Abstracts

Rationale: : Near-infrared spectroscopy (NIRS) is a novel non-invasive imaging technique of potential value in the pre-surgical investigation of patients with refractory epilepsy. NIRS has been used to investigate language lateralization in epileptic patients [1], including children [2] showing good concordance with other techniques (Wada Test, functional magnetic resonance - fMRI). Moreover, preliminary NIRS studies with epileptic populations have shown an increase of regional cerebral blood volume (rCBV), total heamoglobin (HbT), and of oxy-heamoglobin (HbO) lateralized on the side of seizure onset during complex partial seizures [3, 4, 5]. However, these studies have used only a small number of NIRS channels and/or have recorded seizures that were chemically-induced. Methods: In the present study, the value of NIRS to localize the ictal onset zone was assessed in 9 patients undergoing pre-surgical assessment for refractory partial epilepsy. All patients underwent a prolonged EEG-NIRS recording using 19 EEG in-house electrodes (EEG video-monitoring; Compumedics, USA) combined with 128 NIRS channels (ISS, USA) in order to record spontaneous seizures. Results were compared to the reference standard, i.e. the epileptogenic zone as determined by a combination ictal EEG (9/9), ictal SPECT (8/9), EEG-fMRI(9/9), MEG(9/9) and intracranial EEG recordings (4/9). Results: Nine patients (age 8-47 y-o, 5 male/4 female) were studied with simultaneous EEG-NIRS. All had refractory partial epilepsy, seven of which were non-lesional. Based on multimodal analysis of semiological, anatomical, functional and electrophysiological data, four had frontal lobe epilepsy, one had frontoparietal lobe epilepsy, two had temporal lobe epilepsy and one had occipital lobe epilepsy. During simultaneous EEG-NIRS recording, electrical and/or electro-clinical seizures were recorded in all patients. Although seizure symptomatology differed across patients, all seizures were associated with hemodynamic changes consisting in an increase of rCBV, HbT and HbO over a specific area. The latter was in good concordance with the reference standard except for one patient with seizures originating from the left anterior cingulate gyrus but producing right more than left bifrontal activation. Conclusions: This study suggests that continuous NIRS-EEG is feasible with the potential to contribute advantageously to the localization of the epileptogenic zone. Further evaluation is required to determine its place in the presurgical evaluation of refractory epileptic patients. [1] Watanabe, E. et al. Neuroscience Letters, 256, 49-52, 1998. [2] Gallagher, A. et al. Epileptic Disorders, 9, 241-255, 2007. [3] Sokol, D.K. et al. Seizure, 9, 323-327, 2000. [4] Watanabe, E. et al. Journal of Biomedical Optics, 5, 287-290, 2000. [5] Watanabe, E. et al. Epilepsia, 43, 50-55, 2002.