Vagus Nerve Stimulator (VNS)
Of all the surgical devices listed here, VNS has been around the longest and has been used in maximum number of patients.
How it works: Vagus nerve is a large nerve in the neck (one on each side), which has widespread connections within the brain. Scientists discovered that by regular low intensity electrical stimulation of the vagus nerve, brain excitability towards seizures could be reduced over time.
The VNS is a hockey-puck sized device with an inbuilt battery (some models are smaller). The device is placed under the skin on (usually) the left side of the chest. A thin wire is tunneled under the skin the device to the vagus nerve on the same side. Thus, the patient has two areas of small surgeries- 1) Left side of the chest and 2) the left side of the neck to attach wires to the vagus nerve. No brain surgery is done. After a brief period to allow healing of the scars, the device is switched on.
The device is programmable and can be adjusted to provide the electrical stimulation like clockwork. The doctor can decide several settings such as the intensity of the current, duration of the current, time interval of stimulation etc. To maximize patient comfort, the current settings are usually increased in small increments over several weeks. A typical setting may involve low intensity current stimulation lasting for 30s once every 5 min. Patients are also provided a specialized magnet to activate the device for brief pre-set period and provide ‘extra dose’, perhaps around the time of a seizure or warning symptom. The device has 5 current models. The more recent models, though working on the same principal of regular vagal nerve stimulation, may allow more flexibility of settings such as reduced stimulation during certain hours, heartrate detection and extra stimulation with heart rate changes (which may be caused by a seizure).
Though VNS may not make a patient seizure free, it can significantly reduce the occurrence of seizures. In earlier studies patients reported average of nearly 25% reduction in seizures in the first 3 months of device placement. The benefit may improve with time and nearly 60% patients reported reduction of seizures by at least half by 3 years of device placement. Patients may also report improved quality of life, as tested by standardized questionnaires.
The surgery and the device are usually well-tolerated. After surgery, a small risk of infection or surgery related complication maybe seen which may be easily controlled. When the device is delivering the current, patients may notice temporary change in voice, cough, tickling in throat etc. Usually these symptoms reduce in time and patients do not notice them or are not troubled by them. Adjustments to the current settings may also be helpful. Patients who find the device effective replacement of the device will be needed after the battery drains out, usually once every 3-5 yrs. depending upon the device setting and usage.
Of all the three devices available for treatment of epilepsy only VNS has current approval for use in children and in patients with generalized epilepsy.
Wheless JW, Gienapp AJ, Ryvlin P. Vagus nerve stimulation (VNS) therapy update. Epilepsy Behav. 2018 Nov;88S:2-10.
Schulze-Bonhage A. Long-term outcome in neurostimulation of epilepsy. Epilepsy Behav. 2019 Feb;91:25-29.