Consistent topography and amplitude symmetry are more typical than morphology of epileptiform discharges in genetic generalized epilepsy

•24-h ambulatory electroencephalograms were done in a cohort of patients diagnosed with genetic generalized epilepsy.•The typical epileptiform abnormalities were evaluated quantitatively to demonstrate the spectrum of common and rare EEG characteristics in GGE.•Awareness of the most consistent EEG features (topography and amplitude symmetry) and their variations is important to avoid misdiagnosis.

ObjectiveTo provide a quantitative evaluation of typical electroencephalographic (EEG) abnormalities in genetic generalized epilepsy (GGE).MethodsWe prospectively performed 24-h ambulatory EEG recordings in a cohort of patients with GGE. The diagnosis was established according to the International League Against Epilepsy criteria. Details of all epileptiform discharges across the 24-h time scale were entered into an electronic database. We carried out descriptive statistics to provide a quantitative breakdown of typical EEG abnormalities.ResultsA total of 6923 epileptiform discharges from 105 abnormal 24-h ambulatory EEGs were analyzed. 96% of discharges were symmetric in amplitude with fronto-central maximum topographically. Only 24% of the paroxysms had typical morphology while 43% were regular. Photoparoxysmal response, eye-closure sensitivity and hyperventilation-induced generalized paroxysms were less common in around 10%, whereas occipital intermittent rhythmic delta activity was very rare (2%).ConclusionOur results indicate that generalized discharges with symmetric amplitude and fronto-central maxima are the most consistent findings in GGE, and other features are observed less frequently.SignificanceEpileptiform discharges displaying highly consistent amplitude symmetry coupled with fronto-central topography should provoke consideration of GGE. Recognition of variations from typical abnormalities is important to avoid the risk of misdiagnosis and delayed diagnosis.