Does response to vagus nerve stimulation for drug-resistant epilepsy differ in patients with and without Lennox-Gastaut syndrome?

Abstract

Literature on outcomes of patients with Lennox-Gastaut syndrome (LGS) receiving adjunctive vagus nerve stimulation (VNS) lacks information on seizure types and the time course of therapeutic effects. We have therefore performed what is to our knowledge the largest and most in-depth analysis of the effectiveness of VNS in LGS patients paying special attention to the impact of VNS Therapy on individual seizure types. The VNS Therapy Outcomes Registry includes over 7000 patients. A propensity score matching method was employed to match patients with LGS to non-LGS patients with drug-resistant epilepsy (DRE). Overall seizure frequencies were assessed prior to implantation and at 3-, 6-, 12-, 18-, and 24-month follow-ups to derive the main study outcomes: response rates and time to first response. A total of 564 LGS patients with sufficient data were identified in the registry and matched 2:1 to 1128 non-LGS patients. Responder rates at 24 months were 57.5% in the LGS group and 61.5% in the non-LGS group. Median seizure frequency reduction at 24 months was 64.3% versus 66.7% in the LGS versus non-LGS group, respectively. In both groups, VNS was most effective at reducing focal aware seizures, "other" seizures, generalized-onset non-motor seizures, and drop attacks with relative reduction rates for these seizure types at 24 months exceeding 90% in both groups. Time-to-first response did not differ between the groups; however, there was a significantly higher proportion of patients who regressed from bilateral tonic-clonic (BTC) seizure response in the LGS group versus the non-LGS group at 24 months: 22.4% versus 6.7%; p=.015. Although limited by its retrospective design, the study shows that the effectiveness of VNS is comparable in DRE patients with and without LGS; however, LGS patients may be more prone to fluctuating control of BTCs.