Abstracts

To evaluate the involvement of subcortical structures and cerebellum during focal and generalized interictal epileptic discharges, using the blood oxygenation level-dependent (BOLD) effect. We used the EEG-functional MRI method to measure the BOLD effect during interictal epileptic discharges. We selected studies that showed BOLD responses to compose two groups: patients with focal discharges or with generalized spike and wave activity (GSW). The t-stat maps were analyzed to determine the presence of activation (positive BOLD) and deactivation (negative BOLD) in thalamus, basal ganglia, brain stem and cerebellum. Focal group included 14 patients, (mean age of 35 years, range = 22-57), with a mean age at onset of epilepsy of 18 years (range = 5-37 years). GSW group included 15 patients with normal MRI (mean age of 35 years, range = 18-66) and a mean age at onset of epilepsy of 11 years (range = 3-24). In accordance with inclusion criteria, a cortical response was observed in all focal (n=18) and GSW (n=18) studies. Thirty-two (89%) studies showed subcortical and cerebellar responses, 16 in each group. Focal discharges caused more circumscribed fMRI responses than GSW. Activation, deactivation or both, were found in all structures and with an equal frequency except for thalamus where a response was more likely during GSW. The frequency of responses in each structure was: thalamus in 6/18 focal studies (33%) versus 11/18 GSW studies (61%); basal ganglia in 9/18 focal (50%) versus 12/18 GSW (67%); in brain stem 6/18 focal (33%) versus 5/18 GSW (28%); and in cerebellum 13/18 in both (72%). Activations were less frequent in the thalamus during focal discharges compared to GSW, but tended to occur more often in the other structures particularly brain stem and cerebellum. Deactivations occurred more frequently in all structures, except brain stem, during GSW compared to focal discharges. During focal discharges, responses in thalamus and basal ganglia could be either uni-, contra- or bilateral, but were mostly bilateral in the cerebellum. During GSW, responses clearly tended to be bilateral in thalamus, basal ganglia and cerebellum. The responses in the brain stem were not lateralized. This study shows that the thalamus, basal ganglia, brainstem and the cerebellum are metabolically active during focal and generalized interictal epileptic discharges. The thalamus and basal ganglia appear to be more involved during GSW, while the cerebellum is frequently involved in both types of epileptic activity. EEG-fMRI is a non-invasive, repeatable, method that can disclose diffuse abnormalities at the time of interictal epileptic discharges, highlighting the relationship between cortical and subcortical structures in epilepsy. (Supported by Canadian Institutes of Health Research.)