Comparison of dense array EEG with simultaneous intracranial EEG for Interictal spike detection and localization

doi:10.1016/j.eplepsyres.2011.09.007

Epilepsy Research

Volume 98, Issues 2–3, February 2012, Pages 166-173

https://doi.org/10.1016/j.eplepsyres.2011.09.007 Get rights and content

Summary

Purpose

To evaluate the clinical utility of dense array electroencephalography (dEEG) for the detection yield and localization of interictal spikes in mesial temporal lobe epilepsy.

Methods

We simultaneously recorded 256-channel dEEG and intracranial electroencephalography (icEEG) implanted over the lateral and mesial temporal lobe in patients with intractable epilepsy. We calculated the dEEG spike detection rate for mesial temporal spikes which were confirmed by icEEG and applied source estimation to dEEG to compare noninvasive localization to the invasive recordings.

Results

339 of 760 interictal spikes (45%) were detected by dEEG examining the 256-channel head surface array. The average icEEG amplitude of dEEG detectable spikes was 1083 μV, and that of dEEG undetectable spikes was 780 μV (P < 0.05). All spikes detected in dEEG were localized to the temporal lobe. 295 of 339 spikes (87%) were well localized in mesial temporal lobe, close to the position confirmed by subdural electrodes.

Significance

256-channel dEEG may provide more precise information for the localization of interictal epileptiform discharges than conventional EEG or MEG in patients with deep spike foci. 256-channel dEEG may be clinically useful in the presurgical work-up for epilepsy, providing accurate noninvasive guidance for the placement of intracranial electrodes.

Introduction

It is important to understand the inherent limitations of noninvasive MEG and dEEG in predicting the brain activity seen by icEEG. Several studies have examined MEG measures taken simultaneously with implanted icEEG recordings. Mikuni et al. (1997), Oishi et al. (2002) and Huiskamp et al. (2010) reported that MEG was less sensitive in detecting and accurate in localizing in mesial temporal lobe compared to lateral temporal or frontal lobe. However, Kaiboriboon et al. (2010) reported good success in localizing medial temporal spikes with MEG dipole analysis to the resected side in 13 of 19 patients.

Long-term monitoring with dEEG has recently become feasible, and dEEG recordings of seizure onset have shown good predictive ability for localization obtained by long-term monitoring ECoG (Holmes et al., 2010). Although interictal events do not invariably localize to the seizure onset zone, a number of studies have shown interictal source localization with dEEG to be useful in neurosurgical planning in epilepsy (Michel et al., 2004).

In order to establish the clinical usefulness of dEEG, it is important to evaluate the sensitivity and accuracy of dEEG source analysis. For this purpose, we compared 256-channel dEEG source analysis of interictal activity and simultaneously recorded ECoG which covered both the lateral and mesial temporal lobe.

We received approval for this study from Seirei Hamamatsu General Hospital Human Subject Committee and informed consent was obtained from all patients.

Section snippets

Patients

We studied seven patients, each of whom had suffered from intractable epilepsy for at least 2 years. Each was a surgical candidate and underwent a presurgical workup including conventional long-term EEG monitoring, magnetic resonance imaging (MRI), 125-Iomazenil (IMZ)-single-photon emission tomography (SPECT), 18-F fluorodeoxyglucose (FDG)-positron emission tomography (PET) and neuropsychological testing. Clinical informations for these patients are summarized in Table 1.

Intracranial EEG (icEEG) recording

For each patient, from

Dense array EEG spike detection

A total of 760 intracranial icEEG spikes was recorded from mesial temporal regions in the 30–40 min recordings. A total of 339 spikes (45%) were clearly distinguished from the background activity by inspection of the dEEG whole-head topoplot. With the dEEG reduced to at 19-channel 10-20 display, 169 spikes (22%) were detected (Figure 1, Figure 2). Spike detection rates in each patient ranged from 37 to 59% for dEEG and 16 to 27% for the downsampled 19-channel 10-20 display (Fig. 3A).

Number of involved subdural electrodes and detection rate

Fig. 3B

Dense array EEG spike detection

Mesial temporal spikes confirmed by icEEG were detected 45% in 256-channel dEEG and 22% in downsampled 19-channel 10-20 display. In comparison, Mikuni et al. (1997) reported that MEG detected 18% of mesial temporal spikes, and Oishi et al. (2002) reported that MEG detected 53% of lateral frontal spikes but only 26% of mesial temporal spikes. Huiskamp et al. (2010) also reported that only 28% of icEEG spikes in mesial temporal lobe were detected by MEG, whereas 70% of icEEG spikes in lateral

Conclusion

Our study demonstrates that 256-channel dEEG can reliably detect mesial temporal spikes and localize them reasonably accurately. The 256-channel dEEG may provide more precise information for the localization of interictal epileptiform discharges than conventional EEG or MEG in patients with deep spike foci and may be clinically useful in the presurgical work-up for epilepsy, improving accuracy in the placement of intracranial electrodes.

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Comparison of dense array EEG with simultaneous intracranial EEG for Interictal spike detection and localization

Summary

Purpose

Methods

Results

Significance

Introduction

Section snippets

Patients

Intracranial EEG (icEEG) recording

Dense array EEG spike detection

Number of involved subdural electrodes and detection rate

Dense array EEG spike detection

Conclusion

MEG and EEG in epilepsy

J. Clin. Neurophysiol.

Detection of epileptiform discharges on magnetoencephalography in comparison to invasive measurements

Comparison of subcortical, cortical and scalp activity using chronically indwelling electrodes in man

Electroencephalogr. Clin. Neurophysiol.

Non-invasive pre-surgical evaluation with EEG/MEG source analysis

Electroencephalogr. Clin. Neurophysiol.

Spatial spectra of scalp EEG and EMG from awake humans

Clin. Neurophysiol.

Dense array EEG and source analysis reveal spatiotemporal dynamics of epileptiform discharges

Epilepsia

Localization of extratemporal seizure with noninvasive dense-array EEG. Comparison with intracranial recordings

Pediatr. Neurosurg.

Comparing noninvasive dense array and intracranial electroencephalography for localization of seizures

Neurosurgery

Regional differences in the sensitivity of MEG for interictal spikes in epilepsy

Brain Topogr.

Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography

Epilepsia

Interictal MEG/MSI in intractable mesial temporal lobe epilepsy: spike yield and characterization

Clin. Neurophysiol.

Concordance between routine interictal magnetoencephalography and simultaneous scalp electroencephalography in a sample of patients with epilepsy

J. Clin. Neurophysiol.

The value of multichannel MEG and EEG in the presurgical evaluation of 70 epilepsy patients

Epilepsy Res.

Epileptic source localization with high density EEG: how many electrodes are needed?

Clin. Neurophysiol.

Propagation of interictalepileptiform activity can lead to erroneous source localizations: a 128-channel EEG mapping study

J. Clin. Neurophysiol.