Abstracts

Rationale: Genetic generalized epilepsies (GGE) constitute a rubric of several electroclinical syndromes. Although the use of electroencephalography (EEG) in the diagnosis and classification of GGE is well established, its value as a predictor of seizure freedom is less well defined with studies reporting variable and conflicting results. To our knowledge, this is the first study to evaluate quantified EEG data with seizure freedom. Methods: We performed a study of 83 patients (mean age 26.8±9.9, range 11-58 y) with GGE on treatment, diagnosed and classified according to the International League against Epilepsy criteria and subsequently validated by a panel of epileptologists. All had 24-hour ambulatory EEG recordings. All EEGs were visually analyzed and manually scored by the same investigator. A custom-made electronic database was used for data entry. Epileptiform discharges were classified as generalized paroxysms (GP) (duration ≥2 sec) and fragments (duration <2 sec). Furthermore, the morphology of each discharge (spike-wave, polyspike, polyspike-wave or combination) and the state (awake, sleep) were recorded. The total duration of epileptiform discharges over 24 hours was defined as total spike density (TSD). The average duration of epileptiform discharges over an hour during wakefulness and sleep were defined as awake (ASD) and sleep spike density (SSD) respectively. The time lag from morning arousal to the first GP was also measured in each case. Clinical and demographic data including the length of seizure freedom (LSF) was collated by interviewing the patient using a validated seizure questionnaire on the day of ambulatory EEG and prospectively at six month intervals. We applied Spearman's correlation to determine the strength of association between the LSF and various EEG parameters. Results: The LSF demonstrated strong inverse correlation (correlation coefficient ρ≥0.5) with TSD, ASD and SSD in childhood absence epilepsy (CAE), and with ASD in juvenile absence epilepsy (JAE)(Table). A strong inverse correlation between the LSF and the maximum duration of GP was found in juvenile myoclonic epilepsy (JME) and CAE. The time lag from morning arousal to the first GP demonstrated a strong positive correlation with LSF in CAE and inverse correlation in JME and generalized epilepsy with generalized tonic-clonic seizures only (GTCSO). Only in CAE, the total 24-hour duration of polyspikes and polyspike-wave discharges showed a strong inverse correlation with LSF. Conclusions: For the first time, our study provides evidence that specific EEG parameters are associated with improved seizure freedom in GGE and may differ among electroclinical syndromes. In general, the burden of epileptiform discharges, in particular the 24-hour density and maximum duration of GP, is associated with reduced seizure freedom. This observation will help us understand the complex paradigm of epileptogenesis, cortical excitability and prognosis in GGE. It will also help epileptologists develop EEG markers to predict prognosis.