A Proposed Diagnostic Scheme for People with Epileptic Seizures and with Epilepsy: Report of the ILAE Task Force on Classification and Terminology

Abstract

The International League Against Epilepsy (ILAE) made a major contribution when it established standardized classifications and terminology for epileptic seizures and syndromes. This provided a universal vocabulary that not only facilitated communication among clinicians, but also established a taxonomic foundation for performing quantitative clinical and basic research on epilepsy. Much, however, has changed since the adoption of the currently used Classification of Epileptic Seizures in 1981 (1) and the Classification of Epilepsies and Epileptic Syndromes in 1989 (2). Consequently, the Executive Committee of the ILAE, which took office in July 1997, agreed that review and revision of the current classification system would be a priority for this Executive term. A Task Force on Classification and Terminology was appointed, which divided itself into four working groups concerned with Descriptive Terminology for Ictal Events; Seizures; Syndromes and Diseases; and Impairment. During the course of several meetings and vigorous e-mail discussions, the Task Force agreed that it would not be possible to replace the current international classifications with similar revised and updated classifications that would be universally accepted and meet all the clinical and research needs such a formal organizational system would be expected to provide. Rather, the Task Force is proposing a diagnostic scheme that makes use of standardized terminology and concepts to describe individual patients (Table 1). Within this diagnostic scheme, a variety of approaches to classification are possible, and some are presented here by way of example only. The Task Force views the development of specific classifications as a continuing work in progress. Flexible and dynamic classifications will be revised periodically based not only on rapidly emerging new information, but also on the resolution of problems that will inevitably be identified through use. At this point, the proposal does include several definitive changes in concepts and terminology (Table 2), and classifications are presented as examples of what could be devised in the future. Although each new ILAE classification has represented considerable effort on the part of acknowledged experts from many different countries, they have always met with a certain degree of resistance from the international epileptology community. This is because, in part, a rigid classification shapes the manner in which future generations of clinical and basic neuroscientists think about epilepsy and epileptic phenomena, thereby influencing (perhaps unduly) clinical practice and research. For instance, in the current Classification of Epileptic Seizures, the division of partial seizures into "simple" and "complex" inappropriately created the impression that impairment of consciousness had certain mechanistic implications related to limbic system involvement. Confusion, and at times vociferous objections, resulted in part from the fact that the 1970 International Classification of Epileptic Seizures had used the term "complex partial seizures" synonymously with "temporal lobe seizures"(3). Over the past two decades, detailed investigations of the anatomic substrates of ictal semiology, based largely on work carried out in epilepsy surgery centers, have strongly suggested that fundamental mechanisms of certain limbic seizures are different from those of neocortical seizures, and that both can be associated with impairment of consciousness or not. Consequently, the designation of partial seizures as "simple," or "complex," has in the process lost meaningful precision. Indeed, the 1981 Classification of Epileptic Seizures was purposely based purely on ictal phenomenology and associated EEG findings rather than anatomic substrates and pathophysiologic mechanisms, because insufficient information was available at the time to permit the authors to do otherwise. It is the belief of the Task Force that adequate evidence now exists to permit creation of a list of seizure types that represent diagnostic entities, as opposed to phenomenologic descriptions, based on known or presumed common anatomy and pathophysiology. Such diagnostic entities would, like syndromes, have etiologic, therapeutic, and prognostic implications, and could be used to supplement syndromic diagnoses, or stand alone when syndromic diagnoses cannot be made. The 1981 Classification of Epileptic Seizures also has been criticized because it is not purely semiologic; post hoc etiologic information and EEG data are often required to use it properly, and the dichotomy of "partial" versus "generalized" belies a need to avoid anatomic implications. The Task Force believes that a purely descriptive phenomenologic approach to defining ictal semiology has definite clinical value, and the new diagnostic scheme proposed here includes a modification of a previously proposed classification of ictal phenomenology (4), as an option that can be used in deta