Abstracts

This is a Late Breaking abstract

Rationale: Because complete seizure-freedom is rare in drug-resistant epilepsy (DRE), efficacy of DRE treatments is typically assessed by quantifying relative seizure frequency reduction and the fraction of patients experiencing 50% or greater reduction in seizure frequency defined as the responder rate. However, recent data suggests that the amount of consecutive seizure-free days is a critical determinant of quality of life in patients with DRE. Although vagus nerve stimulation (VNS) is an established therapy for DRE and in clinical use for over 25 years, the fraction of patients with VNS experiencing prolonged periods of seizure freedom has yet to be assessed on a large scale

Methods: We retrospectively analysed the fraction of patients in the Japanese VNS Post Market Registry experiencing at least one year of seizure freedom from three separate seizure counts: all seizures, focal seizures, and generalized tonic-clonic seizures. Patients in this registry (UMIN ID: UMIN000014728), which included 52 sites in Japan, underwent VNS implantation between July 2010 and December 2012.

Results: After 36 months of treatment with VNS the cumulative fraction of patients experiencing at least one year of complete seizure-freedom was 11% (38/356) with an average duration of seizure freedom of 19.4 months. Of the 225 patients who experienced focal seizures prior to VNS implantation, 57 (25%) experienced at least one year of freedom from focal seizures while receiving VNS with an average duration of seizure freedom from focal seizures of 24.8 months. Higher cumulative rates of freedom from bilateral tonic clonic seizures (BTCS) were observed throughout the 36-month follow-up period: of the 184 patients who experienced BTCS prior to VNS implantation, 101 (55%) experienced at least one year without any BTCS with an average duration of BTCS-free periods of 28.9 months. When excluding the 25 patients who experienced BTCS prior to VNS, but not in the 3-month baseline period before implantation, 1-year seizure-freedom from BTCS was experienced by 49% of patients (78/159) with a 79% responder rate from BTCS at the 36-month visit.

Conclusions: Although complete seizure freedom is rare in patients undergoing VNS Therapy (11%), in this analysis we found that approximately half of patients who experienced BTCS prior to VNS experienced prolonged periods of freedom from BTCS after receiving VNS Therapy. This is of interest as many DRE patients and/or their care-givers consider BTCS to be their most debilitating seizure type, and BTCS have been shown to have a high association with head-trauma, other seizure-related injuries, and are the main risk factor for sudden unexpected death in epilepsy (SUDEP). 

Funding: This study was funded by LivaNova PLC.