Abstracts

Rationale: Detection of interictal epileptic discharges (spikes) in scalp EEG has not enough sensitivity, even in patients with pharmaco-resistant epilepsy. Currently there is a lack of reliable biomarkers of active epileptogenicity in the individual patient. “Epileptic” voltage topographic map can be found in scalp high-density EEG, even in absence of spikes (Grouiller F, et al. Brain 2011; 134:2867-2886). Aim: to assess if the clinical (31-channles) EEGs of epileptic patients without any detectable spikes contain the voltage epileptic map, specific of the individual patient.Methods: Fifteen patients (9 females, age at evaluation 30.7 years ± 4.0) with pharmaco-resistant focal epilepsy (length of disease: 19 years ± 3.51) were included. Six minutes of EEG with spikes and six minutes without any detectable spikes were selected from long-term monitoring recording during resting state (EEG 31-channels, ref: FCz). Resting-state EEG from 48 healthy control subjects (24 females, age at evaluation 32.9 years ± 9.08) were also recorded and corrected for artifacts. For the EEG of each patient, we calculated the averaged spike and its voltage map. We fitted the spike map on i) EEG of patient with visible spikes ii) EEG of the same patient without any visible spike and iii) EEGs of the 48 controls. The amount of presence of the voltage epileptic map was characterized using two criteria: mean correlation and Global Explained Variance (GEV). For these criteria statistical differences between 1) controls and EEG with spikes, and 2) controls and EEG without spikes were evaluated using z-scores.Results: The patient-specific epileptic voltage map was significantly more represented in the spike-free EEGs of patients than in EEGs of healthy controls (GEV p=0.029; mean correlation p=0.032). This difference was more accentuated for the patient EEGs containing spikes (GEV p=0.001, mean correlation p<0.001).Conclusions: Scalp EEGs of patients with pharmaco-resistant epilepsy contains the epileptic voltage map (index of epileptic activity), even in absence of any detectable interictal epileptic discharges. This finding suggests that epileptic voltage map could be a new epileptic bio-marker (SPUM grants 140332 and 141165).