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

Objective: To provide a quantitative evaluation of typical electroencephalographic (EEG) abnormalities in genetic generalized epilepsy (GGE). Methods: We 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. Results: A 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%). Conclusion: Our 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. Significance: Epileptiform 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. Crown Copyright (C) 2015 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology. All rights reserved.