Vagus nerve stimulation for 1 year in 269 patients on unchanged antiepileptic drugs

PURPOSE To study, in patients on unchanged antiepileptic drugs (AEDs): (1) seizure rates after 3 and 12 months of vagus nerve stimulation (VNS); (2) effects of VNS parameters; (3) patient characteristics versus VNS responsiveness. METHODS We located in the VNS registry 269 patients treated for 1 year with no changes in AEDs. Seizure rates were calculated at 3 and 12 months. We analyzed: (1) 3 months versus 12 months seizure rates; (2) effects of changing duty cycles between 3 and 12 months; (3) effects of output current; (4) seizure rate changes associated with patient characteristics. RESULTS Seizure rates improved between 3 months (median = -45%) and 12 months (median = -58%) (P < 0.0001). There were no differences between patients who stayed on standard or rapid cycling, or changed from standard to rapid. Stimulation parameters did not affect seizure rates. VNS responsiveness was associated with older age (P = 0.016), longer duration epilepsy (P = 0.033), and syndromes other than Lennox-Gastaut (P = 0.003). CONCLUSIONS This was an analysis of treatment outcomes, not a prospective clinical trial. Nonetheless, our results suggest: (1) seizure rates decline with increasing VNS duration; (2) this decline occurs without AED changes; (3) this decline is not due to changes in stimulation parameters; (4) patient characteristics predictive of VNS responsiveness remain elusive.