Vagus Nerve Stimulation

Vagus nerve stimulation

Also called: Vagal Nerve Stimulation

Summary

Vagus nerve stimulation (VNS) is a treatment method that involves placing a small electrical device (similar to a pacemaker) in the body to stimulate the vagus nerve. The vagus nerve runs from the brain to the abdomen, passing through numerous organs. It is one of the most important nerves in the body. It is thought that stimulating the vagus nerve may help to treat disorders of the brain and nervous system. Currently, VNS is approved by the Food and Drug Administration (FDA) to treat epilepsy and some forms of chronic depression. Its effectiveness is still being evaluated, particularly with respect to depression.

The stimulator is inserted into the chest and its electrodes are placed around the vagus nerve in the neck. This surgical procedure is usually performed under general anesthesia, although sometimes it is done under local anesthesia. The device is programmed to stimulate the nerve at regular intervals. Patients are supplied with a magnet, which they can use to deliver extra stimulation when needed (if, for example, they feel a seizure coming on). The magnet can be used to turn the device off.

The most common side effects from VNS include:

  • Hoarseness
  • Sore throat
  • Change in voice tone during stimulation
  • Tickling in the throat

These side effects are usually mild and generally subside over time.

VNS can be used to help control seizures that have not responded to seizure medication or conventional brain surgery. It can also be used to treat severe medication-resistant depression. In both cases, medication is still required to control symptoms. Studies are currently under way to test the effectiveness of vagus nerve stimulation for the treatment of migraines, chronic pain and Alzheimer’s disease. People with vagus nerve stimulators should not experience any problems with microwaves, cell phones or airport metal detectors. However, they should take extra precautions when undergoing magnetic resonance imaging (MRI) scans and certain forms of heat therapy. These procedures can heat the electrodes of the device and damage the vagus nerve or the surrounding tissue.

About vagus nerve stimulation

Vagus nerve stimulation (VNS) is a treatment method to stimulate the vagus nerve using a surgically implanted small electrical device (similar to a pacemaker). VNS has been approved by the Food and Drug Administration (FDA) to treat epilepsy characterized and certain cases of severe, chronic depression. VNS is used in addition to seizure medications.

The therapy has been shown to reduce seizures in some people with epilepsy by approximately 20 to 40 percent, according to the National Institutes of Health (NIH). VNS is not a cure for epilepsy, its use is meant for cases that do not respond to medication or brain surgery. The effect of VNS on depression is less clear. More studies are necessary to determine what impact VNS may have for the treatment of depression. Roughly 32,000 people have the vagus nerve stimulation device implanted, most of of them implanted for the treatment of epilepsy, according to the Epilepsy Foundation.

The vagus nerve is one of the most important nerves in the body. It is a paired nerve that runs down each side of the spinal cord from the brainstem to the abdomen, passing through numerous organs and transmitting information from these organs to the brain. The vagus nerve controls functions such as heartbeat, gag reflex and digestion. It is also thought that the vagus nerve is associated in some way with serotonin, a chemical in the brain responsible for controlling mood, sleep and appetite.

A vagus nerve stimulator is a small battery-like device with silicone-coated electrodes attached, measuring about 2 inches (5 centimeters) diameter. The stimulator is inserted into the left side of the chest and the electrodes are placed around the vagus nerve in the neck. When the stimulator is turned on, it sends small pulses of electricity through the electrodes and into the vagus nerve at regular intervals (e.g., 30 seconds of stimulation every five minutes), 24 hours a day.

Patients are given a magnet, which they can use to turn the device on or off. The magnet can be worn like a watch or a belt. It can also be used to deliver stimulation in between the normal intervals. This is especially useful for those able to sense when their seizures are about to occur.

The batteries of the stimulator usually require replacement every six years. The device itself may last up to 12 years, according to the manufacturer.

Much like other epilepsy treatments, it is unclear exactly how VNS works to control seizures or reduce depression. Stimulating the vagus nerve may increase blood flow to several parts of the brain that may play a role in seizure activity and mood.

