Direct Current (DC) Shifts and High Frequency Oscillations in Mesial Temporal Lobe Epilepsy Patients (P04.013)

Abstract

Objective: The ictal DC shifts are expression of fast neuronal firing (HFO) in the epileptogenic zone. Background It has been reported that evaluation of ictal DC shifts could help in localizing the epileptogenic area and HFO, especially fast ripples, occur almost exclusively in the epileptogenic zone. In this study we evaluated the hypothesis that ictal DC potentials are an expression of fast neuronal firing (HFO). Design/Methods: 15 patients with medically refractory mesial temporal lobe epilepsy underwent depth intracranial monitoring. 69 ictal EEGs recorded at 1000 Hz sampling rate were studied. For each recorded seizure the EEG onset was studied with the following 3 recording settings: 1.Traditional EEG: Time constant = 0.03 seconds; Display: 15 seconds per page; High Frequency Filters: 120 Hz; Sensitivity: 100 uV. 2. HFOs: TC = 0.001 seconds; Display: 5 seconds per page; HFF: 300 Hz; Sensitivity: 15 uV. 3. Ictal DC shifts: TC = 10 seconds; Display: 300 seconds per page; HFF: 30 Hz; Sensitivity: 100 uV. Results: DC shifts occurred in 96% of the clinical seizures. DC shifts occurred before, after or at the time of traditional EEG seizure onset. Negative and positive DC shifts can be seen. HFOs occurred in 84% of the clinical seizures and mainly after traditional EEG seizure onset. The frequency of the HFOs increased in 65% of the seizures as seizure progressed. In all cases the maximum amplitude of the DC shifts and also of the HFOs occurred at the electrodes of traditionalEEG seizure onset. Conclusions: The information from both DC shifts and HFOs complements and strengthens the traditional EEG findings in confirming the location of the epileptogenic area. Traditional EEG seizure onsets, DC shifts, and HFOs do not occur simultaneously indicating that they are an expression of different neurophysiological phenomena occurring during an epileptic seizure onset. Supported by: Dr. Shasha Wu received financial support for research activities from Pfizer Medical and Academic Partnerships (MAP) Program, the former The National EpiFellows Foundation (NEF) Research Grants Program. Disclosure: Dr. Wu has received research support from Pfizer Inc, The Academic Partnerships (MAP) Program and The National EpiFellows Foundation (NEF) Research Grants Program. Dr. Luders has nothing to disclose.