Abstracts

RATIONALE: Establishing the efficacy of both pharmacological and non-pharmacological treatments usually requires 12-week, double-blind, placebo-controlled studies. This study examines the effect of continuing vagus nerve stimulation (VNS) among patients who did not respond to VNS during the initial 3 months of treatment.
METHODS: We queried the VNS patient outcome registry for non-responders (patients whose seizures had not decreased by at least by 50%) after 3 months of VNS therapy and for whom 12-month follow-up data were available (constant cohort). We compared changes in seizure frequency, and number and type of antiepileptic drugs (AEDs).
RESULTS: The registry query identified 519 patients, 265 males and 254 females as non-responders. Median age at implantation was 27 years (range, 2 to 79), median age at onset of seizures was 4 years (range, 0 to 53), and median duration of epilepsy was 16.5 years (range, 0.8 to 63). Approximately 12% of the patients lived in residential treatment facilities. Etiology of seizures was known for 41.6% of the patients. The majority of patients (62.4%) had partial seizures with or without secondary generalization. Lennox-Gastaut Syndrome was diagnosed in 12.7% of the patients.
After 3 months of VNS therapy, the median reduction in seizure frequency in this group was 0 and no patients had achieved [gt]=50% seizure reduction. After 12 months of therapy, median reduction of seizure frequency was 28.57%. Seizure reductions [gt]=50% were reported in 37% of the patients.[table]At baseline and after 3 and 12 months of VNS therapy, the most frequently prescribed AEDs were, in order, carbamazepine, lamotrigine, topiramate, valproate, and phenytoin.
CONCLUSIONS: Although the patients in this constant cohort were labeled non-responders after the initial 3 months of VNS, 37% of them achieved reductions in seizure frequency [gt]=50% after 12 months of therapy. The data in this study suggest a cumulative effect of VNS that may require different durations of exposure to VNS in individual patients. Discontinuing VNS before reaching a therapeutic threshold may be premature. Long-term follow-up studies of early non-responders may clarify inter-individual variability of duration of exposure required to achieve therapeutic effect.
Support: Cyberonics, Inc.
Disclosure: Honoraria - Speakers Bureau
VNS Registry Advisory Board, Cyberonics, Inc.