Beyond Myoclonus-Seizures, Epilepsy Syndromes and Atypical Electroencephalographic (EEG) Findings in Children With Subacute Sclerosing Panencephalitis.

BackgroundSubacute sclerosing panencephalitis is typically characterized by myoclonic jerks, cognitive decline, movement disorders, and periodic complexes on electroencephalography (EEG). Although myoclonus is a hallmark feature, other seizure types including generalized/focal seizures are less commonly described in subacute sclerosing panencephalitis. We aimed to study seizure frequency, types, spectrum of epilepsy syndromes, and atypical EEG findings among children with subacute sclerosing panencephalitis.Materials and MethodsA retrospective chart review of 100 children (aged 1-18 years) diagnosed with subacute sclerosing panencephalitis (April 2020-April 2024) was conducted. Data collected included demographics, clinical features, seizure semiology, EEG, and magnetic resonance imaging (MRI) findings. Outcome measures included the proportion of children experiencing seizures beyond myoclonus, the spectrum of seizures and epilepsy syndromes as per the International League Against Epilepsy (ILAE) 2017 seizure classification and the ILAE 2022 diagnostic framework for electroclinical syndromes, respectively, and description of other atypical EEG patterns.ResultsAmong 100 children (73% males, age range 5.5-10 years), 54% had seizures beyond myoclonus, which included bilateral tonic-clonic seizures in 48 children, focal seizures in 5 children, and 1 child with epileptic spasms. Six children had classifiable epilepsy syndromes, including 5 children with epileptic encephalopathy with spike-wave activation in sleep and 1 child with infantile epileptic spasms syndrome. Atypical EEG patterns, seen in 22%, included epileptic encephalopathy with spike-wave activation in sleep-like pattern, modified hypsarrhythmia-like pattern, electrodecrement within periodic complexes, etc, which correlated with advanced stages of subacute sclerosing panencephalitis.ConclusionsSubacute sclerosing panencephalitis can often mimic epileptic encephalopathies. Atypical seizure semiologies and varied EEG patterns highlight the need for strong clinical suspicion to avoid misdiagnosis and delayed disease recognition, especially in endemic countries like India.