DIFFERENCES BETWEEN PRIMARY AND MIRROR FOCI IN PATIENTS WITH MESIAL TEMPORAL LOBE EPILEPSY AND BILATERAL INTERICTAL EPILEPTIFORM DISCHARGES
Abstract number :
1.049
Submission category :
Year :
2005
Submission ID :
5101
Source :
www.aesnet.org
Presentation date :
12/3/2005 12:00:00 AM
Published date :
Dec 2, 2005, 06:00 AM
Authors :
1Rickey J. Reynolds, 2Muhammad Al-Kaylani, and 3Bassel Abou-Khalil
Patients with mesial temporal lobe epilepsy evaluated for epilepsy surgery commonly have bilateral independent interictal epileptiform discharges (IED) during prolonged EEG monitoring. This finding raises the possibility of independent epileptogenic foci. There are no established criteria to distinguish IED associated with ictal onsets from those that are not. This study is an attempt to find neurophysiological IED indicators in the pre-surgical evaluation to help distinguish a primary focus from a mirror focus which does not generate seizures. We retrospectively studied 75 patients who underwent epilepsy surgery at Vanderbilt Medical Center for mesial temporal lobe epilepsy and who demonstrated successful post-surgical outcomes defined as being seizure free for at least two years. From these 75 patients, 14 were found to have bilateral IED. Only ten patients had recordings available for review. The IED were evaluated by frequency of occurrence, amplitude, and field. A side to side comparison was made for the entire group. The IED incidence, average amplitude, maximum amplitude, average field and maximum field were compared with a two-tailed t-test for the primary epileptogenic focus and the mirror focus. The mean IED incidence was higher on the epileptogenic side (ratio was 7.2 to 3; p[lt]0.0002). In addition, the epileptogenic side demonstrated a higher mean IED amplitude (p[lt]0.05) as well as maximum IED amplitude (p[lt]0.005). The mean IED field was not significantly different for the two sides, but the maximum field was wider on the epileptogenic side (p=0.02). Even though this study had a small sample size, it demonstrated that in addition to the expected higher IED incidence on the epileptogenic side, mean and maximum IED amplitude, as well as maximum IED field were greater on the epileptogenic side. It is hopeful that this data may encourage a larger prospective study to determine more accurately the significance of these easily assessed values in the pre-surgical evaluation of patients with mesial temporal lobe epilepsy.