Vagus nerve stimulation to treat seizures, epilepsy and mental illness
Vagus nerve stimulation involves the use of a device to stimulate the vagus nerve with electrical impulses. An implantable vagus nerve stimulator is currently FDA-approved to treat epilepsy(لینک به مقاله صرع) and depression. There's one vagus nerve on each side of your body, running from your brainstem through your neck to your chest and abdomen. In conventional vagus nerve stimulation, a device is surgically implanted under the skin on your chest, and a wire is threaded under your skin connecting the device to the left vagus nerve. When activated, the device sends electrical signals along the left vagus nerve to your brainstem, which then sends signals to certain areas in your brain. The right vagus nerve isn't used because it's more likely to carry fibers that supply nerves to the heart. New, noninvasive vagus nerve stimulation devices, which don't require surgical implantation, have been approved to treat epilepsy, depression and pain.
What is the vagus nerve?
There are 12 cranial nerves in the body. They come in pairs and help to link the brain with other areas of the body, such as the head, neck, and torso. Some send sensory information, including details about smells, sights, tastes, and sounds, to the brain. These nerves are known as having sensory functions. Other cranial nerves control the movement of various muscles and the function of certain glands. These are known as motor functions. While some cranial nerves have either sensory or motor functions, others have both. The vagus nerve is such a nerve. The cranial nerves are classified using Roman numerals based off of their location.
Vagus nerve anatomy and function
The word “vagus” means wandering in Latin. This is a very appropriate name, as the vagus nerve is the longest cranial nerve. It runs all the way from the brain stem to part of the colon. The sensory functions of the vagus nerve are divided into two components:
- Somatic components: These are sensations felt on the skin or in the muscles.
- Visceral components: These are sensations felt in the organs of the body.
Sensory functions of the vagus nerve include:
- providing somatic sensation information for the skin behind the ear, the external part of the ear canal, and certain parts of the throat
- supplying visceral sensation information for the larynx, esophagus, lungs, trachea, heart, and most of the digestive tract
- playing a small role in the sensation of taste near the root of the tongue
Motor functions of the vagus nerve include:
- stimulating muscles in the pharynx, larynx, and the soft palate, which is the fleshy area near the back of the roof of the mouth
- stimulating muscles in the heart, where it helps to lower resting heart rate
- stimulating involuntary contractions in the digestive tract, including the esophagus, stomach, and most of the intestines, which allow food to move through the tract.
why is Vagus nerve stimulation done?
About one-third of people with epilepsy don't fully respond to anti-seizure drugs. Vagus nerve stimulation may be an option to reduce the frequency of seizures in people who haven't achieved control with medications. Vagus nerve stimulation may also be helpful for people who haven't responded to intensive depression treatments, such as antidepressant medications, psychological counseling (psychotherapy) and electroconvulsive therapy (ECT). The Food and Drug Administration (FDA) has approved vagus nerve stimulation for people who:
- Are 4 years old and older
- Have focal (partial) epilepsy
- Have seizures that aren't well-controlled with medications
The FDA has also approved vagus nerve stimulation for the treatment of depression in adults who:
- Have chronic, hard-to-treat depression (treatment-resistant depression)
- Haven't improved after trying four or more medications or electroconvulsive therapy (ECT), or both
- Continue standard depression treatments along with vagus nerve stimulation
Additionally, researchers are studying vagus nerve stimulation as a potential treatment for a variety of conditions, including headaches, rheumatoid arthritis, inflammatory bowel disease, bipolar disorder, obesity and Alzheimer's disease.
How you prepare
It's important to carefully consider the pros and cons of implanted vagus nerve stimulation before deciding to have the procedure. Make sure you know what all of your other treatment choices are and that you and your doctor both feel that implanted vagus nerve stimulation is the best option for you. Ask your doctor exactly what you should expect during surgery and after the pulse generator is in place.
Food and medications
You may need to stop taking certain medications ahead of time, and your doctor may ask you not to eat the night before the procedure.
Before the procedure
Before surgery, your doctor will do a physical examination. You may need blood tests or other tests to make sure you don't have any health concerns that might be a problem. Your doctor may have you start taking antibiotics before surgery to prevent infection.
