a rare disease, of which the EEG manifestations are only partially characterised. We report our observations of EEG recordings in four patients with PDE.
MATERIALS AND METHODS: EEG tracings from four patients fulfilling the clinical criteria for PDE were reviewed. Relative to the time of treatment with pyridoxine, EEG recordings were available before treatment in two patients (at ages four and 10 months), immediately after treatment in two patients and during long-term follow-up with treatment in all four patients.
RESULTS: Pre-pyridoxine interictal EEG findings included: diffuse slowing, bilateral independent multifocal epileptiform discharges, generalized bursts of polyspike slow waves and focal or generalized sharp waves. In addition, the EEG was often asymmetrical and included: generalized semi-rhythmic sharp and slow waves, a burst suppression pattern and continuous generalized spike and slow waves. In one patient, who was followed subsequently, a decrease in multifocal spikes and sharp waves and permanent cessation of clinical seizures, within 10 minutes of concurrent reduction of spikes in the pre-existing generalized spike slow wave pattern, was observed immediately after pyridoxine treatment. However, despite the clinical response in this patient we observed persistent generalized burst suppression for four days, and fluctuation of the EEG with diffuse slowing on day four and transient exacerbation of discharges with continuous spike slow waves on day 22. This was followed by intermittent sharp waves at eight and 20 months, mild slowing at 31 months and normal EEG at 43 months. Long-term EEG findings in the other three patients receiving pyridoxine ranged between normal and intermittent multifocal sharp waves.
CONCLUSION: Our data confirm previous observations and provide the following new findings: (1) the presence of burst suppression pattern after cessation of seizures can occur for up to five days after initiation of pyridoxine and should not exclude the diagnosis of PDE, (2) possible fluctuation and even transient worsening of electrographic discharges were observed for up to three weeks after initiation of pyridoxine and (3) the abnormal EEG can persist for up to 43 months before normalizing (range 1-43 months) and in other cases in which it continues to be abnormal it may still improve after increasing the dose of pyridoxine.