FDA Panel Backs Deep Brain Stimulator for Tremors
http://www.reutershealth.com/news/docs/199703/19970317rga.html
ROCKVILLE, MD, Mar 17 (Reuters) - The Food and Drug
Administration's Neurological Devices panel on Friday voted 8-0
to recommend approval of an implantable device known as a deep
brain stimulator that helps control tremors in patients with
Parkinson's disease and essential tremor.
The panel was split on whether the device should be implanted on
both sides of the brain, citing a lack of data. The $10,000
device, called the Activa Tremor Control System, will be made and
sold by Medtronic Inc., and will only be recommended for patients
refractory to drug therapies for the conditions.
The FDA does not have to follow the panel's advice, but usually
does. Panel members said they thought results were more
impressive in essential tremor than in Parkinson's. Even so, Dr.
Mark Hallet, a panelist and clinical director of the National
Institute for Neurological Disorders and Stroke, said that he
felt "...the benefit is clear," for all tremors, outweighing any
safety risk.
Committee members were concerned, however, about the potential
for intracranial hemorrhage during implantation. During trials
that involved 418 patients, 13 had ICH. In addition, panel member
Dr. Gilbert Gonzalez, a neurologist from the Mayo Clinic in
Scottsdale, Ariz., said that he was not convinced that it was
safe to implant a polyurethane device into the brain.
With Activa, electrodes implanted in the brain -- usually in the
thalamus -- are then connected to a pulse generator, which is
implanted subcutaneously in the chest. Medtronic says that Activa
is an option to drugs such as levodopa, and to surgical
techniques such as thalamotomy. With the Activa system, there is
little to no damage to the brain with implantation, according to
Medtronic and to an FDA reviewer. And, patients can turn off the
device at any time, by passing a hand-held magnet over the
generator. This helps control side effects due to the impulses,
which include paraesthesia, paresis and dysarthria.
The firm presented data from two trials, both relatively small.
All patients received an Activa implant, but patients and
physicians were blinded as to whether stimulation was activated
at time of evaluation. Panel members said they did not consider
this a true randomization, but accepted the results anyway. In
the studies, conducted in the U.S. and Europe, both Parkinson's
and essential tremor patients had two-point drops on the
four-point Unified Parkinson's Disease scale and the Tremor
Rating Scale, said Medtronic clinical investigator Dr. William
Koller of the University of Kansas.
The firm studied 45 U.S. patients at several sites, all of whom
received unilateral implantation. In the European study, 28
patients got unilateral, and 18 got bilateral implantation.
Koller said that ,for many essential tremor patients, results
were so significant that it was "...like pushing the disease back
twenty years."
An FDA medical reviewer said that, at every follow-up point,
57.7% of essential tremor patients had at least a two-point
decrease on the symptom scale. For Parkinson's patients, at least
60% of patients had a similar drop. The reviewer expressed
concern that 7 of the Parkinson's patients had worsening tremors,
and that most did not experience any improvement in other
symptoms, or in ability to carry out activities of daily living
such as bathing.
But Medtronic and some panelists pointed out that tremor is only
one symptom of Parkinson's and that Activa was not designed to
address any other symptoms. Activa is already approved in Europe,
Australia, and Canada for use in both essential tremor and
Parkinson's.
- Westport Newsroom 203 221 7648
---------------
New Brain Clue to Making Choices
http://www.reutershealth.com/news/rhdn/199703/1997031310.html
NEW YORK, March 13 (Reuters) -- Scientists may have come close to
understanding a biochemical process in the brain that influences
the ability to make the right decisions -- to predict what
behavioral choices may be most useful for survival.
A series of experiments on monkeys reported in the journal
Science indicate that brain cells which secrete the
neurotransmitter dopamine play a key role in this process,
signaling the best course of action for a given situation.
The new explanation for how people come to read sensory clues
around them and choose from a number of behaviors for maximum
benefit are based on more than 15 years of primate experiments in
Switzerland, says Dr. P. Read Montague, professor of neuroscience
at Baylor College of Medicine in Houston, Texas.
In these experiments by Montague's co-author Dr. Wolfram Schultz
of the University of Fribourg, electrodes were attached to the
brains of monkeys to record electrical activity in
dopamine-secreting brain cells (neurons). The monkeys were
trained to press a level in response to a certain pattern of
light to receive a reward (a squirt of juice).
"And the electrical activity in these neurons is known to reflect
the delivery of this chemical, dopamine, to the frontal cortex.
Dopamine is one of several neurotransmitters thought to regulate
emotional response, and is suspected of playing a central role in
schizophrenia, Parkinson's disease, and drug abuse," Montague
says. "We think these dopamine neurons are making guesses at
likely future rewards. The neuron is constantly making a guess at
the time and magnitude of the reward."
"If what it expects doesn't arrive, it doesn't change its firing.
If it expects a certain amount of reward at a particular time and
the reward is actually higher, it's surprised by that and
increases its delivery of dopamine," he explains. "And if it
expects a certain level (of reward) and it actually gets less, it
decreases its level of dopamine delivery."
Thus, says Montague, "what we see is that the dopamine neurons
change the way they make electrical impulses in exactly the same
way the animal changes his behavior. The way the neurons change
their predictions correlates with the behavioral changes of the
monkey almost exactly."
Montague and MIT co-author Dr. Peter Dayan pulled together
Schultz's findings and created a mathematical theory based on the
idea of those neuronal guesses and then compared it to what was
actually recorded in primates. "It dead-on predicts the way those
cells are going to fire," Montague says.
The researcher notes further evidence supporting the theory comes
from recent brain-scan studies of people who are missing parts of
their frontal cortex.
"They're missing the part of their frontal cortex that provides
input to these dopamine neurons in their midbrain," says
Montague. "And interestingly enough, these people lack the
ability to make correct decisions about the future when you give
them psychological tasks asking them that -- which is exactly
what you'd predict from the way we construe these neurons."
Montague says the findings in primates may also increase our
understanding of the brain mechanisms affected by drug abuse.
"This is an important piece of the puzzle because we know
dopamine is involved in the same systems that are usurped by
drugs of abuse, like cocaine."
SOURCE: Science (1997;275:1593-1598)
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