During the procedure
Surgery to implant the vagus nerve stimulation device can be done on an outpatient basis, though some surgeons recommend staying overnight. The surgery usually takes an hour to an hour and a half. You may remain awake but have medication to numb the surgery area (local anesthesia), or you may be unconscious during the surgery (general anesthesia). The surgery itself doesn't involve your brain. Two incisions are made, one on your chest or in the armpit (axillary) region, and the other on the left side of the neck. The pulse generator is implanted in the upper left side of your chest. The device is meant to be a permanent implant, but it can be removed if necessary. The pulse generator is about the size of a stopwatch and runs on battery power. A lead wire is connected to the pulse generator. The lead wire is guided under your skin from your chest up to your neck, where it's attached to the left vagus nerve through the second incision.
After the procedure
The pulse generator is turned on during a visit to your doctor's office a few weeks after surgery. Then it can be programmed to deliver electrical impulses to the vagus nerve at various durations, frequencies and currents. Vagus nerve stimulation usually starts at a low level and is gradually increased, depending on your symptoms and side effects. Stimulation is programmed to turn on and off in specific cycles — such as 30 seconds on, five minutes off. You may have some tingling sensations or slight pain in your neck and temporary hoarseness when the nerve stimulation is on. The stimulator doesn't detect seizure activity or depression symptoms. When it's turned on, the stimulator turns on and off at the intervals selected by your doctor. You can use a hand-held magnet to initiate stimulation at a different time, for example, if you sense an impending seizure. The magnet can also be used to temporarily turn off the vagus nerve stimulation, which may be necessary when you do certain activities such as public speaking, singing or exercising, or when you're eating if you have swallowing problems. You'll need to visit your doctor periodically to make sure that the pulse generator is working correctly and that it hasn't shifted out of position. Check with your doctor before having any medical tests, such as magnetic resonance imaging (MRI), which might interfere with your device.
Implanted vagus nerve stimulation isn't a cure for epilepsy. Most people with epilepsy won't stop having seizures or taking epilepsy medication altogether after the procedure. But many will have fewer seizures, up to 20 to 50 percent fewer. Seizure intensity may lessen as well. It can take months or even a year or longer of stimulation before you notice any significant reduction in seizures. Vagus nerve stimulation may also shorten the recovery time after a seizure. People who've had vagus nerve stimulation to treat epilepsy may also experience improvements in mood and quality of life. Research is still mixed on the benefits of implanted vagus nerve stimulation for the treatment of depression. Some studies suggest the benefits of vagus nerve stimulation for depression accrue over time, and it may take at least several months of treatment before you notice any improvements in your depression symptoms. Implanted vagus nerve stimulation doesn't work for everybody, and it isn't intended to replace traditional treatments. Studies of implanted vagus nerve stimulation as a treatment for conditions such as Alzheimer's disease, headaches and rheumatoid arthritis have been too small to draw any definitive conclusions about how well it may work for those problems. More research is needed.
For most people, vagus nerve stimulation is safe. But it does have some risks, both from the surgery to implant the device and from the brain stimulation.
Surgical complications with implanted vagus nerve stimulation are rare and are similar to the dangers of having other types of surgery. They include:
- Pain where the cut (incision) is made to implant the device
- Difficulty swallowing
- Vocal cord paralysis, which is usually temporary, but can be permanent
Side effects after surgery
Some of the side effects and health problems associated with implanted vagus nerve stimulation can include:
- Voice changes
- Throat pain
- Shortness of breath
- Difficulty swallowing
- Tingling or prickling of the skin
- Worsening of sleep apnea
For most people, side effects are tolerable. They may lessen over time, but some side effects may remain bothersome for as long as you use implanted vagus nerve stimulation. Adjusting the electrical impulses can help minimize these effects. If side effects are intolerable, the device can be shut off temporarily or permanently.
frequently asked questions
Are there patients who should not receive vagus nerve stimulation treatment?
Relative contraindications may include: pregnancy, asthma, chronic pulmonary disease, active peptic ulcer disease, and insulin-dependent diabetes mellitus.
What is the length of time that a person should wait before considering a vagus nerve stimulator?
There's no particular length of time but rather enough time to show that at least two different seizure medicines, taken consistently at appropriate doses and which are appropriate for a person's type of seizures, are not adequate to control seizures satisfactorily. This determination is best made between each individual patient and their doctor. Under these circumstances, VNS should be discussed along with other options, such as other seizure medicines, the possibility of epilepsy surgery, a special diet, investigational medicines or devices, or lifestyle modifications.
Is there any type of epilepsy that vagus nerve stimulation does not help?
It's only been definitely shown to help partial seizures. It has not been definitively shown to help or not to help other seizure types.