Tohoku J. Exp. Med., 2004, 203(3)

Comparison of Magnetoencephalographic Spikes with and without Concurrent Electroencephalographic Spikes in Extratemporal Epilepsy

HYEON-MI PARK, NOBUKAZU NAKASATO,¹ MASAKI IWASAKI,² HIROSHI SHAMOTO,¹ TEIJI TOMINAGA² and TAKASHI YOSHIMOTO²

Department of Neurology, Gil Medical Center, Gachon Medical School, Inchon, Korea,
¹Department of Neurosurgery, Kohnan Hospital, Sendai 982-8523, and
²Department of Neurosurgery, Tohoku University Graduate School of Medicine, Sendai 980-8574

Interictal spikes in patients with epilepsy may be detected by either electroencephalography (EEG) (E-spikes) or magnetoencephalography (MEG) (M-spikes), or both MEG and EEG (E/M-spikes). Localization and amplitude were compared between E/M-spikes and M-spikes in 7 adult patients with extratemporal epilepsy to evaluate the clinical significance of MEG spikes. MEG and EEG were simultaneously measured using a helmet-shaped MEG system with planar-type gradiometers and scalp electrodes of the international 10-20 system. Sources of E/M-spikes and M-spikes were estimated by an equivalent current dipole (ECD) model for MEG at peak latency. Each subject showed 9 to 20 (mean 13.4) E/M-spikes and 9 to 31 (mean 16.3) M-spikes. No subjects showed significant differences in the ECD locations between E/M- and M-spikes. ECD moments of the E/M-spikes were significantly larger in 2 patients and not significantly different in the other 5 patients. The similar localizations of E/M-spikes and M-spikes suggest that combination of MEG and EEG is useful to detect more interictal spikes in patients with extratemporal epilepsy. The smaller tendency of ECD amplitude of the M-spikes than E/M-spikes suggests that scalp EEG may overlook small tangential spikes due to background brain noise. Localization value of M-spikes is clinically equivalent to that of E/M-spikes.

keywords —— magnetoencephalography; electroencephalography; epilepsy; interictal spike; equivalent current dipole

© 2004 Tohoku University Medical Press

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Address for reprints: Nobukazu Nakasato, M.D., Ph.D., Department of Neurosurgery, Kohnan Hospital, 4-20-1 Nagamachi-minami, Taihaku-ku, Sendai 982-8523, Japan.

e-mail: nak@kohnan-sendai.or.jp