Abstracts

The electro-clinical features of typical absence seizures have been reported to differ according to the epilepsy syndrome in which they occur. Systematic studies of absence seizures in newly presenting untreated patients with IGE have not been performed, nor have confounding factors affecting the semiology been scrutinised. 70 consecutive untreated children (aged 2-16 years) with newly presenting absence seizures were studied using video-EEG. Detailed electro-clinical analysis of the semiology and the ictal EEG was performed. A statistical model was used to correct for the confounding effects of state (awake, drowsing, sleep), provocation (hyperventilation, intermittent photic stimulation), epilepsy syndrome, age and seizure duration. 509 seizures were analysed in 70 children [Childhood absence Epilepsy (CAE) 37, CAE+photoparoxysmal response (PPR) 10, Juvenile Absence Epilepsy (JAE) 8, Juvenile Myoclonic Epilepsy (JME) 6, unclassified 9]. The epilepsy syndrome had a direct effect on the duration of the absence seizure, the number of spikes per wave and the presence of fragmentation of the discharge, but had no independent effect on the level of awareness of the child, the presence of eye opening or the presence of abnormal eyelid movement during the absence seizure. The age of the child, independent of the epilepsy syndrome, had an effect on the level of awareness, presence of eye opening and presence of fragmentation but not on the presence of abnormal eyelid movement, the duration of the seizure, or the maximal number of spikes per wave. The state or provocation the seizure occurred in as well as specific (unmeasured) features of the child, independently influenced the duration of the seizure, the level of awareness, the presence of eye opening, the presence of abnormal eyelid movements, the presence of fragmentation, and the maximal number of spikes per wave. This study demonstrates that the electro-clinical features of typical absence seizures in an individual are influenced by a complex interaction of age, epilepsy syndrome, state in which the seizure occurred, provoking factors and other unique features of that individual that are genetically and environmentally determined. This suggest that the seizure semiology and electrographic features per se are of limited value in distinguishing between the different common idiopathic absence epilepsy syndromes.