Abstracts

Objective: To study interictal magnetoencephalography (MEG), ictal high frequency oscillations (HFOs) and intracranial ictal onset zone (IOZ) in older children with refractory epileptic spams., Five patients (4.5 [ndash] 14 years) with intractable epileptic spasms (defined as per the proposed ILAE classification, 2001) who underwent surgery following intracranial EEG monitoring were studied for the clinical profiles, MRI, scalp and intracranial EEG, and MEG findings. MEG dipoles were marked on the exposed cortical surface using intraoperative neuronavigation system before subdural grid placement. We defined IOZ as low amplitude fast waves with or without slow waves before and during epileptic spasms. We compared location, distribution and frequency of HFOs (1000 Hz sampling rate) using multiple band frequency analysis (MBFA) and clustered MEG dipoles. Cortical resection area included IOZ, rapid ictal propagation area, prominent interictal zone, and clustered MEG dipoles., Seizure onset ranged 0.7-8 years. Three had asymmetrical spasms. Ictal scalp EEG showed generalized high amplitude slow waves with superimposed fast activities in four, including the one with following electrodecrement, and hemispheric electrodecrement alone in one. MRI showed normal findings in three, periventricular heterotopia and hemispheric ploymicrogyria in one each. MEG showed distinct clusters in four and a small cluster within diffuse scattered dipoles in one. IOZ was localized within the area of MEG cluster in four. Major portion of the ictal onset zone coincided with the area of MEG cluster in the other. Ictal HFOs ranging 150-258 Hz were located within the MEG cluster in four. Three patients became seizure free and one patient had [gt]90% reduction in seizure frequency. In the remaining one patient with residual seizures, ictal HFOs rapidly spread beyond MEG scattered dipoles. Limited cortical resection did not decrease the frequency of her epileptic spasms., Area of MEG dipole clusters contained the IOZ in older children with epileptic spasms. Intracranial EEG with subdural electrodes covering the area of MEG dipole clusters succeeded in identifying the IOZ and the delineation of the epileptogenic zone in epileptic spasms. Cortical ictal HFOs initiating epileptic spasms indicate that a subset of epileptic spasms represents focal onset seizures and may be classified as localization-related epilepsy.,