Differences in semiology and EEG of acute symptomatic seizures after traumatic brain injuries with an EEG-based prognosis assessment of early functional outcomes

INTRODUCTION: The semiology of acute symptomatic seizures (ASz) following traumatic brain injury (TBI) varies over time and may impact the hospital course. EEGs can help to predict ASz and early functional outcomes, but the optimal timing and predictive value remain uncertain. METHODS: We retrospectively analyzed patients with acute TBI treated between 2018 and 2021 with at least one EEG. ASz were categorized as immediate (≤24 h) or early (>24 h-7d) and classified by semiology. Interictal EEG features (encephalopathy grade, epileptiform discharges [ED], and reactivity) were assessed to predict the modified Rankin Scale (mRS) at discharge. RESULTS: Of 98 patients, 35 (35.7 %) developed ASz: 22.8 % immediate, 71.4 % early, and 5.7 % both. Immediate ASz typically presented as bilateral tonic-clonic seizures (80.0 %, p = 0.018), while early ASz often manifested as non-convulsive status epilepticus (55.6 %, p = 0.018). EDs independently predicted early ASz (OR 6.4 [1.6-25.5], (p = 0.008)) but not immediate ASz. ASz were not independently associated with mRS at discharge. Severe encephalopathy and absent EEG reactivity predicted poor mRS at discharge but were mediated by narcotic use, where only absent reactivity remained significant in a subgroup without use of narcotics (OR 10.4 [1.6-68.3], (p = 0.03). The association was highest for EEGs performed >96 h post-admission and within 7 days before discharge of the last EEG. CONCLUSION: ASz semiology varies with timing, but ASz themselves did not independently predict discharge outcomes. Instead, interictal EEG features, especially severity of encephalopathy and absent reactivity, were predictors of worse mRS at discharge, mediated by concomitant narcotic use and time of examination.