Abstracts

Rationale: The semiology of Generalized Tonic-Clonic (GTC) seizures has been established with clinical observations of ictal events and video EEG monitoring. Gastaut (1954) described the clinical and electroencephalographic ictal evolution of GTC seizures in four phases that progressed continuously in the following sequence: 1) tonic phase lasting 20 sec, 2) clonic phase lasting 40 sec, 3) period of relaxation lasting 60 sec, and 4) period of recuperation lasting 3 minutes. While clinical observations and video-EEG have been the mainstay for classification of seizures, there are relatively few studies that have examined the electromyographic evolution of these phases in a prospective multicenter study. Methods: A total of 11 NAEC level IV centers enrolled prospectively a total of 201 patients admitted for video-EEG for their standard clinical care and who had history of having a GTC seizure. The patients underwent video-EEG monitoring according to standard clinical protocols of each epilepsy center, but they were also monitored using the Brain Sentinel surface-EMG (sEMG) monitoring device to assess its clinical effectiveness. Video-EEG monitoring was reviewed independently by at least 3 board certified epileptologists for assignment of seizure classification (primary or secondary onset, seizure type), electroencephalographic onset, onset of non-facial motor manifestations, and the duration of the tonic and clonic phases of the GTC seizure. To reduce bias from patients with multiple GTC seizures, the median values were calculated for subjects with multiple GTC seizures. Results: Three board certified epileptologists were in 100% concordance while independently identifying a total of 35 patients that experienced a total of 56 GTC seizures. There were 9 patients with primary onset seizures who experienced 17 GTC seizures, and 26 patients with 39 secondarily GTC seizures. The tonic phase of primary GTC seizures lasted 12.8 sec, while the tonic phase of secondarily GTC seizures lasted 14.4 sec. The clonic phase of both primary and secondarily GTC seizures lasted 39.3 sec. There were no statistical differences in duration of tonic or clonic phases between patients with primary or secondarily GTC seizures, or between adults and children with GTC seizures. Over 94% of GTC seizures had a progressive evolution from tonic to clonic activity with no break into the evolution between the tonic and clonic phases. Conclusions: Most GTC seizures have a progressive evolution from tonic to clonic phases lasting about 14 and 39 sec, respectively with no break of convulsive seizure behaviors. These "classic" GTC seizures are similar to those described by Gastaut. There are occasional (~6%) of non-classic convulsive seizures with generalization and tonic and clonic phases but with breaks in motor behavior between these motor phases. The clinical significance of these convulsive seizures is not yet understood. There were no statistical differences in the duration of tonic or clonic phases between primary or secondary GTC seizures, or between pediatric and adult patients. Funding: Brain Sentinel sponsored this pivotal double-blinded multicenter prospective clinical trial.