Vagus Nerve Stimulation In The Treatment Of Drug-resistant Epilepsy

ObjectiveTo investigate the clinical efficacy and side-effect of vagus nerve stimulation (VNS) in the treatment of drug-resistant epilepsy.MethodsAccording to the inclusion and exclusion criteria,18 drug-resistant epileptic patients were selected among the epileptic patients who visited The Second Affiliated Hospital of Zhejiang University from 1/1/2014-12/31/2014, and the clinical data, brain MRI and quantitative EEG of these patients were collected. Under general anesthesia, vagus nerve stimulation device was implanted in every patient. Two weeks after activation of the device, we adjusted the stimulation parameters according to the individual variation. All the patients were asked to record every seizure by keeping a diary until 1 year after surgery. EEG examination in accordance with the international 10/20 system with 16 tubular electrodes, collected brain electric signals without artifact which could represent background of brain activity, sampling 30 seconds. Using fast Fourier transformation, we analyzed the absolute and relative power quantitatively of 8 wave (0.5～3.5 Hz),θ wave (4.0～7.5 Hz), a wave (8～13 Hz), β wave (14～30 Hz) in 16 brain regions and calculated W value which equaled to (δ+θ)/(α+β). Epileptic seizures were counted with statistics, quantitative EEG was repeated in every patient. Paired t test was used for the comparison within the patients before and after the surgery, a p value less than 0.05 suggested statistically significant differences.ResultsAll 18 drug-resistant epileptic patients were focal epilepsy, the median age of patients was 19 (11,25) years old, the median age of onset age was 3 (1,12) years old, the median duration of disease was 13 (7,20) years. Among all patients,9 (50%) patients were men, and 9 (50%) patients were women, with 7 (38.9%) children, 11(61.1%) adults. As for the past medical history,1 (5.5%) patient had cerebral trauma, 1 (5.5%) patient had encephalitis,1 (5.5%) patient had a history of dystocia, and 1 (5.5%) patient had a corpus callosum incision surgery. Before VNS surgery, mean epileptic seizure frequency was 88.0±146.2 per month. At the 6th month after surgery, mean epileptic seizure frequency was decreased to 34.1±51.9 per month with significant difference (P<0.05). At the 12th month, mean epileptic seizure frequency was decreased to 25.9±39.2 per month with significant difference (P<0.05). When modified Engel grading scores were used to assess the effectiveness of VNS, the results were that none reached grade Ⅰ,5 (27.8%) patients reached grade Ⅱ,9 (50.0%) patients reached grade Ⅲ,3 (16.7%) reached grade Ⅳ, and only 1 (5.5%) patient reached grade Ⅴ. When Mchugh grading scores were used to assess the effectiveness of VNS,7 (38.9%) patients reached grade Ⅰ, another 7 (38.9%) patients reached grade Ⅱ, 3 (16.7%) reached grade Ⅲ, and only 1 (5.5%) patient reached grade Ⅳ After surgery of VNS, one patient developed hoarseness but improved significantly after 2 weeks. Another two patients had coughing while the device was activated, and improved when the stimulation parameters were adjusted. One patient developed hiccup in the 5th month after VNS surgery, and got relieved after 2 months. As the result of quantitative EEG, W value of 16 brain divisions and whole brain in the 12th month showed a downward trend compared with the baseline, but no significant difference was identified.ConclusionVNS may be a safe and effective treatment for the drug-resistant epileptic patients with unclear or diffuse epileptogenic zone, or the epileptogenic zone located in important functional areas which were unlikely to be resected.