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After 15 years of research
and clinical studies, vagus nerve stimulation (VNS)
was approved by the FDA in 1997 as an add-on therapy
for adults and children over 12 who have partial
seizures that resist control by other methods. The
therapy is designed to prevent seizures by sending
regular small pulses of electrical energy to the
brain via the vagus nerve, a large nerve in the
neck.
The electrical impulses are
delivered by a flat, round generator, about the
size of a silver dollar, which is surgically implanted
below the collarbone on the left side of the chest.
Similar to a pacemaker, it is
computer controlled and battery powered. Thin wires
(electrodes) are threaded under the skin and wound
around the left vagus nerve in the neck. The generator
is programmed by the health team to send a few seconds
of electrical energy to the vagus nerve every few
minutes 24 hours a day. (Typically 30 seconds of stimulation
followed by a five-minute interval of no stimulation.)
In addition, the patient can trigger the impulse by
passing a pocket magnet over the generator when he/she
feels a seizure coming on. This sends an additional
charge to the brain which may have the effect of stopping
the seizure. It is also possible to turn the device
off by holding the magnet over it, although this is
not generally recommended.
Surgical implantation is usually
done in a 1-3 hour procedure under general anesthesia
or a regional block. A small incision is made in
the chest & another small incision on the side
of the neck for the lead. Although complete seizure
control is seldom achieved, the majority of people
who have the VNS implant experience fewer seizures.
For some patients, VNS has resulted in less severe
or shorter seizures, improved postictal period,
better mood, improved alertness, memory and cognition
and /or fewer emergency room visits. In some its
effectiveness increases with time. Most patients
continue to take their antiepileptic drugs during
treatment.
Side effects include voice change
or hoarseness, throat discomfort, a feeling of shortness
of breath and cough. These side effects typically
occur only when stimulation is "ON" and
not during the "OFF" period.
VNS is not a cure and does not work
for everyone. According to physicians involved in
the clinical studies, one-third of patients experienced
a profound improvement in overall quality of life,
one-third experienced good improvement and one-third
experienced little or no improvement. Currently,
there is no way to determine which patients will
respond to VNS or how quickly a patient may respond
to therapy.
For more information on VNS,
check out the website for Cyberonics, http://www.cyberonics.com
, developers of the VNS implant.
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