Epileptic spikes: magnetoencephalography versus simultaneous electrocorticography.
OBJECTIVE
To test the sensitivity of extracranial magnetoencephalography (MEG) for epileptic spikes in different cerebral sites.


METHODS
We simultaneously recorded MEG and electrocorticography (ECoG) by using subdural electrodes with 1-cm interelectrode distances for one patient with lateral frontal epilepsy and one patient with basal temporal epilepsy. We analyzed MEG spikes associated with ECoG spikes and compared the maximal amplitude and number of electrodes involved. We estimated and evaluated the locations and moments of the equivalent current dipoles (ECDs) of MEG spikes.


RESULTS
In patient 1, MEG detected 100 (53%) of 188 ECoG lateral frontal spikes, including 31 (46%) of 67 spikes that activated three subdural electrodes. MEG spike amplitudes correlated with ECoG spike amplitudes and the number of electrodes activated (p < 0.01). ECDs were perpendicular to the superior frontal sulcus. In patient 2, MEG detected 31 (26%) of 121 ECoG basal temporal spikes, but none that activated only three subdural electrodes. ECDs were localized in the entorhinal and parahippocampal gyri, oriented perpendicular to those basal temporal cortical surfaces. The ECD strength was 136.6 +/- 71.5 nAm in the frontal region, but 274.5 +/- 150.6 nAm in the temporal region (p < 0.01).


CONCLUSIONS
When lateral frontal ECoG spikes extend >3 cm2 across the fissure, MEG can detect >50%, correlating with spatial activation and voltage. In the basal temporal region, MEG requires higher-amplitude discharges over a more extensive area. MEG shows a significantly higher sensitivity to lateral convexity epileptic discharges than to discharges in isolated deep basal temporal regions.
Oishi
Makoto
M
Departments of Neurosurgery, National Nishi-Niigata Central Hospital, and Brain Research Institute, Niigata University, Niigata, Japan. oishi@masa.go.jp
Otsubo
Hiroshi
H
Kameyama
Shigeki
S
Morota
Nobuhito
N
Masuda
Hiroshi
H
Kitayama
Masaomi
M
Tanaka
Ryuichi
R
D000328:Adult; D002540:Cerebral Cortex / Q000503:physiopathology*; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis*; D005500:Follow-Up Studies; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D012680:Sensitivity and Specificity