VNS was first approved for treatment of generalized seizures. It is now believed that vagus nerve stimulation can be used to treat numerous types of seizures and research is being conducted into other possible uses.  

Side effects are usually mild and decrease over time. Many people experience a change of voice tone during stimulation because the vagus nerve controls many aspects of vocal function. For this reason, vagus nerve stimulation may not be suitable for people who rely on their voices, such as singers or public speakers. Unlike pacemaker devices, vagus nerve stimulators are not affected by cell phones, metal detectors, microwave ovens or other common electrical devices.

Conditions treated with vagus nerve stimulation

The full potential of VNS therapy is not fully known. Because of the range of brain and body functions controlled by the vagus nerve, it is thought that vagus nerve stimulation could be used as a treatment method for a variety of medical conditions. To date, the Food and Drug Administration (FDA) has only approved the use of vagus nerve stimulation to treat epilepsy and some cases of severe depression.

Epilepsy is a neurological disorder that involves a tendency to experience recurrent seizure activity in the brain. This can be the result of an underlying medical condition or injury, which makes a person susceptible to recurring seizures. In many cases, the cause is unknown.

VNS therapy may be recommended to reduce seizures when medication or conventional brain surgery is not effective. It is usually considered as an option for patients who have tried two or more medications and who are unsuitable for or unwilling to undergo brain surgery. Vagus nerve stimulation is a form of add-on therapy, which means that it must be used in conjunction with other forms of seizure control, such as seizure medications or brain surgery. Research indicates that this treatment, used with seizure medication, is able to reduce seizures by up to 40 percent in some people. However, in others, vagus nerve stimulation does not work as well, with some patients reporting no change or a worsening of their seizures. It is unclear why vagus nerve stimulation works better for some patients than for others.   

Vagus nerve stimulation is also used to treat severe chronic depression, which is characterized by an altered, usually profoundly sad mood and a loss of interest or pleasure in activities that were once enjoyable. Vagus nerve stimulation was first explored as an option for treating depression when it was observed that some people with epilepsy who underwent the treatment experienced a general improvement in mood, even if the device had no effect on the patient’s epilepsy.

Vagus nerve stimulation is generally considered as a treatment option for severe depression that has not responded to at least four other treatment methods. However, despite FDA approval, the evidence is inconsistent in demonstrating that vagus nerve stimulation is an effective treatment method for severe chronic depression.

There is also some evidence to suggest that vagus nerve stimulation could be used to treat intractable migraines, fibromyalgia, chronic pain and Alzheimer’s disease although its use for these purposes has yet to complete clinical trials and is not approved by the FDA.

Before and during vagus nerve stimulation

The insertion of the stimulator is usually performed under general anesthesia (when the patient is asleep). In most cases, patients will be asked to sign a consent form and to stop eating and drinking after midnight prior to the procedure. Certain medications may need to be reduced or stopped temporarily, so patients should discuss their medication schedules with their neurologist or other physician before surgery. Patients wear a hospital gown for the insertion and will be asked to remove dentures, jewelry, nail polish and/or glasses.

Some surgeons use local anesthetic for the procedure. In these cases, the patient will be awake during the procedure but will not feel any pain.

During the procedure, the surgeon will make two small cuts (incisions). One incision will be made at the neck where the vagus nerve will be accessed. The other incision will be made on the left side of the chest either below the collarbone or at the armpit. The device is then placed by the surgeon under the skin in the chest wall. The small electrodes (leads) connected to the device are carefully threaded up through the patient’s neck. Using the incision in the neck, the surgeon is then able to wrap the ends of the leads around the vagus nerve. The incisions at both sites are closed with stitches. The entire procedure usually takes one or two hours and may be performed as an in-patient or out-patient procedure, typically with hospital discharge on the same day as the surgery.

