Is Interictal EEG Correlated with the Seizure Type in Idiopathic (Genetic) Generalized Epilepsies?

Objective We investigated the correlation between different interictal EEG abnormalities observed in patients with idiopathic (genetic) generalized epilepsies (IGEs) and their seizure types. Material & MethodsIn this cross-sectional study, all patients with the diagnosis of IGE, were recruited in the outpatient epilepsy clinic at Shiraz University of Medical Sciences, Iran, from 2008 through 2010. Demographic variables and relevant clinical and EEG variables were summarized descriptively. Statistical analyses were performed using independent samples T-test, Chi square and Fisher's Exact tests to determine potentially significant differences. ResultsThree-hundred thirty-six patients were diagnosed ashaving IGE. Interictal EEG findings in patients with generalized tonic-clonic seizure (GTCS) compared to patients without GTCS were not different. Abnormal EEG findings in patients with myoclonic seizures compared to patients without these were not different either. However, normal EEGs were more frequently observed in patients with history of myoclonic seizures (P = 0.0001). EEG findings in patients with absences compared to patients without absences were not different. ConclusionInterictal EEG cannot differentiate the seizure types and therefore different syndromes of IGEs. Polyspikes, 3-Hz generalized spike-wave (GSW) complexes and 3.5 - 6 Hz GSW complexes, alone or in combinations, could be observed in various seizure types and syndromes of IGE. The key element in making the correct diagnosis is a detailed clinical history.