Page 463 - ILAE_Lectures_2015

Stimulation
Since the introduction of deep brain stimulation there has been a continuing quest to
determine its efficacy in the management of epilepsy. The numbers of patients who have
undergone deep brain and cerebellar stimulation for epilepsy are small and results to date
have not been dramatic. However, with the continuing advancements in stimulator
technology and the improved accuracy of implanting electrodes, this may be a continuing
source of development in the future. A recently reported randomised trial of the anterior
nucleus of the thalamus has shown efficacy comparable with vagal nerve stimulation (VNS).

Peripheral stimulation in the form of VNS has attracted considerable interest since it received
FDA approval in the United States in 1997 and is used as a palliative procedure in patients
for whom resective surgery is not suitable. Although not wholly elucidated, the
pathophysiological basis of periodic vagal nerve stimulation seems to be stimulation of
autonomic nervous pathways. Besides intermittent stimulation, on demand stimulation can
be achieved by the patient or companion.

At surgery the left vagal nerve is used in order to avoid cardiac side effects, and the electrode
is placed on the nerve in the neck between the common carotid artery and the internal jugular
vein. Side effects include hoarseness and coughing during stimulation and discomfort in the
neck. The median reduction of seizures from vagal nerve stimulation is 45% at one year.
While relatively few patients become seizure free with VNS, there are suggestions that
efficacy and quality of life further improve over time. An extensive patient registry and
ongoing clinical evaluation to provide a growing database of information will ultimately
allow a cost:benefit analysis of this therapy.

Multiple subpial transection
This technique was first described following animal research by Morel in which he
demonstrated that superficial incisions in the cortex could reduce seizure propagation while
preserving function. This followed recognition that the anatomical organisation of the cortex
was vertically oriented, while spike propagation occurred horizontally. In addition,
intragriseal incisions in the cortex had been shown to preserve the vascular supply, thus
preserving function. A critical volume of cortex was also shown to be necessary for spike
generation.

Multiple subpial transection is a technique advocated for the palliation of seizure generation
and propagation within eloquent cortex, with the objective of maintaining anatomical
function while reducing epileptogenesis. It is frequently used in conjunction with wider
resections which makes an accurate assessment of outcome following multiple subpial
transection difficult. There are a few specific indications including Landau-Kleffner
syndrome in children in whom, following demonstration of a predominant epileptogenic
focus following a methohexitol suppression test, multiple subpial transection may result in
improvement in both language, communication and behaviour.

Exploratory and future techniques

Gamma knife surgery
Following on from the ‘proof of concept’ that selective procedures on the medial temporal
lobe could be effective in the surgical management of epilepsy, Regis has pioneered the
concept of creating a stereotactic radiosurgical lesion to the amygdala and hippocampus
instead of performing a resection. Increase in efficacy comparing doses of 20 and 24 Gy has
been demonstrated, with a two-year seizure-free outcome similar to resection reported in a
carefully selected cohort. The theoretical benefits are that the patient avoids an open surgical
procedure and that the psychological/psychiatric consequences may be less. These must be
balanced against the risk of post-procedure swelling, delay to seizure freedom, increase in