Detection of epileptic spikes by magnetoencephalography and electroencephalography after sleep deprivation

Abstract

Introduction:In diagnosis of epilepsies electrophysiological findings play a key role. While spontaneous electroencephalography (EEG) and EEG with sleep deprivation (EEGsd) are widely evaluated and used, application of magnetoencephalography (MEG) in this field is primarily limited to presurgical assessment of focal epilepsies. Methods: In this study we retrospectively compared MEG (M/EEG) and EEGsd in 63 (55) patients with focal and generalized epilepsy with regard to occurrence of epileptic spikes. Results: MEG could record epileptic spikes in 38 patients (60%), while EEGsd recorded spikes in only 32 patients (51%). In a group of 55 patients simultaneous MEG/EEG (M/EEG) was able to record spikes in 38 patients (71%) compared to epileptic spikes in 28 patients (51%) recorded by EEGsd. In a subgroup of 17 MR-negative patients simultaneous M/EEG could record epileptic spikes in all patients, while EEGsd was successful in only 11 (64%) of them. Conclusion: In this study, MEG showed a tendency to record epileptic spikes in more patients than EEGsd. Furthermore, simultaneous M/EEG has been shown to be especially successful in detection of epileptic spikes in patients with MR-negative epilepsy. This might at least in parts be explained by neocortical predominance of MR-negative epilepsy. Thus, this study motivates prospective studies to evaluate the substitutability of EEGsd by MEG more extensively.

Latency of interictal epileptiform discharges in long-term EEG recordings in epilepsy patients

“…First, we did not find IEDs in 21.4% of patients. It may be obvious that the EEG sensitivity can be increased by longer or repeated EEG recordings, as well as simultaneous magnetencephalography (MEG)/EEG recording [6,10,25,27,[43][44][45]]. Yet, 21% of patients in our series did not have IEDs despite long-term EEG recordings and seizures.…”

Magnetoencephalography in the presurgical evaluation of epilepsy

“…If we explore the data from 173 patients with varying epilepsies from three large studies [47][48][49], 54% (93/173) of the patients had spikes on both EEG and MEG, 7% (12/173) had spikes only on the EEG, 18% (32/173) had spikes only on MEG, and 21% (36/173) did not have spike on either modality. We can use these numbers to calculate a statistic that is more important, given the usual sequence of EEG and MEG: almost half (47%, 32/68) of all patients who do not have spikes on EEG will have spikes on MEG.…”

“…No clear hypothesis regarding seizure onset MEG detects interictal spikes in about half of patients without EEG spikes [47][48][49]. MEG can detect insular spikes [16][17][18].…”

Preoperative evaluation and surgical decision-making in pediatric epilepsy surgery

“…First, MEG is more sensitive than EEG in detecting smaller epileptic foci, with a threshold of 4-8 vs. 10-15 cm 2 for scalp EEG (25). Interictal MEG epileptiform discharges, including activity from insular cortex (26)(27)(28), may be seen in approximately 50% of patients without detectable interictal epileptiform discharges on scalp EEG (29)(30)(31), which makes MEG particularly useful in guiding the placement of intracranial electrodes in patients without a structural lesion detectable by MRI. It is also advantageous compared with scalp EEG recordings for the detection and lateralization of interhemispheric epileptiform activity (32)(33)(34) and can detect interictal mesial temporal lobe discharges in as many as 85% of patients with mesial temporal lobe epilepsy (35).…”