In VNS therapy, intermittent electrical stimulation
is delivered to the left vagus nerve, which has ascending
fibers with widespread connections to the limbic,
autonomic and reticular brain regions. The reduced
thalamic blood flow that is observed in VNS has
been proposed to underlie the mechanism for seizure
reduction.50
In addition to a number of retrospective studies,
efficacy for this treatment option has been demonstrated
in two randomized, placebo-controlled,
double-blind trials, which reported a median seizure
reduction of 24.5%–28.0% in the group receiving high
level VNS compared to just 6.1%–15.0% in patients
receiving low level VNS (P = 0.01 and P = 0.04,
respectively).51,52 The risks associated with implantation
of the VNS device are relatively low, with a
3%–5% chance of infection.53–55 Vocal cord dysfunction,
throat discomfort, change in voice quality and
sleep apnea can present post-operatively, and such
consequences should be discussed with the patient
when considering this treatment. An additional factor
that should be considered when planning VNS
therapy is that patients are usually unable to undergo
magnetic resonance imaging (MRI) after implantation,
since the changing magnetic