The following is a paper from The Hospital of the Good Samaritan in Los
Angeles on their experience with pallidotomies
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ELECTROPHYSIOLOGICAL CONTROL FOR PARKINSON'S DISEASE
by Oleg Kopyov, M.D., Ph.D
The Neurosciences Institute
Hospital of the Good Samaritan, Los Angeles
Pallidotomies have been performed as a treatment for Parkinson's disease for
over 40 years. In 1953, the first cases of chemical and electrical
coagulation of the pallidum in patients with Parkinson's were published:
these patients remained free of symptoms for more than two years. As a
result of these reports, the pallidotorny became a popular procedure in the
1950's, but later most neurosurgeons abandoned it because of inconsistent
results. The benefits of pallidotomies were inconsistent due to problems
with stereotactic localization and image techniques. Standard atlases of the
brain do not take into account differences between patients. Recent advances
in imaging techniques and electrophysiological recording equipment now used
for the pallidotomy create the potential for far more constant benefits.
The Hospital of the Good Samaritan has now refined a state-of-the-art
pallidotomy procedure which includes the following major steps:
(1)To obtain a clear image of the patient's brain and to plot approach to the
target - a specific region of the internal portion of the globus pallidus,
located approximately 65 mm into the brain. At the Hospital of the Good
Samaritan, this step is performed employing a very reliable software called
the "Gamma Plan," which allows us to calculate stereotactic coordinates of
the globus pallidus based on multiple MRI slices - multiple images of
different parts of the patient's brain.
(2)To insert the microelectrodes into the patient's brain in accordance with
precise coordinates and recorded signals from individual brain cells. Cells
in each particular area of the brain have a known and unique pattern of
activity. The sophisticated data acquisition system tells us what part of
the brain the microelectrode is in by allowing us to hear the discharge
pattern of the cells, which is amplified, sent to a loud speaker and then
displayed on the screen of the oscilloscope. Both the sounds of the neuronal
activity and the form of the electrical waves have readily recognizable
patterns, The visual and acoustic recognition will be supported by the online
computer analysis of many thousands of electrical signals produced by these
neurons as well. For example, when advancing through one region of the brain
into another, the microelectrode will enter a zone between the two areas that
produces no sound because it contains no cells. When the microelectrode
leaves one area in which cells are firing and enters this quiet zone, the
neurosurgeon knows exactly where the microelectrode is. These
electrophysiological measurements allow the neurosurgeon to adjust the
calculated microelectrode path to the specific conditions of the patient's
brain and to test the functional role of the discovered group of cells
responsible for Parkinson's symptoms.
(3) The procedure includes mapping the boundaries of both the globus
pallidus and the location of cells within the structure that respond to
voluntary or passive movements of the arms and legs. For this reason, the
patient is given only local anesthesia and remains awake during this process.
When electrical stimulation is applied through the tip of the microelectrode,
the neurosurgeon asks the patient to report any sensation, The optimal target
appears to lie in the posteroventral portion of the globus pallidus in most
patients.
(4) After the precise location has been determined and tested, a large
lesion electrode is introduced into the area. The tip of the lesion
electrode is heated in order to deaden several millimeters of the surrounding
tissue. This almost immediately lessens the Parkinsonian symptoms. The
tremors and muscular stiffness are reduced, and the patient is able to move
spontaneously once again. Speech, gait and balance can benefit as well.
At the Hospital of the Good Samaritan, further refinement of this technique
is achieved through the computerized overlay of the electrode's pathway on
the patient's brain MR image. This allows the neurosurgeon to reliably
evaluate the electrode location in the brain at any moment of the procedure,
While all these steps transform the pallidotomy into an efficient and safe
treatment for Parkinson's disease, additional research is currently underway
at Good Samaritan that will simplify the pallidotomy procedure but will
reduce none of the precision and benefits.
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Greg Johnson
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