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Vagus Nerve Schwannoma: effects on internal organs?

Jerry Larson jlarson at hsc.usc.edu
Fri Jan 26 20:42:50 EST 1996


> Moving in the other direction...  I have a student with rather bad
grande mal epilepsy.  .... He 
> is about to undergo a procedure to have an electrode implanted which
will stimulate the vagus 
> nerve.  ....Is this a reasonable procedure?  
> 
> Have any of you heard of this procedure?  If it works, why does it
work?  Why did someone 
> think to try it (i.e., what is the theoretical rationale)?



We have a vagus nerve stimulation program nere at USC.  It's still an
experimental procedure. (The study here is closed at this time, so they
can't take more subjects). Yes, it does seem to do some good in many
cases.
It isn't really known how it works, and I don't know how someone came to
think of it, but just to speculate a little, the vagus nerve projects to a
great many brain areas.  By stimulating it, you produced increased ordered
activity in large areas of the brain.  By ordered, I mean the neurons are
busy with their specifc tasks instead of being available to participate in
a seizure, which is kind of a disorderly mass or mob action on the part of
millions of neurons.
You might think, then, that by turning on the stimulator, a person could
prevent a seizure, and in fact some people who have auras (can tell when a
seizure is coming on) do use it this way.  The claim being made by the
manufacturer and tested in the study, though, is a little different: that
being stimulated several times a day reduces the frequency of seizures, as
if it were a drug.  I don't exactly know why that should work, but it
seems clear that it does in many cases.

The first option if you have seizures is medication, and you can try more
than one medication or combination of meds.  For some people who have
intractable seizures, surgery is the second option; for some people who
are not candidates for surgery, or who still have intractable seizures
even after surgery,the stimulator can help.



  What are the risks?  

Not really known, I'd guess, and that's one of the reasons it's being
studied.  What's involved is the implantation of a device in the chest
cavity, similar to a heart pacemaker.  It can be controlled by a magnet
outside the body, and can also be reprogrammed with an external device. 
The stimulating electrode itself is wrapped around the left vagus nerve. 
It's a fairly brief surgery, but it does involve working near the carotid
artery and is done under general anesthesia, so it has all the standard
risks of infection, stroke, etc.  Some people have a side effect of poor
voice quality or swallowing problems when the stimulator is actually on,
but this seems to be pretty minor.

My overall impression is that it's not a procedure with terrible risks or
side effects, and that it  can be of some benefit in reducing the number
of seizures.  The thing is, even a few seizures can be very debilitating,
so you really want something that will get rid of your seizures entirely,
but failing that, reducing the number, length and severity of seizures can
make a big difference.  I also think there are some individuals who can
feel a seizure coming on and prevent it by turning on their stimulator,
and for them it might be pretty close to curing the problem entirely. 
However, that isn't being claimed at this time.

Sorry I don't know more about it; within a few weeks I'll have a vagus
nerve page on the Web with more information, and I'll make sure to include
answers to your questions.  The URL will be (linked to) 
http://www.usc.edu/hsc/neuroprotection/
> 
Jerry



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