Abstracts

Rationale: The Generalized Tonic-Clonic Convulsion (GTCC) is often associated with post-ictal electrographic slowing, and at times suppression. The mechanism of post-ictal EEG suppression is not known but may reflect involvement of bilateral subcortical networks. We examined the electrographic activity occurring after seizures with bilateral movement to determine if there are post-ictal features unique to the GTCC. Methods: We reviewed the video EEG of 100 consecutive inpatients of the NYU Comprehensive Epilepsy Center that had bilateral movement as part of their seizure semiology. Each seizure was reviewed by 2 reviewers; any records in which the patient was obscured on the video were excluded from further analysis. Any seizure with bilateral symmetric tonic, vibratory and clonic phases (defined as bilateral movement > and < 5 Hz respectively) in that order was categorized as "typical GTCC" (tGTCC). If one phase was absent, asymmetric or the progression was different, it was considered an "atypical GTCC" (aGTCC). If two phases were absent it was not a GTCC (nGTCC). All aGTCC were reviewed by at least 3 reviewers. The post-ictal EEG was categorized as: "suppression", defined as background voltage <10uV; "slowing" defined as decreased amplitude and/or frequency compared to baseline while still >10uV; or "no change from baseline." Results: 104 seizures from 100 patients were reviewed, 5 patients were excluded due to obscured video or EEG, leaving 97 seizures reviewed. 41 were tGTCC, 14 were aGTCC and 42 were nGTCC - either being a tonic, myoclonic-tonic, or dystonic complex partial seizure. Table 1 shows the post-ictal EEG findings across groups. A significant difference was seen (P<0.0001) with 68% of tGTCCs demonstrating post-ictal EEG suppression compared with 28% of aGTCCs and 11% of nGTCCs. Conclusions: Although post-ictal EEG suppression is seen in all three groups, it is markedly more frequent in patients with the "typical" progression of a GTCC. The significant differences between these clinically defined and distinguishable groups suggest that future studies to identify risk factors for SUDEP may benefit from a more detailed semiologic stratification.