Abstracts

Magnetoencephalography (MEG) has been increasingly used in patients with intractable localization-related epilepsy. The accuracy of MEG source localizations onto MRI depends upon the ability of patients to keep still in the dewar. Thus, uncooperative children with epilepsy require general anesthesia (GA) for the MEG and MRI studies. GA has been known to either eliminate or provoke epileptic discharges. We evaluated MEG and simultaneous EEG spikes under GA in young children with intractable epilepsy in comparison with prolonged video-EEG (VEEG) results. A total of 185 pediatric patients with epilepsy underwent MEG study with simultaneous 19-channel scalp-EEG at The Hospital for Sick Children in Toronto. These patients also had VEEG for 16-96 hours with 19-scalp electrodes. Twenty-one of 185 children (11%) underwent GA for MEG and MRI studies. Propofol and remifentanil were used for GA. Whole-head 151-channel gradiometers were used for MEG recording (VSM MedTech Ltd., Port Coquitlam, BC, Canada). We performed MEG dipole analysis using single moving dipole modeling. We compared MEG spikes and dipoles with interictal spikes of VEEG and simultaneous EEG. We studied twenty-one children consisting of 10 girls and 11 boys. Age at time of MEG study ranged between 7 months and 9 years (mean [plusmn] SD, 4.7 [plusmn] 2.6 years). Age of seizure onset ranged from one day of life to 3 1/2 years (0.9 [plusmn] 1.0 years). Eighteen children had MRI abnormalities. There was a positive correlation among number of MEG dipoles, number of interictal epileptiform discharges per minute on VEEG and number of EEG spikes under GA. The more frequent spikes VEEG showed, the more frequent EEG spikes and MEG dipoles we obtained under GA. Fifteen patients showed [ge] 10 MEG dipoles. Their VEEG findings were as follows. Three patients had regional interictal epileptiform discharges, 5 had hemispheric, 2 had bilateral, 4 had multiple, and one with no interictal epileptiform discharges. Six patients showed [lt] 10 MEG dipoles. Their VEEG findings consisted of bilateral and generalized discharges in 4 patients, generalized or bilateral interictal epileptiform discharges in one each. MEG under GA is a useful procedure to perform in young children with frequent focal epileptiform discharges during VEEG. The patients with generalized interictal epileptiform discharges on VEEG did not provide sufficient MEG dipoles because the generalized interictal epileptiform discharges disappeared under GA.