Tonic and tonic-clonic seizures in the first year of life: Insights from electrographic features

Objective: We studied the electrographic features of tonic seizures (TS) with bilateral contraction and tonic-clonic seizures (TCS) without focal signs occurring during the first year of life to evaluate if there is a correlation with outcome. Methods: We retrospectively reviewed patients aged 1 to 12 months with at least one TS or TCS recorded with video-EEG between 2011 and 2021 in our Epilepsy Monitoring Unit. We analyzed the following electrographic features: seizure duration, presence and duration of focal ictal EEG onset, and post-ictal generalized EEG suppression (PGES). Among clinical variables, we collected age at epilepsy onset, age at TS and TCS recording, response to anti-seizure medications, genetic and neuroimaging findings, epileptic syndrome classification. Results: Overall, we recorded 2577 seizures in 1769 patients. One-hundred-twenty-eight seizures (5%) were clinically labeled either as TS or TCS in 41 patients (2%). Out of 41 patients, 17 (41%) presented with TS, and 24 (59%) with TCS. Thirteen patients (32%) had a Self-limited Epilepsy, and 28 (68%) a Developmental and Epileptic Encephalopathy (DEE). Seventy-two percent of genetically tested patients had pathogenic gene variants. None had structural epilepsy. Mean age at epilepsy onset was 4.48 months (range 3 days-12 months). Age at seizure onset was earlier in patients presenting with TS versus patients presenting with TCS (2.31 months vs. 6.01 months; p = 0.001) and in DEEs versus Self-limited Epilepsies (3.23 months vs. 7.16 months; p = 0.001). TS were exclusively present in DEEs (p = 0.001), and TCS were recorded in both DEEs and Self-limited Epilepsies. Focal ictal EEG onset was evident in 92 % of TCS, and in none of TS. Generalized ictal EEG onset was documented in 100 % of TS, and in 8 % of TCS. Focal ictal EEG onset occurred more frequently (100 % vs. 32 %; p = 0.000) and was significantly longer (30.61 s vs. 16.22 s; p = 0.020) in Self-limited Epilepsies versus DEEs. PGES was observed in 18 out of 41 (44 %) and was more frequent in Self-limited Epilepsies (p = 0.026). Significance: This study provides insights into the electroclinical features of TS and TCS in infants that may help distinguish Self-limited Epilepsies from DEEs soon after epilepsy onset.