 "Surgeons
guided by a CT scan insert two electrodes into the cortical
area of the brain in or near the seizure focus. Then they
connect the electrodes by thin wires under the skin to
a battery pack embedded in the patient's chest."
Dr Douglas Labar's description
of a novel epilepsy treatment would likely strike fear
into the hearts of most patients. But for the roughly
one-third of Canada's 200,000 epilepsy sufferers who
don't respond to anti-epileptic drugs (AEDs), electronic
deep brain stimulation (DBS) could be a dream come true.
Early results from the ongoing
Intercept trial, which Dr Labar is leading, are offering
a fresh glimmer of hope to these patients, who continue
to struggle with seizure control. It's the first clinical
trial of DBS for epilepsy.
EARLY
PROMISE
The study, conducted at the New York-Presbyterian/Weill
Cornell Medical Center, uses the Intercept Epilepsy
Control System developed by Medtronic, Inc. Preliminary
work with the system, published in Epilepsia in
2004, found that four out of five epilepsy patients
treated with DBS improved significantly with no side
effects. Best of all, they couldn't even tell when the
system was turned on.
In the present study, patients
undergo the four-hour procedure, under general anesthesia,
described above. When the system is switched on, a continuous
high-frequency current flows into the electrodes. "The
current disrupts the seizure, but nothing else," explains
Dr Labar in a telephone interview.
FLIP
THE SEIZURE SWITCH
Adults with partial-onset epilepsy who've failed to
get a response from at least three AEDs and who have
at least six seizures per month are eligible to take
part in the study. "Patients who have a lot of AED side
effects are also perfect candidates," adds Dr Labar.
In the double blind phase of the study, the study and
control groups get the implants but the system is turned
off in the controls. All patients continue their AEDs.
A longer followup — with systems turned on in everyone
— will be tacked on afterwards. Eventually, the
researchers hope to enroll 124 patients in 15 centres
in the United States and Canada, including one at Toronto
Western Hospital.
Although the latest results haven't
been published yet, Dr Labar is optimistic. "It looks
like it's working," he says. "We have results so far
from 20 patients. Half of them have improved with the
DBS treatment."
Side effects have been minor: slight
tingling in the face, and a single infection easily
controlled with antibiotics.
STIMULATING
TRIALS
Intercept isn't the only such device in use or being
tested. Other similar techniques for epilepsy are the
Vagal Nerve Stimulator which, unlike DBS, targets a
specific peripheral nerve (the vagus); it's available
(and covered by medicare) in a few Canadian centres.
Another implanted device, the Responsive Neurostimulation
System (RNS), currently in clinical trials, only sends
impulses when it detects an incipient seizure.
DBS is already approved in
Canada as well as in the US, Europe and Australia for
treating Parkinson's disease and essential tremor. It's
also being tested, with some remarkable successes, in
the
treatment of severe refractory major depression by a
research team headed by Dr Helen Mayberg of Emory University
in Atlanta and Dr Andres Lozano of Toronto Western Hospital
(their results appeared in the March 3 issue of Neuron).
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