Objective: Studies have reported improved seizure control with increased duration of vagus nerve stimulation (VNS) but are prone to methodological biases. We analyzed the efficacy of VNS over time in patients with treatment-resistant epilepsy (TRE) who underwent VNS therapy 10 or more years.
Methods: We retrospectively reviewed 65 consecutive patients (29 females) who underwent VNS therapy ≥ 10 years. The mean age at VNS insertion was 30.0 years. Forty-four adults (≥ 18 years; 67.7%) and 21 children (32.3%) were included. Seizure frequency and antiepileptic 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: The mean duration of VNS therapy for this group was 10.4 years, and the mean decrease in seizure frequency at last follow-up was 76.3%. The mean reduction in seizures 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). There was a trend toward increased AED burden in the latter years of the follow-up period.
Conclusion: Following a "ramp-up" and accommodation period throughout the initial 24 months after VNS implantation, seizure control improved slightly over the subsequent years of therapy and eventually stabilized. Variation in seizure frequency, however, was common, and frequent changes in AED regimens or stimulation parameters were likely an important and possibly synergistic component of seizure control.
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