Abstracts

Seizures are very common among individuals with tuberous sclerosis complex (TSC) and are often medically intractable. Epileptogenic lesions of tuberous sclerosis are the result of a complex developmental disorder of neuronal migration including cortical/subcortical tubers and areas of cortical dysplasia. As most patients with TSC have multiple potentially epileptogenic tubers and interictal scalp EEG often reveals multifocal epileptic discharges, epilepsy surgery is often discouraged. Magnetoencephalography (MEG) provides an additional tool for localization of interictal epileptiform discharges and is able to more precisely localize spike sources than scalp EEG. The primary goal of this study is to characterize MEG spike sources (MEGSS) in TSC as part of presurgical evaluation and to examine the correlations and possible divergence between MEG, EEG and MRI in TSC. We studied seven children with TSC and intractable epilepsy. Age at MEG study ranged from 43 months to 12 years and duration of epilepsy ranged from 3-11 years. As part of presurgical evaluation, all patients underwent prolonged scalp Video-EEG monitoring, EEG single moving dipole analysis, 151 channels MEG with single moving dipole modeling and brain MRI. We defined MEGSS distribution as a cluster of [ge] 6 dipoles with less than 1 cm apart, and a scatter of [lt] 6 dipoles or more than 1 cm apart. We compared MEGSS distribution to interictal and ictal EEG findings, EEG dipole distribution and MRI. Four patients had one or more MEGSS clusters, and all patients had scattered MEGSS. The MEG distribution patterns were classified into three groups. Group A in two patients with unilateral single cluster, Group B in two patients with bilateral clusters and group C in three patients with bilateral scattered MEGSS and no clusters. Both patients in group A had a single MEG cluster that was concordant with a single epileptic region determined by EEG dipoles and ictal onset zone and a prominent tuber on MRI. Patients in group B and C had divergent epileptic regions between MEG, EEG and MRI. This study provides evidence for the potential value of MEG in the presurgical evaluation of intractable epilepsy in TSC. A single MEG cluster that correlates to the interictal EEG dipole lateralization, ictal onset zone and the prominent tuber on MRI indicates a simple epilepsy network that can be surgically managed for optimal seizure control. Bilateral MEG clusters and scattered MEG dipoles with multiple tubers on MRI indicate a more complex epilepsy network involving both hemispheres.