Abstracts

Rationale: The significance of ictal infraslow activity (ISA) in structural epilepsy is not well established. It has been increasingly a topic of interest due to availability of commercial EEG machines and no need for DC amplifiers. This study is to demonstrate visual analysis of ISA, in addition to ictal conventional EEG (focal spikes, rhythmic activity, background attenuation and low-voltage fast activity) may help to better define an epileptogenic region (ER).Methods: We retrospectively studied 20 consecutive patients with medically intractable epilepsy (MIE) caused by focal cortical dysplasia (FCD) who underwent resective epilepsy surgery after extraoperative invasive EEG monitoring and achieved seizure freedom or significant seizure improvement (Engel class 1 and 2) for at least 1 year. The ictal EEG records performed by XLTEK system were analyzed using both convetional (1-70 Hz) and ISA (0.01-0.1 Hz) bandpass filter. We limited to analyze not more than 5 seizures for each patients.Results: The ISA and ictal conventional EEG (icEEG) were noted in all patients. It was less widespread than icEEG and usually seen at the center of ER. It was usually easier to recognize than icEEG especially low-voltage fast activity (LFA). ISA is usually more prominent in temporal lobe than neocortical epilepsy. It was noted before, at or after icEEG. It can be seen at seizure onset and offset in the same electrodes in some patients. ISA was in the ER which needed to be resected in all patients who achieved either seizure freedom or significant seizure improvement.Conclusions: ISA may be one of biomarkers of epileptogenic net work. Visual analysis of ISA in addition to icEEG helps to better define an epileptogenic region which may lead to better seizure outcome in pediatric patients with MIE caused by FCD. Analysis of ISA does not require special EEG equipment and should be a gold standard of interpreting intracranial EEG recording.