Deep Brain Stimulation for
Movement Disorders
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
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
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, the Cleveland Clinic's team goes 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.
Summary
One of the major problems in this area of medicine is that often patients and
their physicians give up too early. Deep brain stimulation offers patients new hope. There
is evidence that these surgeries are as effective as or more effective than older
thalamotomy and pallidotomy, which are well established and accepted treatments. However,
deep brain stimulation may be safer. Patients who fail to achieve satisfactory control
with medications, by which is meant being able to do the things that make them happy,
should consider deep brain stimulation.
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