The new ILAE classification

Abstract

The International League Against Epilepsy (ILAE) classification of seizures (Commission on Classification and Terminology, 1981) and of epilepsy syndromes (Commission on Classification and Terminology, 1989) represented a major step forward and improved our ability to speak a common language when dealing with epilepsy. In conjunction with the Guidelines for Epidemiologic Research (Commission on Epidemiology and Prognosis, 1993), they provided a framework for the explosion in research on epilepsy around the world. Because the classification scheme is several decades old, the ILAE decided to update it (Commission on Classification and Terminology, 2010), an effort of several years and considerable work. In this era of constant change in our knowledge and understanding of medicine, it is important to periodically check that old assumptions remain valid. There are two approaches to this process. The first approach is to update the old without discarding it. This is the approach taken by the World Health Organization (WHO) in updating the International Classification of Diseases, 9th Revision (ICD-9) to create the ICD-10. Some diagnoses are changed and updated, but the overall conceptual framework remains intact. The second approach is a more radical restructuring, which is sometimes needed. The disadvantage is that prior work may not be interpretable in the new framework. The ILAE Commission combined both approaches with somewhat mixed results. The new classification of seizures is a good example of where the changes reflect our current knowledge and the old system is updated but not discarded. The reintroduction of infantile spasms as a seizure type, the simplification of absence seizures, and the addition of some specific seizure types are all improvements that were needed. The change in partial seizures (now called focal seizures) is an improvement that still recognizes the importance of preserving consistency with the old classification. Although the terms simple and complex partial have been discarded, the preservation of “without impairment of consciousness” and “with impairment of consciousness” as key concepts allow the use of available data to classify according to the new system. This is important as I suspect it will be many years before the nonspecialist switches to the new system, so it is critical that we are able to classify seizures where the available information is still based on the old system in accordance with the new one. The Commission has taken great pains to ensure that this is possible and this greatly enhances the value of the new system. The new classification of syndromes is somewhat more problematic but still represents incremental change. In terms of individual syndromes, such as childhood absence epilepsy, juvenile myoclonic epilepsy, and temporal lobe epilepsy, the Commission has chosen to largely preserve them with a few changes that were reasonable and reflect current knowledge. It is not clear to this commentator why eponyms (e.g., Dravet syndrome [instead of severe myoclonic epilepsy of infancy], Panayiotopoulos syndrome) have replaced more descriptive terms. Overall the definitions of the individual syndromes also reflect a welcome incremental change. The most problematic part of the new classification is the change in the classification of etiology. The new classification has chosen to rely on “genetic” as a major category. There are two major problems with this approach. The first is that although rare single gene epilepsy syndromes such as SCN1A have contributed significantly to our understanding of the pathophysiology of epilepsy, they are rare and most likely account for only a few percent of cases. It seems strange to base a major part of the etiology classification on rare cases. In many situations, including focal epilepsy syndromes, there is most likely an interaction between genetic susceptibility and environmental causes. Even in classic “genetic” epilepsies such as childhood absence, it is now clear that a variety of different mutations will result in the same phenotype and that in many cases we may not identify a specific genetic defect. The reliance on genetics to solve the puzzle is more a hope for the future than a reflection of current reality. Only time will tell whether that hope was justified. Finally, a major reason to lump together a group of syndromes is that they share many phenotypic features. The old classification definition of “idiopathic” was admittedly ambiguous. But one of the implications, whether explicitly stated or not, was that these were age-dependent epilepsies that responded well to medications in otherwise neurologically intact children. In that sense benign rolandic epilepsy, childhood absence epilepsy, and juvenile myoclonic epilepsy were all similar, although remission rates were clearly different. The “idiopathic generalized epilepsies” also shared the electroencephalography (EEG) phenotype of either 3 Hz spike-and-wave or rapid (> 3Hz) spike-and-wave. Having discarded the term idiopathic, we need to carefully think about finding a way to still talk about these age-specific epilepsies, such as the primary generalized epilepsies, that account for a significant proportion of childhood-onset epilepsy and do not quite fit neatly in any one bin in the new classification. We also have to be concerned that, unlike the revised classification of seizures, the new classification of etiologies is a radical restructuring that does not permit mapping the old terms onto the new. Furthermore, a classification that is stated to be a “work in progress” makes it difficult to do research with a single language. When all is said and done, there was a need to update the classification. Indeed, the new seizure classification and individual syndromes more accurately reflect our current understanding of the epilepsies. It remains to be seen whether the new classification of etiology will hold up or will require revision. Fortunately, because the individual syndromes are preserved, we can still continue to have a shared conversation even though we may disagree on some aspects. It is also nearly impossible to reach consensus on all these issues. The Commission is to be congratulated on a very thoughtful update of the classification, which is a move forward. I have no disclosures relevant to this activity. I confirm that I have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.

Keywords

Affiliated Institutions

• Albert Einstein College of Medicine US

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