Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography.
OBJECTIVE
Objectively to evaluate whether independent spike detection by human interpreters is clinically valid in magnetoencephalography (MEG) and to characterize detection differences between MEG and scalp electroencephalography (EEG).


METHODS
We simultaneously recorded scalp EEG and MEG data from 43 patients with intractable focal epilepsy. Raw EEG and MEG waveforms were reviewed independently by two experienced epileptologists, one for EEG and one for MEG, blinded to the other modality and to the clinical information. The number and localization of spikes detected by EEG and/or MEG were compared in relation to clinical diagnosis based on postoperative seizure freedom.


RESULTS
Interictal spikes were captured in both EEG and MEG in 31, in MEG alone in eight, in EEG alone in one, and in neither modality in three patients. The number of detections ranged widely with no statistical difference between modalities. A median of 25.7% of total spikes was detectable by both modalities. Spike localization was similarly consistent with the epilepsy diagnosis in 85.2% (EEG) and 78.1% (MEG) of the patients. Inaccurate localization occurred only in those cases with very few spikes detected, especially when the detections were in one modality alone.


CONCLUSIONS
Interictal epileptiform discharges are easily perceived in MEG. Independent spike identification in MEG can provide clinical results comparable, but not superior, to EEG. Many spikes were seen in only one modality or the other; therefore the use of both EEG and MEG may provide additional information.
Iwasaki
Masaki
M
Department of Neurology, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Pestana
Elia
E
Burgess
Richard C
RC
Lüders
Hans O
HO
Shamoto
Hiroshi
H
Nakasato
Nobukazu
N
D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods; D002540:Cerebral Cortex / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D003627:Data Interpretation, Statistical; D003936:Diagnosis, Computer-Assisted / Q000706:statistics & numerical data; D004569:Electroencephalography / Q000706:statistics & numerical data*; D004828:Epilepsies, Partial / Q000175:diagnosis; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D015225:Magnetoencephalography / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012107:Research Design; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric