Abstracts

Rationale: Only a few studies are available reporting long term efficacy of vagus nerve stimulation (VNS). We present data on efficacy of VNS in adult patients treated for 5 years. Methods: 58 adult patients underwent VNS implant for medically intractable epilepsy at the University of Michigan between January, 1999, and May, 2002. Patients with consistent follow up for 5 years post implant were included in the retrospective analysis. 15 patients were excluded for inadequate follow up due to VNS turned off (1), VNS explanted due to discomfort (2), VNS explanted due to infection (2), lost to follow up (8), and death (2). One patient was re-implanted post infection but did not have 5 years of treatment at the time of this data collection. All patients had anticonvulsant therapy during treatment with VNS and all patients had medication adjustments to some degree during the 5 years. 16 patients had VNS generator replacements during the 5 years due to concerns about end of battery life.Results: The 43 patients ranged in age from 15 to 57 at implant. 14 (32%) were female. 30 had focal epilepsy (FE), 2 had primary generalized epilepsy (PGE), and 11 had symptomatic generalized epilepsy (SGE). After 6 months of VNS, 22 patients (16 FE, 6 SGE) were nonresponders, 8 (5FE, 1SGE, 2PGE) had 25% seizure reduction, 10 (6FE, 4SGE) had 50%, and 3 (FE) had 75%. At one year of VNS, 15 patients (11 FE, 5 SGE) were nonresponders, 7 (4FE, 2 SGE, 1PGE) had 25 % seizure reduction, 14 (9 FE, 4 SGE, 1 PGE) had 50%, 5(FE) had 75% and 1 (FE) had 100%. At 5 years of VNS, 13 patients (8FE, 4 SGE, 1 PGE) were nonresponders, 3 (1 FE, 2 SGE) had 25% seizure reduction, 16 (12 FE, 4 SGE) had 50%, 8 (7FE, 1 SGE) had 75%, and 3 (2 FE, 1 PGE) had 100%. Of the 22 nonresponders at 6 months, 6 patients (5 FE, 1 SGE) demonstrated efficacy at one year, 5 (3 FE, 2 SGE) at 2 years, and 2 (FE) at 3 years of treatment. Among early responders, (efficacy at 6 months of VNS), 8 patients(5 FE, 2 SGE, 1 PGE) improved further during the 5 years. 9 (6 FE, 3 SGE) early responders maintained the same efficacy over the 5 years. There were 9 patients (6 FE, 3 SGE) who were nonresponders for the entire 5 years. 4 patients (2 FE, 1 SGE, 1 PGE) had some efficacy in the first years that declined during the 5 year interval. Conclusions: These data show that a majority of patients achieved efficacy from VNS during 5 years of treatment. Many nonresponders at 6 months improved at one year and two years of treatment, and only a couple of patients improved after that. Many early responders (efficacy at 6 months) maintained the same rate of efficacy, or had improved efficacy over the 5 years. Only a couple of patients achieved complete seizure control. A few patients were nonresponders or demonstrated declining efficacy over 5 years. These data show that patients should have at least 2 years of VNS before determining the effectiveness of treatment.