Vagus nerve stimulation (VNS) therapy
There are several ways to treat epilepsy, and how well each treatment works varies from one person to another. Vagus Nerve Stimulation (VNS) therapy is a form of treatment for epilepsy for people whose seizures are not controlled with medication.
What are the vagus nerves?
The vagus nerves are a pair of nerves that start in the brain and run through the body. They send and receive messages between the brain and the body.
What is VNS therapy and how does it work?
Vagus nerve stimulation (VNS) therapy is a type of treatment for epilepsy that involves a stimulator (called a pulse generator) which is connected, inside the body, to the left vagus nerve. The stimulator sends regular, mild electrical stimulations to this nerve.
The electrical signals travel through leads to the electrodes, which are wrapped around the vagus nerve in the neck. Here the electrical signals follow the fibres of the vagus nerve as they enter the brain at the top of the spinal cord through the medulla (part of the brain stem, which connects the brain to the spinal cord). Many of the vagus nerve fibres end within a part of the brain called the 'nucleus of the tractus solitarius' (NTS). From here, the signals travel to areas of the brain thought to be involved in causing seizures, and so may interrupt seizures or stop them developing in the first place.
What is the aim of VNS therapy?
VNS therapy aims to reduce the number, length and severity of seizures. For some people their seizures become much less frequent, for some it may reduce their seizures a little, and for others it has no effect. VNS therapy may reduce the length or intensity of seizures, but this does not happen for everyone. It may also reduce the time it takes to recover after a seizure. It is unlikely to completely stop seizures and it does not ‘cure’ epilepsy.
The effect of VNS therapy may not happen straightaway; it can take up to two years for it to have an effect on someone’s seizures. It is used alongside anti-epileptic drugs (AEDs) not instead of them. If VNS therapy works, it may be possible to reduce a person’s AEDs over time.
Can I be considered for VNS therapy?
VNS therapy is usually considered if you have tried a number of AEDs which have not fully controlled your seizures, and if you are not suitable for, or do not want to have, brain surgery.
People who are considering VNS will usually be given information about VNS from their neurologist or epilepsy specialist nurse.
What is the stimulator like?
The stimulator is a bit like a heart pacemaker. It is implanted (placed) under the skin in the upper chest (under the left collar bone) during a small operation under general anaesthetic.
Because of the size of the stimulator there will be a small lump where it lies, and a small scar where it was put in. A lead connects the stimulator in the chest to the vagus nerve in the left side of the neck. Because the electrodes are coiled around the nerve in the neck, there will be a small scar where they are inserted, usually in the fold of the neck.
How does the stimulator work?
The stimulator is usually switched on within four weeks of it being implanted. The doctor or nurse will programme the stimulator using a small hand-held computer, and set the amount (strength and length) of the electrical stimulation given. The amount of stimulation varies from person to person but is usually started at a low level and slowly increased to a suitable level for each person. Usually it is set at 30 seconds of stimulation every five minutes through the day and night.
The stimulator has a battery inside it, which can last up to ten years. When the battery is low the stimulator needs to be replaced, during an operation similar to when it was put in.
What can VNS therapy do during a seizure?
Some people have a warning or aura: a simple focal (or 'simple partial') seizure that tells them that they are going to have a further seizure. When this happens, they can pass a special magnet over the stimulator gives extra stimulation. This may stop the aura from developing into another seizure, or may reduce how long it takes to recover afterwards.
The magnet can be worn on their wrist like a watch, or on their belt. For people who have no warning before a seizure, someone else could use the magnet when a seizure happens.
Does VNS therapy have any side effects?
VNS therapy can cause side effects but usually only during the time that the nerve is being stimulated. Side effects may not happen for everyone but include discomfort in the throat, a cough, difficulty swallowing and a hoarse voice.
Side effects may reduce over time and do not usually mean that the stimulator has to be switched off. If side effects are a problem the doctor or nurse can adjust the settings or the magnet can be held over the stimulator for a few seconds, to briefly stop the stimulation.
VNS therapy does not affect, and is not affected by, anti-epileptic drugs. Because it is not a medication it doesn’t affect cognition (a person’s awareness or speed of thought). Also, because it works directly on the vagus nerve it doesn’t have to ‘travel’ around the body to get to the nerve, which reduces the effect on other areas or organs.
What about any other positive effects?
Some people feel that VNS therapy improves their mood, memory or alertness, and may also help reduce depression or have a positive effect on their quality of life (overall wellbeing).
These effects are being researched to see if it can be used in other ways in the future.
What happens if it does not work?
VNS therapy does not work for everyone. If there is no improvement in seizures after two years, the specialist may consider having the stimulator switched off or removed. Even if VNS therapy has no effect on the seizures, it might have other positive effects (see question above).
Can I have an MRI scan?
Magnetic Resonance Imaging (MRI) uses strong magnetic fields to take images of the brain. As the stimulator includes metal, there is a risk that the magnetic field in the MRI machine could cause the electrodes to heat up. The risk of this depends on the MRI machine used. Some types of MRIs may be possible if they just scan the head (rather than scanning the whole body), and they do not scan your neck or chest (where the stimulator lies).
If you have VNS therapy and need an MRI, it is important that everyone involved with the scan is aware, so that they can decide if the scan can be done. If the scan can be done, the stimulator will need to be switched off before the scan, and turned back on again afterwards.
X-Rays and CT scans do not affect, and are not affected by VNS therapy.
FABLE (For A Better Life with Epilepsy)
0800 521 629 (Advice line)
Information and support for people with epilepsy or using VNS therapy.
Cyberonics (makers of the VNS therapy system)
Provides information about VNS therapy.
Original image by kind permission of Cyberonics.
© Epilepsy Society
Information produced in May 2012