Epilepsy Fellow Vanderbilt University Medical Center Brentwood, Tennessee
Rationale: Idiopathic generalized epilepsy (IGE) patients commonly have generalized tonic clonic seizures (GTCS). Elucidating the networks that mediate GTCS may lead to better understanding the basic mechanisms underlying these seizures and thus facilitate the development of improved diagnostic and therapeutic options. A first step in identifying GTCS networks is to characterize the initial semiology and associated spatiotemporal electrographic characteristics. Methods: Vanderbilt epilepsy monitoring unit (EMU) reports from January 2009 - February of 2019 were retrospectively screened for the presence of GTCS. Inclusion criteria included age ≥ 18 with IGE, recorded GTCS, normal neurologic exam, and absence of focal EEG or MRI findings. We identified categories of initial semiology and electrographic changes and determined the proportion of GTCS in each category. Results: Forty-six patients met inclusion criteria with a total of 77 GTCS. The initial semiology clustered into five groups: “head turn” 17 seizures (22%), “myoclonic” 10 (13%), “behavioral arrest” 24 (32%), “tonic” 17 (22%), and “other” 8 (11%). There was no significant difference in the fraction of seizures in any initial semiology category (P >0.058).Initial EEG pattern was available in 75 seizures and clustered into four groups: 2.5-6 Hz: 41 seizures (55%), 6-12 Hz: 14 seizures (19%), >12 Hz: 12 seizures (16%), and other: 8 seizures (11%) (P< 0.001). There was no significant relationship between the initial EEG pattern and initial semiology categories.Twenty-one patients had more than one primary GTCS (2.4 ± 0.2). Patients with an initial semiology of tonic seizures had repeat tonic seizures (79±15%) significantly higher than chance (P = 0.045), but the probability of repeat head turn (33±15%) or behavioral arrest (46±14%) seizures was not greater than chance.Patients with initial EEG patterns of 2.5-6 Hz, 6-12 Hz, and > 12 Hz had the same initial EEG pattern for 73±11%, 67±21% and 92±8 % of the seizures, respectively. The percentage of repeat >12 Hz seizures was significantly more likely than the probability of all >12 Hz seizures (P = 0.011). Conclusions: The categorization of the majority of GTCS into discrete initial semiology and electrographic patterns suggests that a limited number of brain networks are activated during these seizures. However, the absence of a significant association between the initial semiology and electrographic pattern indicates neurophysiological aspects of the seizure other than onset frequency are responsible for shaping the semiology. The observation that patients often exhibit GTCS with different initial semiology and EEG onset patterns suggests that IGE patients can develop GTCS through activating different networks. However, the finding that patients with either a tonic or fast EEG onset were significantly more likely to have subsequent GTCS of the same type suggest this subset of patients may utilize a single network to form GTCS. Funding: Please list any funding that was received in support of this abstract.: n/a
