Abstracts

Patients with idiopathic generalized epilepsies frequently have findings on routine electroencephalography (EEG) of generalized spikes or sharp waves, 3-Hz or faster spike and slow wave complexs and/or polyspikes. It is unclear whether magnetoencephalography (MEG) would allow for lateralization and localization of these epileptiform discharges. We analyzed the results of MEG studies in 3 patients with medically refractory epilepsy whose history, examinations, and EEG findings were consistent with idiopathic generalized epilepsy, and whose brain magnetic resonance imaging studies (MRI) were normal. Simultaneous EEG-MEG recordings were conducted using a standard 10/20 electrode placement system and a 248-channel MEG gradiometer system (4-D Neuroimaging, San Diego, CA). The MEG-EEG recordings were visually inspected. Sources of MEG activity corresponding to the beginning of the generalized epileptiform interictal discharges were modeled as single equivalent current dipoles and projected onto the corresponding patient MRI studies. In all three patients, interictal EEG revealed bilateral synchronous epileptiform discharges without lateralization. Using MEG, the locations of sources that could be reliably estimated from the beginning of these events were found to regularly arise from regions within the right frontal lobe in two of the patients, and within the right parietal lobe in the third. In patients with idiopathic generalized epilepsies who have normal brain imaging studies, MEG can lateralize and localize sources for epileptiform discharges that appear bilateral and synchronous on EEG.