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What is a movement disorder?

A movement disorder can be defined as any disease or injury that interferes with a person's movement. By this definition, paralysis could be considered a movement disorder. However, movement disorders typically refer to conditions such as Parkinson's disease, essential tremor or tremor due to problems with a part of the brain called the cerebellum. For example, some patients with multiple sclerosis, which harms nerve fibers in the brain, will have severe tremor.

What are these conditions?

Parkinson's Disease

Parkinson's disease is a common disorder affecting nearly three out of one hundred persons over the age of 65 years. It is becoming increasingly diagnosed in younger persons under the age of 50 years.

Parkinson's disease is caused by degeneration of brain cells that make a chemical called dopamine. When these cells degenerate, the patient runs out of dopamine and develops slowing of movement, difficulty with speech, slowed and shuffling walking and tremor. Parkinson's disease is often very difficult to diagnose because not every patient has all the same symptoms.

Essential tremor is a common movement disorder that usually affects the head, chin, outstretched hands or voice. This disease causes tremor that is disabling in some. The cause of essential tremor is unknown, although it does run in some families.

Multiple sclerosis is another common disease and tends to begin in young adulthood. Multiple sclerosis can affect any part of the central nervous system. When it affects the cerebellum or the cerebellum's connections to other parts of the brain, severe tremor can result.

What is Deep Brain Stimulation?

Deep brain stimulation is a variation of an old surgery. Surgery for Parkinson's disease, essential tremor, and tremor due to multiple sclerosis has been available since the 1960s. Back then, surgery was used to destroy a small part of the brain called the thalamus or another part of the brain called the globus pallidus.

This type of surgery is still done today although less frequently because of the availability of deep brain stimulation. In the case of the thalamus, it is thought that the abnormal brain activity that causes tremor is processed through the thalamus. The surgery, called thalamotomy, destroys part of the thalamus to block the abnormal brain activity from reaching the muscles and causing them to tremor.

The surgery to destroy the globus pallidus is called a pallidotomy. It is thought that the globus pallidus becomes overactive in Parkinson's disease. This overactivity acts like a brake and slows or diminishes movement. Pallidotomy is a way to destroy the overactive globus pallidus to improve the symptoms of Parkinson's disease.

These surgeries are effective but carry significant risks. Both thalamotomy and pallidotomy require purposeful destruction of the brain. If the surgeon is off by even a fraction of an inch, the surgery may not be effective and severe complications such as paralysis, loss of vision, or loss of speech can result.

Deep brain stimulation is a way to inactivate the thalamus or globus pallidus without purposefully destroying the brain. Therefore, the risks are much less. In deep brain stimulation, an electrode is placed with the tip of the electrode in the thalamus (for essential tremor and multiple sclerosis) or in the globus pallidus (for Parkinson's disease). Rather than destroying the brain, small electrical shocks are given. This has the same effect as thalamotomy or pallidotomy without actually destroying parts of the brain.

The electrode for deep brain stimulation is left in the brain. It is connected by a wire to a pacemaker-like device that is implanted under the skin over the chest. The pacemaker-like device generates the electrical shocks.

What are the advantages of Deep Brain Stimulation?

Deep brain stimulation offers a number advantages. The electrical stimulation is adjustable, whereas surgical destruction is not. The electrode has four metal contacts that can be used in many different combinations. Even if one electrode contact is not in the exact location, it is likely that one of the others or some combination of electrical contacts will be closer to the proper target. As the patient's response to surgery changes over time, the stimulation can be adjusted without the necessity of repeat operation.

Another significant advantage of deep brain stimulation relates to future treatments. Destructive surgery, such as thalamotomy or pallidotomy, may reduce the patient's potential to benefit from future therapies. For example, future brain cell transplantation may be of great help to patients with Parkinson's disease. There is concern that a pallidotomy or thalamotomy may prevent patients from benefiting from brain cell transplantation. This would not be the case with deep brain stimulation as the stimulator could be turned off.

What kinds of movement problems are helped by deep brain stimulation?

Because the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body, a stimulator will help only on the opposite side of the body. Most patients will have the stimulator placed in only one side of the brain; a few will have stimulators placed on both sides but not at the same time. The risks for complications increase when stimulators are place in both sides of the brain.

The main purpose of deep brain stimulation for patients with essential tremor and tremor due to multiple sclerosis is to control the tremor of the arm. While tremor of the head and body may be helped, the decision to have surgery should be based on decreasing arm tremor. In the case of multiple sclerosis, other problems such as loss of vision, sensation or strength are not helped by deep brain stimulation. Electrical stimulation does not cure multiple sclerosis nor does it prevent the disease from getting worse.

In Parkinson's disease, the goals are to (1) improve the speed and dexterity of the arm on the side opposite to the stimulator, (2) to reduce tremor, and (3) to block the involuntary movements (called dyskinesia) associated with the medications used to treat Parkinson's disease. Neither deep brain stimulation nor pallidotomy help problems related to walking or balance.

Are these operations experimental?

Deep brain stimulation is not experimental. It has been approved by the Federal Food and Drug Administration (FDA) for stimulation of the thalamus in patients with Parkinson's disease and essential tremor. However, stimulation of the thalamus is not recommended for Parkinson's disease. Instead, stimulation of the globus pallidus is recommended because stimulation of the thalamus only helps with tremor and rigidity. The other symptoms are helped by stimulation of the globus pallidus. Even if a patient currently only has tremor or rigidity, he or she will eventually develop other symptoms that would only be helped by stimulation of the globus pallidus.