After vagus nerve stimulation

The stimulator is typically not turned on immediately after the procedure. It is generally activated approximately two to four weeks following initial placement. After the stimulator has been turned on, the physician may ask that the patient return for check-ups regularly (e.g., every two weeks) for a period of time. However, once the physician and patient are satisfied that the stimulator is working properly, check-ups can be scheduled every two to six months, or as needed. Rejection of the device by the immune system is typically not an issue because the device is made from titanium, which is unlikely to cause immune system responses.

During routine check-ups, the stimulator may need to be adjusted to produce more or less stimulation. The amount of stimulation is usually increased as the patient’s tolerance increases. This non-invasive procedure can be carried out in the physician’s office. The physician makes any necessary changes on a computer and then places a programming wand over the stimulator to reprogram the device.

Most patients experience some side effects from vagus nerve stimulation (VNS) therapy. The most common side effects are hoarseness, tickling in the throat and shortness of breath. Some people also experience a change in the sound of their voice while the vagus nerve is being stimulated. These side effects are normal and are considered tolerable for most people. Most side effects lessen over time.

There have been instances of patients developing sleep apnea (a disturbance in breathing patterns while sleeping). This can be particularly dangerous for people with epilepsy because lack of sleep is known to trigger seizures. A physician should be consulted if the patient appears to show signs of sleep apnea.

Some patients may not notice any significant improvement in their condition for several months following the procedure. The brain may not begin to react to the stimulation for at least three months, after which time brain activity begins to gradually change. It may take up to two years for patients to notice the effects of VNS.

Benefits and risks of vagus nerve stimulation

For many people, vagus nerve stimulation (VNS) is an effective and minimally invasive treatment option for controlling seizures or depression that has resisted treatment through other methods. One of the most significant benefits of the treatment is the lack of severe side effects that often accompany treatment for both epilepsy and depression.

VNS used to treat seizures must be used in conjunction with seizure medication, but patients may be able to reduce their dosage, which may reduce some side effects of their seizure medication. Additionally, people who are using vagus nerve stimulation to treat severe chronic depression may be able to reduce the dose of antidepressants.

However, there are certain risks that are associated with vagus nerve stimulation. One of the most significant risks is the use of diathermy in people with implanted stimulators. Diathermy is a common type of heat therapy used to treat various forms of pain and inflammation. During diathermy treatment, microwaves, shortwaves or ultrasound are selectively absorbed by tissues with high water content. This therapy can be particularly dangerous for people with nerve stimulators as it may cause the device to heat up and damage the vagus nerve or surrounding tissue. This could result in a loss of vocal cord function or, depending on the extent of the damage, even death. People with vagus nerve stimulators should consult with their physician before undergoing any type of heat treatment on any part of the body.

People with vagus nerve stimulators should also take precautions when undergoing an MRI (magnetic resonance imaging) scan. There is a chance that the MRI may heat the electrodes of the stimulator and cause damage to the nerve or tissue. Generally, the VNS should be turned off prior to undergoing an MRI examination. Other imaging tests, such as x-rays or ultrasounds, are not thought to cause the same problems. However, because of the placement of the device, it may interfere with the results of some imaging tests such as a chest x-ray or a mammogram. People with vagus nerve stimulators should always inform health professionals about their device before any procedures are begun.

Questions for your doctor regarding VNS

Preparing questions in advance can help patients to have more meaningful discussions with their physician regarding their conditions and treatments. Patients may wish to ask their doctor the following questions related to vagus nerve stimulation:

  1. Will my seizures stop with vagus nerve stimulation?
  2. Will you recommend cutting back my medication if the therapy appears to work?
  3. How long is it going to take before I see improvements in my symptoms?
  4. How much should I use the magnet to control the vagus nerve stimulator?
  5. What should I do if my vagus nerve stimulator seems to stop working?
  6. How will I know when the batteries need replacing?
  7. What should I do if my condition worsens after the vagus nerve stimulator is implanted?
  8. Are there any maintenance issues with the vagus nerve stimulator?
  9. Will my stimulator interfere with any medications I am taking?
  10. Will I need the vagus nerve stimulator for the rest of my life?
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