Absence seizures during sleep: who would have thunk it?

Commentary Two of the most fundamental aspects of caring for children with epilepsy is knowledge of seizure type and frequency of seizures. The recent report by Sadleir calls for a reassessment of each. What is an absence seizure? The 1981 International League Against Epilepsy (ILAE) classification system of seizures described the features of an " absence attack " to include its " sudden onset, interruption of ongoing activities, a blank stare ... usually the patient will be unresponsive when spoken to " (1). The five types of absence seizures listed include: absence with impairment of consciousness only, absence with clonic components (eyelids and mouth specifically noted), absence with atonic components, absence with tonic components, and absence with automatisms. Embedded in this definition is the assumption of an electrical correlate to complete the electro-clinical seizure definition. In the case of absence, it is a generalized spike or polyspike-slow wave (GSW) discharge of >2.5 Hz. This raises the ongoing discussion of a semiological classification of seizures (2) versus one in which the EEG correlate is part of the definition. Without knowing the interictal or ictal EEG, it is not certain that the description above would correctly classify a seizure of generalized versus focal onset. This is reflected in the ILAE Glossary of Descriptive for Ictal Semiology in which the word " absence " is not to be found (3). Rather, the EEG neutral term " dyscognitive " is used to describe those " … events in which disturbance of cognition is the predominant or most apparent feature and ... " specific features of cogni-tion are impaired such as perception, attention, memory, and executive function. This discussion is most relevant to the child or adult at the initial evaluation for an event of impaired consciousness indicating that prior knowledge of the patient's evaluation shapes how we define and quantify ongoing events. This uncertainty is not present in the article under consideration as these children were selected on the basis of known absence or idiopathic generalized epilepsy based on the electro-clinical correlation, in addition to having sleep recorded on a routine EEG. Of note, the question of what constitutes a typical absence seizure has resulted in a lively and scholarly discussion in the recent literature, including such issues as which phase of the discharge is measured to determine frequency and age range for inclusion (4, 5). The need for further refinement of the criteria …