Abstracts

Rationale: Idiopathic generalized epilepsy (IGE) is characterized by generalized tonic-clonic, absence and/or myoclonic seizures. Although traditionally these seizure types were hypothesized to arise from subcortical structures resulting in the classic, generalized spike and wave patterns, analyses of epileptiform discharges utilizing source localization algorithms suggest that some generalized seizure types may arise from cortical sources with very rapid, diffuse propagation of the ictal activity. Gross lesions are not present on magnetic resonance imaging (MRI) or neuropathologic examinations; however malformations of cortical development have been identified and characterized in some patients with IGE. Previous quantitative analyses of MRI in patients with IGE have identified subcortical and cortical differences when compared to normal controls. We hypothesized that quantitative assessments of cortical thickness and subcortical volumes will identify subtle structural differences between patients with IGE and normal controls. Methods: T1-weigthed MRIs optimized for gray-white matter contrast were obtained for 14 patients with IGE and 14 age and sex matched controls. Automated cortical surface reconstruction and sub-cortical segmentation were performed utilizing FreeSurfer. Registration and averaging of the groups was performed for vertex-wise comparison of cortical thickness between controls and IGE patients; correction for multiple comparisons was done utilizing cluster-based thresholding. Results: The mean age for IGE patients was 37.0 years (median: 35.9, range: 21.5 to 50.4); the mean age for normal controls was 37.9 years (median: 36.9, range 22.7 to 51.1). Five patients had only generalized tonic-clonic seizures, two patients had only myoclonic seizures. Three patients had myoclonic seizures and tonic-clonic seizures and four patients had absence seizures, myoclonic seizures and tonic-clonic seizures. Univariate analyses of subcortical volumes demonstrated increased thalamic volume among IGE patients. Analyses of cortical thickness revealed group differences between IGE and normal controls with regions of thickening as well as thinning identified. Conclusions: Our findings identify quantitative MRI differences in both cortical and subcortical regions associated with IGE.