Abstracts

Rationale: Simultaneous recording of interictal EEG and fMRI is increasingly used to provide information about the irritative and epileptogenic zones in focal epilepsy and studies suggest 60% of patients have IED correlated BOLD activation concordant with seizure onset. FMRI of seizures is much more difficult to obtain and interpret, but case reports suggest it may provide useful insight into the neurobiology of the epileptic network (1,2). We aimed to study ictal EEG-fMRI in a group of patients with focal epilepsy, focussing not only on cortical activations, but BOLD signal change in sub-cortical structures. Methods: 71 patients with focal epilepsy currently awaiting intracranial recording were selected for study with EEG-fMRI. All underwent structural MRI and video-EEG for seizure localisation. Forty-minute EEG-fMRI recordings were performed at 3T with 32-channel EEG. Interictal discharges, electrographic seizure onset, ictal discharges and post-ictal EEG changes were identified seperately and used to model BOLD signal changes in the same general linear model (GLM) in SPM5. The spatial pattern of BOLD signal change correlated with each was recorded and also compared with intracranial data where available. Results: 9/71 patients had seizures during scanning. 6 patients had frontal lobe epilepsy, 2 had temporal lobe epilepsy and 1 had posterior epilepsy. 7/9 had more than one seizure during the session (range 2-6). Interictal discharges were recorded in 5 patients. IED correlated BOLD signal change was concordant with the putative irritative zone in 4/5 patients. In the remaining subject, no IED-correlated BOLD signal change was observed. BOLD signal change related to electrographic seizure onset was concordant with the seizure onset zone in 5/9 patient, but was more extensive than that observed in the interictal data with more remote regions involved. It was discordant in two and there was no change in two. Seizure onset has been confirmed on intracranial recording in 4 of the 9 patients. Post-ictal EEG changes were associated with negative BOLD signal change in the contralateral cortex in 4/9 patients and with BOLD signal change in sub-cortical structures (putamen, caudate and/or thalamus) in 5/9 patients. Conclusions: These results suggest combined interictal and ictal EEG-fMRI, in addition to providing valuable localising information, is a useful technique for the dynamic non-invasive study of seizures in focal epilepsy. This work was undertaken at UCLH/UCL who received a proportion of funding from the Department of Health’s NIHR Biomedical Research Centres funding scheme and Supported by a grant from the UK Medical Research Council no.G0301067. We are grateful to the Big Lottery Fund, Wolfson Trust and National Society for Epilepsy for supporting the NSE MRI scanner.