Effect of Vagus Nerve Stimulation on Intractable Epilepsy
Authors: Asakura Tetsuhiko , Yatsushiro Kazutaka , Nakamura Katsumi , Shimizu Hiroyuki , Ishijima Buichi , Otsuki Taisuke , Yoshimoto Takashi , Taira Takanori , Kawamura Hirotsune , Takakura Kintomo , Moritake Kozo , Hori Pomokatsu , Taneda Mamoru 
Published: August 2009

Purpose: Since 1993, we have studied the efficacy and safety of vagus nerve stimulation (VNS) with a Neurocyberhetic Prosthesis (NCP) (Cyberonics, U.S.A.) against medically intractable epilepsy first in Japan. We summarize the intermediate results so far acquired in this report.

Methods: Patients with intractable partial seizures were selected as candidates for implantation of the NCP. This type of therapy has been tested in individuals whose seizure activity has not been effectively controlled by pharmacotherapy. The result was a reduction in the rate of seizures in each period compared with the average number of seizures before implantation of the NCP. To avoid nerve fatigue, the upper limits of the parameters were set as follows: frequency, 30 Hz; pulse width, 1,000 μ; on time, 60 s; output current, 3.0 mA. After informed consent, the leads of the NCP were connected under general anesthesia to the cervical portion of the left vagus nerve. Those leads were connected through a subcutaneous tunnel with the NCP implanted subcutaneously on the breast. Thirty‐four patients have been implanted with the NCP, and 31 patients have started stimulation as of September, 1997. We have analyzed the data from 16 male and 15 female patients who were followed up for >6 months with a mean follow‐up period of 20.0 months; their ages ranged from 19 to 52 years with a mean age of 31.2 years. Their types of seizures included 28 complex partial seizures (CPSs), 12 simple partial seizures (SPSs) and 11 secondarily generalized seizures (SGSs). The number of seizures during a month was counted for 3 consecutive months before implantation of NCP. These values were compared with average number of seizures that occurred during the 4–6 months after VNS. We also calculated the patients with a 50% reduction in seizure frequency compared with the baseline.

Results: the mean seizure‐changing rates during the 4–6 months after stimulation were −26.4 2 13.2% (mean ± SEM) in total seizure numbers, −41.9 ± 13.0% in seizure with disturbance of consciousness, −37.0 ± 19.9% in SGSs, −70.4 ± 17.6% in CPSs, and −15.5 ± 16.2% in SPSs. The 50% reduction rates were 48.4% for all seizure types, 63.3% in seizures with disturbance of consciousness, 58.6% in CPSs, 63.6% in SGSs, and 47.1% in SPSs during the 4 4 months after stimulation.

Conclusions: Our early results demonstrated the efficacy and safety of VNS with the NCP in medically intractable epilepsy. We adpated the VNS for intractable epilepsy, and our results demonstrated its efficacy. The reduction of seizures was observed more strongly in the latest 3 months than during the 4–6 months after starting the VNS. This result may be due to the characteristics of VNS or the period when we needed to adjust the parameters of the NCP. The efficacy of VNS during the latest 3 months is better than that of recent antiepileptic agents. However, we have not yet achieved any seizure‐free patients, although their seizure rates have been reduced. We need more experiences with VNS to determine the appropriate parameters and find out how to select the most suitable cases.