Abstracts

Rationale: The Generalized Tonic-Clonic Convulsion (GTCC) has been described as a stereotyped seizure consisting of a symmetric tonic posture, followed by vibratory and clonic phases - defined as movements at a frequency of >5 Hz and <5 Hz respectively. We examined how frequently the classic GTCC occurs in a population and what factors, if any, contributed to deviations from this pattern. Methods: We reviewed the video EEG of 100 consecutive inpatients of the NYU Comprehensive Epilepsy Center that had bilateral limb movements 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 in that order was categorized as "typical GTCC" (tGTCC), if one phase was absent, asymmetric or in the wrong order of progression it was considered "atypical GTCC" (aGTCC), if two phases were absent it was not a GTCC (nGTCC). All aGTCC were reviewed by at least 3 reviewers. Results: 104 seizures (41 from women) from 100 patients were reviewed, 2 patients were excluded due to obscured video. 45 had a tGTCC while 15 were aGTCC, and 42 were nGTCC - either being a tonic, myoclonic-tonic, or partial seizure with dystonic, clonic, or complex motor features. 40% of nGTCCs were reported as a GTCC by physicians/nurses and 96% of tGTCCs and 93% of aGTCCs were reported as a GTCC. The median duration (seconds) of seizures was 110.5 for tGTCC, 109.5 for aGTCC, and 95.5 for nGTCC (Kruskal-Wallis p=0.061). Table 1 shows epilepsy classifications for each of the three groups; 89% of idiopathic generalized epilepsy was associated with tGTCC and none with aGTCC. Excluding patients with no imaging data, 15/34 (44%) of tGTCC, 6/10 (60%) of aGTCC had lesional MRIs including post-operative changes (Fisher's Exact p=0.48). Conclusions: These data demonstrate that the GTCC does not always present with the classic progression from tonic to vibratory and then clonic activity; in 15% of patients overall, atypical features were observed. Of all GTCCs recorded in patients with focal seizures 28% were atypical. No patients with IGE had aGTCCs. These data demonstrate a trend for shorter seizure durations for nGTCCs versus a/tGTCC. Furthermore, tGTCCs are more frequently associated with non-lesional structural imaging. GTCCs are associated with an increased risk of SUDEP, a worse surgical outcome, and a higher risk for seizure-related injury. The association between aGTCC and these findings is unclear and requires further investigation.