Abstracts

Rationale: Some centers have reported an improvement in seizure control over time with vagus nerve stimulation (VNS). However, most reported studies are prone to methodological biases secondary nonresponder attrition (declining-n) or the imprecision of last visit carried forward analyses. We analyzed the efficacy of VNS over time in a series of 65 consecutive patients with focal and generalized treatment-resistant epilepsy (TRE) who underwent VNS therapy for 10 or more years. Methods: A retrospective review was performed on 436 consecutive patients with TRE who underwent primary VNS implantation by the senior author between 1997 and 2008. Sixty-five patients (29 females/36 males) had undergone VNS therapy for at least 10 years and are the subjects of this report. The mean age at VNS insertion was 30.0 years (range: 6.7 to 73 years) and included 44 adults (? 18 years; 67.7%) and 21 children (32.3%). Seizure frequency and anti-epileptic drug (AED) regimens were recorded prior to VNS and following VNS insertion at 6 months, 1 year, 2 years and every 2 years thereafter. Results: Prior to VNS insertion, the mean weekly seizure frequency was 10.8 24.0 and patients were taking an average of 3 0.6 AEDs. The mean duration of VNS therapy for this group was 10.4 years (range: 10.0 to 11.6 years) and the mean decrease in seizure frequency at last follow-up was 76.3%. The mean percentage seizure reduction at 6 months and years 1, 2, 4, 6, 8 and 10 years was 35.7%, 52.1%, 58.3%, 60.4%, 65.7%, 75.5% and 75.5%, respectively. Seizure frequency was significantly reduced from baseline at each of the recorded intervals (p<0.001) and significant improvements in seizure control were seen between 6 months and 1 year, 1 year and 2 years and years 4 to 6. There was no difference in seizure control between years 2 to 4 years or 6 to 10 years. Four patients had intracranial surgery (callosotomy X 2, brain tumor, cavernoma) after VNS implantation. Two patients underwent device removal and reinsertion after craniotomy and 1 patient had device removal with subsequent increase in seizure frequency. Two patients died from causes unrelated to epilepsy during the follow-up period. There was no significant difference in number of AEDs at any period during follow-up but changes in AED regimens were noted at most interval follow-up visits. Alterations in the device stimulation parameters were common as well, but less frequent than AED changes. Conclusions: Following an initial ramp-up period and accommodation throughout the first year or 2 following VNS implantation, seizure control tended to improve slightly throughout the 10 years of therapy and eventually stabilize. Variation in seizure frequency, however, was common in this population and frequent changes in AED regimens or stimulation parameters were important and possibly synergistic components of seizure control.