Phenotype-driven response to sodium channel blockers in neonatal and infantile genetic epilepsies with tonic seizures.
PURPOSE To evaluate the effectiveness of sodium channel blockers (SCBs) in infants with early-onset genetic epilepsies presenting with seizures with a predominant tonic component, excluding KCNQ2/3-related epilepsies. METHODS We conducted a retrospective multicenter study including infants with genetically confirmed epilepsy, seizure onset before 12 months, and treatment with SCBs. Electroclinical features, genetic data, treatment response, and outcomes were analyzed. Treatment response was defined as seizure freedom, ≥50% reduction, <50% reduction, or worsening. RESULTS Thirty-six patients were included, of whom 25 (69%) had self-limited epilepsies and 11 (31%) developmental and epileptic encephalopathies (DEE). SCBs were effective in 23/25 (92%) patients with self-limited epilepsy, all achieving seizure freedom, and partially effective in the remaining two. In DEE, all patients showed partial, but meaningful response. Overall, 23/36 (64%) achieved seizure freedom and 13/36 (36%) had a ≥ 50% reduction in seizure frequency. No seizure worsening or treatment-related adverse events were observed. In contrast, other anti-seizure medications, including valproic acid and levetiracetam, showed limited efficacy and no seizure freedom. CONCLUSION SCBs are safe and highly effective in early-onset genetic epilepsies with tonic seizures, particularly in self-limited phenotypes. Recognition of tonic seizure semiology may guide early, phenotype-driven treatment decisions while awaiting genetic results.