Deep brain stimulation of the globus pallidus for patients with Parkinson's disease and stimulation of the thalamus for patients with multiple sclerosis has not been approved specifically by the FDA. However, this does not mean that the treatment is experimental or that it would not be covered by insurance. There are many examples of treatments that are used every day and are standard and accepted but that have not been approved by the FDA.

Who should consider deep brain stimulation?

There are many important issues to be addressed when considering deep brain stimulation. These issues should be discussed with a movement disorders expert or a specially trained neurologist. A movement disorders expert is someone who has trained specifically in movement disorders (such as through a fellowship) or who has done research in or published articles about movement disorders.

One of the most important criteria is that the patient has had an adequate trial of medications. It would be unethical to expose a person to the risks of surgery if medications could give satisfactory control of the disease. However, surgery should be considered for people who do not achieve satisfactory control through medications. If there is any question whether surgery will help, the patient should consult a movement disorders expert or a neurologist who has experience with movement disorders.

Where should the operation be done?

The first and most important recommendation is that the patient has surgery where there is a team of experts. This means neurologists and neurosurgeons who have experience and specialized training in doing these types of surgeries.

The next most important question is how is the surgery done. Different centers may perform the surgeries in different ways. It is very important to ask how the target (that is the thalamus or globus pallidus) is localized. It is clear that the chances of benefit and the risks of complications are directly related to how close the electrode is to the correct target.

How can the target area be localized?

There are several ways in which the target is localized. One way is to rely only on Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scans. While some surgeons stop there, others go further. Prior to placing the permanent stimulating electrode, micro-electrodes are used to record electrical activity generated by individual brain cells. Because these cells communicate by electrical impulses, micro-electrode recording is like eavesdropping on the conversation the brain cells are having. When just the right accent (just the right pattern of brain cell activity) is identified, the surgeon can be confident that the electrode is in the best location.

With modern CT and MRI techniques, the surgeon can get close, but the use of micro-electrode recordings will get the surgeon closer. While surgeons who use only the CT or MRI scans will have some success, the rate of success is greater and the risk of complications less when micro-electrode recordings are used. Micro-electrode recordings do take more time (and therefore, it is less popular with some surgeons) but, in our opinion, the extra time is worth it.

There are two types of electrical recording that can be done. One type is with the micro electrodes described above. Another type is with macro-electrodes. These electrodes have a larger tip. Because of their size, they cannot record the electrical activity of individual brain cells but instead record the activity of many brain cells. Using macro-electrodes would be like hearing the roar of a crowd, whereas using the micro-electrodes is like listening to the individual conversations. In our opinion, using the micro-electrodes and listening to the conversations of individual brain cells is more accurate.

Vagus nerve stimulation (VNS) is designed to prevent seizures by sending regular, mild pulses of electrical energy to the brain via the vagus nerve. These pulses are supplied by a device something like a pacemaker.

The VNS device is sometimes referred to as a "pacemaker for the brain." It is placed under the skin on the chest wall and a wire runs from it to the vagus nerve in the neck.

The vagus nerve is part of the autonomic nervous system, which controls functions of the body that are not under voluntary control, such as the heart rate. The vagus nerve passes through the neck as it travels between the chest and abdomen and the lower part of the brain.

What is the surgery like?

The surgeon first makes an incision along the outer side of the chest on the left side, and the device is implanted under the skin. Then a second incision is made horizontally in the lower neck, along a crease of skin, and the wire from the stimulator is wound around the vagus nerve in the left side of the neck. The brain itself is not involved in the surgery.

The device (also called an implant) is a flat, round battery, about the size of a silver dollar—that is, about an inch and a half (4 cm) across—and 10 to 13 millimeters thick, depending on the model used. Newer models may be somewhat smaller.

The procedure usually lasts about 50 to 90 minutes with the patient under general anesthesia. Sometimes a hospital stay of one night is required. Some surgeons have performed the procedure with local anesthesia and the patient has been discharged the same day.

How is Vagus Nerve Stimulation (VNS) used?

The neurologist programs the strength and timing of the impulses according to each patient's individual needs. The settings can be programmed and changed without entering the body, just by using a programming wand connected to a laptop computer.

For all patients, the device is programmed to go on for a certain period (for example, 7 seconds or 30 seconds) and then to go off for another period (for example, 14 seconds or 5 minutes). The device runs continuously, usually with 30 seconds of stimulation alternating with 5 minutes of no stimulation. The patient is usually not aware that it's operating.

Holding a special magnet near the implanted device causes the device to become active outside of the programmed interval. For people with warnings (auras) before their seizures, activating the stimulator with the magnet when the warning occurs may help to stop the seizure. Many patients without auras also experience improved seizure control, however.

Settings (also called stimulation parameters) set by the neurologist typically include a stimulation amplitude of 1.0 to 3.0 mA (milliamperes), a stimulation frequency of 30 Hz (hertz), and a pulse width of 500 microseconds. By adjusting these settings, the doctor not only may be able to control more of the patient's seizures, but often can also relieve side effects. One study, for instance, found that changing the pulse width eliminated pain that some patients were experiencing. The battery for the stimulator lasts approximately 5-10 years.