Developments in Neurostimulation Therapy for Epilepsy
Developments in Neurostimulation Therapy for Epilepsy
European Neurological Review, 2009;4(2):88-90
US Neurology, 2010;5(2):78-81
Abstract
Neuromodulating neural tissue instead of performing lesions is a current trend in neurosurgery. In the case of epilepsy, stimulation of the nervous system is under investigation, and the field is growing at a fast pace. The purpose of this article is to review the various targets that have been studied in the search for a way to control refractory seizures. Consideration is made of why each target is chosen, patient selection, results, and adverse effects. Cerebellar stimulation was the first proposed method; vagus nerve stimulation is currently the most widely used due to its easy technique, but the results on seizure reduction are modest. Other targets were chosen with the idea of interfering with seizure propagation—this is the case with thalamic stimulation. Currently, studies are being performed stimulating the epileptic focus. Although there are still many controversies regarding which is the best target and stimulating parameters, all authors agree that neuromodulation reduces seizures and has the advantage of being reversible and safe.
Keywords
Neuromodulation, electrical brain stimulation, epilepsy, refractory seizures, stimulation anatomical targets, epilepsy surgery
Disclosure: The author has no conflicts of interest to declare.
Received: January 5, 2009 Accepted: May 11, 2009
Correspondence: Ana Luisa Velasco, MD, PhD, Cerrada Bosques de Moctezuma 55, La Herradura, Huixquilucan, Estado de México, 52784, Mexico. E: analuisav@yahoo.com
It is estimated that epilepsy affects approximately 50 million people worldwide.1 Although conventional antiepileptic medications as well as newly developed ones have improved response in the majority of patients, it is known that up to 30% do not respond to appropriate therapy no matter how many antiepileptic drugs are administered.2 These non-responsive patients are candidates for epilepsy surgery.
Many ablative procedures have been used, with differing results. Some procedures have excellent results, such as temporal lobectomy for mesial temporal epilepsy; others, such as callosotomy for generalized seizures or frontal resections for motor seizures, have poor results. Regardless of which procedure we choose, there are a number of patients who are not candidates for resective surgery due to several factors: poor seizure outcome with the chosen surgical procedure, failure to localize precise epileptic focus, bilateral or multiple foci, and high risk for post-surgical neurological deficits. In these circumstances patients are either excluded from surgery or surgery is performed partially with the risks of function loss and seizure persistence.
Brain stimulation has been proposed as an alternative surgical procedure that prevents resection of neural tissue. Instead of being removed or disconnected, tissue is stimulated in a programmed mode and ‘taught’ not to seize. For this purpose, special electrodes are used that are directed to different targets (for example the thalamus, cerebellum, or hippocampus). They are designed to remain within the stimulated target permanently. They are connected through a subcutaneous extension to a subcutaneous pulse generator, which produces current that is delivered to the chosen target. With a portable computer we can turn the generator on or off, program it, choose the stimulation parameters (amplitude, frequency, pulse width, and other parameters), and change the stimulated contacts if desired. It is a reversible method.
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Neuromodulation, electrical brain stimulation, epilepsy, refractory seizures, stimulation anatomical targets, epilepsy surgery, epilepsy treatment, epilepsy diagnosis, epilepsy symptoms,
