Clinical Efficacy of VNS Therapy

A consensus of publishedstudies based on a mixed sample of individuals with and without ID has demonstrated the benefits of VNS Therapy.13 • 16 26 Initially pilot studies showed the short-term benefit of VNS Therapy in refractory epilepsy.1123 •27,28

Uthman and colleagues28 reported findings from two single-blind studies (designated EO1 and EO2) that treated 14 patients (no information given about IQ status). The mean reduction in seizure frequency after 14 to 35 months was 46.6%. Five (35.7%) individuals had a reduction of at least 50% seizure frequency. Vonck and colleagues26 prospectively assessed 131 patients treated with VNS Therapy. The mean age of the patients was 32 years, and the mean duration of refractory epilepsy was 22 years. The mean reduction in monthly seizure frequency was 55%. Seven percent were free of seizures, 50% had a seizure frequency reduction of more than 50%, and 21% were nonresponders.

A number of randomized controlled studies have been reported,29-31 confirming the findings from the earlier studies, which were more susceptible to investigator bias. The Vagus Nerve Stimulation Study Group29 performed a multicenter RCT in 114 patients randomized to receive 14 weeks of high-level or low-level stimulation using a blinded parallel study design. No information was given regarding ID status. Mean reduction in seizure frequency was seen in both groups (24.5% for "high" group and 6.1% for "2ow" group. Thirty-one percent of the "high" group had a reduction of 50% or more seizure frequency.

The long-term benefits of VNS Therapy have been reported.32-35 Morris and col-leagues33 evaluated the results of long-term open-label treatment of 440 patients with refractory epilepsy with VNS Therapy from five clinical trials. No information was given regarding ID status. A 50% seizure reduction occurred in 36.8% of patients at one year, in 43.2% at two years, and 42.7% at three years. Alexopoulos and colleagues35 reviewed VNS data for 46 patients. The median age at implantation was 12.1 (range 2.3-17.9) years and the median duration of epilepsy 8.0 (1.916.9) years. Seizure frequency reduction in the range of 60% was observed at one, two, and three years post VNS. Overall long-term studies suggest that the efficacy of VNS Therapy is maintained over time.

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