Abstracts

RATIONALE: New technology and methods were used to perform long term, scalp recordings to localize direct current (DC) EEG shifts during spontaneous temporal lobe seizures. The objective of the study was to define how consistently scalp-detected ictal DC-shifts lateralize to the side of onset in focal epilepsy as defined by routinely used, noninvasive and invasive methods.
METHODS: DC-EEG recordings were performed on seven patients with temporal lobe seizures for periods from 1.5 to 24 hours, capturing 35 seizures in seven patients at bedside. All recordings were performed simultaneously with conventional video-EEG (from scalp in five, and intracranial in two patients). Seizures in four of these patients were demonstrated by subdural electrodes to arise in the mesial temporal lobe. Ictal DC-shifts were evaluated by comparing them to the temporal evolution of ictal discharges, and by comparing the lateralizing information of DC-shifts to all the other clinical information used for presurgical evaluation. The side of origin of each patient[ssquote]s seizures was determined by consensus at epilepsy conference on the basis of the conventional EEG, neuroimaging, and the other presurgical diagnostic tests, with participants blinded to the DC-EEG results. Six of the seven patients went on to neurosurgical treatment.
RESULTS: We observed DC-shifts of considerable amplitude (30-150 [mu]V relative to vertex) beginning within few seconds after every seizure. Ictal DC-shifts lasted for the whole seizure, or until the recording was obscured by movement artifacts. In seizures with mesial temporal lobe onset (n=7) the polarity of the DC-shift was initially positive, changing to negative after spread of the seizure to lateral temporal regions. In every case, the side of the initial DC-shift was the same as the lateralization of the seizures determined at epilepsy conference.
CONCLUSIONS: To our knowledge this is the first study in which non-invasive, scalp recorded DC-EEG techniques have been used to record focal seizures in humans. We demonstrate that by using appropriate recording techniques DC-shifts are consistently observed. The lateralization of these DC-shifts agree with that obtained from conventional EEG and other parts of the presurgical evaluation. The slow shifts seen during mesial temporal lobe seizures indicate that scalp-recorded DC-EEG might be particularly helpful in lateralizing seizures of hippocampal origin. This method warrants further study to determine if it might reduce the need for invasive monitoring in patients where ictal lateralization on conventional scalp monitoring is equivocal.
[Supported by: Finnish Academy, Finnish Cultural Foundation, Arvo and Lea Ylppö Foundation, and the Regional Epilepsy Center.]