Can spikes predict seizure frequency? Results of a pilot study in severe childhood epilepsies treated with vagus nerve stimulation

We evaluated whether spike-rates are useful as an outcome parameter following vagus nerve stimulation (VNS). Spikes/minute and spikebursts/minute were counted in serial electroencephalograms before and after implantation of a vagus nerve stimulator in n = 19 patients with severe childhood epilepsies. In the period of 2 years post VNS, spike-rate and reported seizure frequency were significantly correlated (Spearman's R = 0.61); spikebursts and seizures were correlated with R = 0.74. The response rate, counted after 6 months, was too small to detect differences in responders and non-responders as to spike-reduction. Larger samples and effect sizes are necessary to prove the hypothesis that spike reduction is useful as outcome parameter after VNS or other interventions.