Abstracts

Epileptologists have observed that considerable differences exist between the time of first ictal EEG activity and the initial clinical manifestations of a seizure. Recording from intracranial electrodes currently offers us the earliest view of this ictal electrical activity. The window of time between ictal EEG and clinical onset is of interest because, if long enough, it might be used to accomplish some intervention, thereby aborting a seizure or diminishing the harm accompanying unavoidable seizures. A retrospective review was performed on all patients with focal epilepsy who underwent intracranial video-EEG monitoring (ICEEG) at the Cleveland Clinic Foundation between January 2003 and January 2005. For each patient demographic data was collected and the ICEEG seizure recordings were reviewed. To calculate the time difference from ictal EEG onset to clinical seizure onset, only those seizures with both clear focal EEG onsets as well as a clear clinical onsets were used. Clinical onsets were defined as one of the following: 1) patient self-report of an aura or pressing seizure button, 2)clear change in facial expression, 3) change in responsiveness as determined by interaction with others, 4)onset of automatisms 5)onset of motor seizure. In the group of patients who had [gt]1 seizure that was analyzed, we then calculated the percentage of patients in that group who had a minimum time from EEG to clinical seizure onset of [ge] 10s in at least 80% of their seizures. 31 patients who had a total of 268 seizures were studied. The mean age was 26.6, range [7-48]. The mean number of seizures recorded/patient was 8.65 (SD8.68), range [1-50]. The mean number of seizures/patient with both clear focal EEG onset and clear clinical onset was 3.32 (SD 2.81), range [0-9]. The mean time from ictal EEG onset to clinical seizure onset was 35.13s (SD 87.90), range [-2.14 to 432.42]. The subgroup of patients who had [gt]1 seizure with both clear focal EEG onset and clear clinical onset consisted of 20 patients. In this group, 40% (n=8) had a time from EEG to clinical seizure onset of [ge]10s in at least 80% of their analyzed seizures. These patients represent 27% of the total study population. Our study shows that in about 27% of patients with focal epilepsy who undergo ICEEG there is a considerable time difference ([gt]10s) between ictal ICEEG onset and clincal onset in at least 80% of their seizures. This information is useful in that it supports the rationale for creating EEG based interventions that may warn of, or prevent clinical seizure onset.