Abstracts

Patients admitted to epilepsy monitoring units (EMU) often have their antiepileptic drugs (AED) reduced or withdrawn to increase seizure frequency and facilitate analysis within the limits of the typical admission. Seizure classification and localization are typical goals of EMU admissions. There has been relatively little study of seizure dynamics, evolution, and duration. Sequential seizures from 8 patients with mesial temporal onset seizures requiring intracranial electrode arrays; and whose AEDs were discontinued during the EMU stay were analyzed. A total of 62 seizures were analyzed. The duration of partial seizures was determined by visual analysis of intracranial EEG (ICEEG) recordings of ictal activity from the electrode closest to the seizure focus. In addition, seizure duration was measured by the duration of the increase in Gabor atom density (GAD), a complexity measure derived from time-frequency decomposition of the ICEEG, previously developed and shown (Jouny et al., 2003) to correlate with seizure duration. Seizure durations measured independently by visual analysis of ICEEG and GAD were not statistically different (paired t-test, p=0.507). Seizures occurring in clusters (operationally defined as 3 or more seizures in a 4-hr period) did not significantly differ in duration and dynamical composition from non-clustered seizures. We could analyze the effects of AED withdrawal in 5 patients whose seizures were spread over more than 24 hours. For these 5 patients, the duration of partial seizures that did not secondarily generalize did not show a significant increase with AED withdrawal during the EMU stay. While the numbers of patients analyzed do not allow conclusions regarding specific AED effects, the results of this study do not indicate that AED withdrawal affects the duration of partial seizures. The results here provide further confirmation of the utility of the GAD method as a quantitative measure of seizure duration. In addition these preliminary results suggest that AED therapy, while reducing seizure number and secondary generalization, may not significantly alter the intrinsic dynamics of individual partial seizures. (Supported by NIH grant NS 33732)