Abstracts

Rationale: The “spike onset zone (SpOZ)” is a newly developed concept which was derived from the study of functional magnetic resonance imaging (fMRI). SpOZ indicates the area where interictal spikes originate. Although fMRI has a good spatial resolution, the time resolution does not accommodate to the temporal dynamics of interictal spikes. Magnetoencephalography (MEG) had spatiotemporal resolution, but conventional dipole analysis is difficult to detect the SpOZ because of its low signal to noise ratio at spike onset. Gradient magnetic-field topography (GMFT), one of the spatial filters, is suitable to analyze the spatiotemporal dynamics of epileptic spikes. We hypothesized that the SpOZ can reflect the primary epileptogenic zone rather than the zone that was analyzed at the spike peak, which could be called the spike peak zone (Sp-PZ). In addition, the extent of Sp-OZ and its correlations with Sp-PZ reflect the differences in the underlying entire epileptogenic zone and network. The present study aimed to evaluate the significance of the Sp-OZ for planning the surgical strategy for drug-resistant focal epilepsy. Methods: This study involved the patients with neocortical epilepsy due to focal cortical dysplasia (FCD) in 41 (type I, 17; type IIa, 13; type IIb, 11), tumor in 6, and tuberous sclerosis (TS) in 7. Preoperative MEGs were analyzed using GMFT for SpOZ and equivalent current dipole analysis for SpPZ. The distributions of the SpOZ and its correlation with Sp-PZ were retrospectively compared among each lesion group. Results: The mean distributions (±standard deviation) of SpOZ were significantly larger (P=0.004) in TS (4.2±3.0, range 2–10) than other pathology (FCD type I, 2.2±0.3, range 1–4; type IIa, 2.7±0.4, range 1–5; type IIb, 1.8±0.4, range 1–3; tumor, 2.0±0.5, range, 1–3). FCD type IIb were likely to show complete concordance between SpOZ and SpPZ (7/11, 63.3%), while FCD type IIa (9/13, 69.2%) and tumor (5/6, 83.3%) showed more partially concordance. FCD type I (6/17, 35.3%) and TS (2/7, 28.6%) had more discordance between SpOZ and SpPZ (P=0.013). Conclusions: The distributions of SpOZ and its correlation with SpPZ were related to the epileptogenic pathology. FCD type IIb and tumor are considered to have a restricted epileptogenic zone, whereas FCD type I, IIa and TS to have an extensive epileptogenic zone and a complex epileptic network. There was a definite difference in the epileptogenic zone among epileptogenic lesions; hence, an individual surgical strategy taking into account the correlation between Sp-OZ and Sp-PZ could be considered. Funding: No funding