SY6.3. MEG in epilepsy: Established tool or research topic?

Abstract

Both electroencephalography (EEG) and magnetoencephalography (MEG) measure the same underlying brain activities. The greatest advantage of MEG is that source estimation techniques are easier to apply for MEG than for EEG. Thus, MEG is one of the best ways to assess the brain activity in patients with epilepsy, because it is noninvasive and can be used multiple times for the same patient. Magnetic source imaging (MSI) of interictal spikes as part of presurgical evaluations is one of the most successful clinical applications of MEG. A single tight cluster of MEG spike dipoles is well correlated with ictal onset zone. Conventional EEG analysis is not always able to define the epileptogenic area. To this end, the single-dipole analysis tools can resolve localized epileptic MEG discharges and demonstrate equivalent current dipoles (ECDs) in cerebral cortex. Epileptic spikes arose from the mesial temporal lobe epilepsy are sometimes not estimated by MSI. However, MEG-positive spikes with EEG-negative spikes are often found by MEG. Jerk-locked back averaging of the myoclonic discharges in a patient with epilepsia partialis continua is useful for the precise location of the epileptogenic zone. In this talk, an overview on MEG for epilepsy will be presented. Then, minimum norm estimates and beamformer analysis will be introduced. These methods are sometimes beneficial for determining the propagation of epileptic discharges and the epileptic activities located in the deep structures. I will also introduce the concept that hippocampal sclerosis modulates the central auditory processing (CAP) in patients with mesial temporal lobe epilepsy (mTLE). CAP dysfunction provides us information on the lateralization of mTLE. Especially, altered neural synchronization may provide useful information about possible functional deterioration in patients with unilateral mTLE. In conclusion, MEG is useful for the diagnosis of epilepsy. It also provides us an insight into the pathophysiology of epilepsy.