Epilepsy: Vagus Nerve Stimulation (VNS)
What Is Vagus Nerve Stimulation?
Vagus nerve stimulation (VNS) is a technique used to treat epilepsy. It involves implanting a pacemaker-like device that generates pulses of electricity to stimulate the vagus nerve. The vagus nerve is one of the 12 cranial nerves, which conduct impulses between thebrain and other parts of the brain and various body structures, mostly in the head and neck. The vagus nerve - the longest of the cranial nerves - also extends to organs in the chest and abdomen. (The word vagus comes from a Latin word for "wandering.') It serves many organs and structures, including the larynx (voice box), lungs, heart and gastrointestinal tract.
How Is Vagus Nerve Stimulation Done?
While the patient is asleep (general anesthesia), the stimulator device - which is about the size of a silver dollar - is surgically placed under the skin in the upper part of the chest. A connecting wire is run under the skin from the stimulator to an electrode that is attached to the vagus nerve, which is accessible through a small incision (cut) in the neck.
After it is implanted, the stimulator is programmed using a computer to generate pulses of electricity at regular intervals, depending on the patient's tolerance. For example, the device may be programmed to stimulate the nerve for 30 seconds every five minutes. The settings on the device are adjustable, and the electrical current is gradually increased as the patient's tolerance increases. Re-programming the stimulator can be done in the doctor's office. The patient also is given a hand-held magnet, which when brought near the stimulator, can generate an immediate current of electricity to stop a seizure in progress or reduce the severity of the seizure.
VNS is an add-on therapy, which means it is used in addition to another type of treatment. Patients who undergo VNS continue to take their seizure medications. In some cases, however, it may be possible to reduce the dosage of medication.
When Is VNS Used?
Brain cells communicate by sending electrical signals in an orderly pattern. In people with epilepsy, this pattern is sometimes disrupted due either to an injury or the person's genetic make-up, causing brain cells to emit signals in an uncontrolled fashion. This creates over-excitement, somewhat like an electrical overload in the brain, leading to seizures. Seizures can be produced by electrical impulses from throughout the brain, called generalized seizures, or from a small area of the brain, called partial seizures.
Most people with epilepsy can control their seizures with medications called anticonvulsant or anti-seizure drugs. For the 30% of people with epilepsy who either do not respond to anti-seizure medications or cannot tolerate their side effects, surgery to remove the part of the brain causing the seizures may be used. But for people who are not considered good candidates for surgery -- for example, their seizures are produced throughout the brain -- and for those whose seizures are not controlled by medications, VNS may be a treatment option.