Magnetoencephalographic and electroencephalographic evaluation in patients with cryptogenetic partial epilepsy

Clinical Analysis of Partial Epilepsy with Auras

Background:

An aura is usually considered to be the initial clinical sign of a seizure. The types of abnormal neuron activities (i.e., localized and generalized firing) play an important role in the diagnosis of epilepsy. The goal of this study was to investigate the types of auras and its correlation with the localization and treatment of epilepsy.

Methods:

The 426 epileptic patients with auras from a single center were reviewed with reference to International League Against Epilepsy (ILAE, 1981) classification; the clinical manifestations and incidence of auras were analyzed in this retrospective study, as well as the results of electroencephalogram (EEG), brain magnetic resonance imaging (MRI) and the treatment methods.

Results:

Among the 426 epileptic patients, six different types of auras were defined, including autonomic auras, sensory auras, mental and affective auras, aura as vertigo, cognitive auras, and unspeakable feelings. Duration of auras ranged from 2 s to 7 min; the median duration of auras was 64.2 s. Abnormal EEG was observed in 297 (69.72%) patients. Moreover, abnormal brain MRI was observed in 125 (29.34%) patients. Nineteen (4.46%) epilepsy patients with auras underwent both surgeries and antiepileptic drugs (AEDs) while others were treated only with AEDs.

Conclusions:

This study suggested that auras played an important role in the diagnosis, classification, and localization of epilepsy. Epileptic aura could help differentiate partial seizure from generalized seizure.

Magnetoencephalography and magnetic source imaging in epilepsy

Magnetoencephalograpy (MEG) and Electroencephalography (EEG) provide physicians with complementary data and should not be regarded as mutually exclusive evaluative methods of cerebral activity. Relevant to this edition, MEG applications related to the surgical treatment of epilepsy will be discussed exclusively. Combined MEG/EEG data collection and analysis should be a routine diagnostic practice for patients who are still suffering seizures due to the failure of drug therapy. Clinicians in the field of epilepsy agree that a greater number of patients would benefit from surgery than are currently referred for pre-surgical evaluation. Regardless of age or presumed epilepsy syndrome, all patients deserve the possibility of living seizure-free through surgery. Technological advances in superconducting elements as well as the digital revolution were necessary for the development of MEG into a clinically valuable diagnostic tool. Compared to the examination of electrical activity of the brain, investigation into its magnetic concomitant is a more recent development. In MEG, cerebral magnetic activity is recorded using magnetometer or gradiometer whole-head systems. MEG spikes usually have a shorter duration and a steeper ascending slope than EEG spikes, and variable phase relationships to EEG. When co-registered spikes are compared, it is apparent that EEG and MEG spikes differ. There is agreement among investigators that more interictal epileptiform spikes are seen in MEG than EEG. When MEG is co-registered with invasive intracranial EEG data, the detection rate of interictal epileptiform discharges depends on the number of electrocorticographic channels that record a spike. When patients have a non-localizing video-EEG recording, MEG pinpoints the resected area in 58-72% of the cases.

Spike orientation may predict epileptogenic side across cerebral sulci containing the estimated equivalent dipole

OBJECTIVE

To evaluate whether the orientation of interictal spikes, localized in major sulci by magnetoencephalography (MEG), predicts the epileptogenic side of the sulcal wall.

METHODS

Sixteen epilepsy patients were analyzed in whom equivalent current dipoles (ECDs) of MEG spikes were localized on the central (four patients), interhemispheric (4), or sylvian fissure (8); and the epileptogenic side across the sulci had been confirmed by seizure semiology, structural lesions, or intracranial electroencephalography (EEG). ECD was classified as epileptogenic side or normal side oriented and correlated to the scalp EEG map.

RESULTS

All central (n=50) and interhemispheric (n=83) spike ECDs were oriented toward the epileptogenic side at peak latency. In scalp EEG, 91% of the spikes showed radial pattern of broad negativity above the sulcus whereas 9% showed tangential pattern with positive maximum above the epileptogenic side. Sylvian spikes were only found in patients with temporal lobe epilepsy (TLE). In sylvian spikes (n=220), 73% of ECDs were oriented toward the epileptogenic side, whereas 27% were oriented toward the normal side.

CONCLUSIONS

In central and interhemispheric spikes, epileptogenic side cortex may be gross surface negative through the sulcal wall to the adjacent gyrus. Inconsistent orientation of the sylvian spikes suggests a complex pattern of spike propagation in TLE.

SIGNIFICANCE

ECD orientation of central and interhemispheric spikes in MEG may predict the epileptogenic side.

Revisiting the role of magnetoencephalography in epilepsy

PURPOSE OF REVIEW

This review considers the current role of magnetoencephalography in clinical epileptology.

RECENT FINDINGS

While magnetoencephalography and electroencephalography complement each other for interictal spike detection, magnetoencephalography is more sensitive in neocortical epilepsy. In temporal lobe epilepsy, magnetoencephalography can attribute epileptic activity to subcompartments of the temporal lobe and differentiate between patients with mesial, lateral and diffuse seizure onsets. In extratemporal epilepsy, magnetoencephalography provides unique information in nonlesional cases and helps to define the relationship of epileptic activity with respect to lesions and eloquent cortex. Magnetoencephalography also contributes to the clinical decision process in patients with cortical dysplasias, Landau-Kleffner syndrome and recurrent seizures after prior epilepsy surgery. Magnetoencephalography-guided re-evaluation of magnetic resonance imaging helps to reveal previously unrecognized lesions. In a presurgical setting interictal magnetoencephalography was superior to scalp electroencephalography. Complete resection of the magnetoencephalography-defined irritative zone has prognostic implications on postoperative seizure control. Magnetoencephalography can reliably localize sensorimotor and language cortex. Disadvantages of this technique include the difficulties in obtaining ictal recordings and the considerable costs involved.

SUMMARY

Magnetoencephalography has been developed to a valuable noninvasive tool in clinical epileptology. The development of approaches which take into account both magnetoencephalography and electroencephalography simultaneously should provide more useful information in the future.