Terminology and organization of seizures and epilepsies: Radical changes not justified by new evidence

Abstract

The classifications and terminology of the International League Against Epilepsy (ILAE) provide a conceptual framework for organizing and differentiating epileptic seizures and the epilepsies. This is essential for clinical practice and research—whether in basic mechanisms, epidemiology, or therapeutic trials. The report of the ILAE Commission in this issue of Epilepsia (Berg et al., 2010) and the previous two reports of the ILAE Task Force (Engel, 2001, 2006) aimed to revise the ILAE classifications (Commission on Classification and Terminology of the International League Against Epilepsy 1981, 1989) that are still "in force," having not been replaced by subsequent reports. The classifications are now in need of updating to reflect significant advances made in nearly all fields of epileptology in the last three decades. The Commission should be commended for undertaking a task of this magnitude. Of course no work of this nature will find universal agreement, as indicated by the responses received during the consultation process conducted on the ILAE's website. Argument and debate, hopefully constructive, is probably inevitable. Indeed it is important and should be encouraged, since the Report aims to guide clinical and research practice in the following decades. Some recommendations, if incorrect, may have long-lasting adverse effects (clinical and research) and will not be easily corrected by subsequent Commissions. The following are significant concerns that need to be considered. A major and legitimate goal of recent Commissions has been to base classifications on the application of methods used in biology to identify "separate species" and "natural classes" (Berg & Blackstone, 2006). However, this has largely proved elusive, since available evidence is patchy and sometimes contradictory, or at least open to different interpretations. Possibly as a consequence, concepts proposed by one Commission are abandoned or not developed by the next, and suggestions are made that create as many new problems as quickly as old ones are resolved. "Epilepsy seizure type" proposed by the ILAE Task Force (Engel, 2001) to "represent a unique diagnostic entity or natural class" is not mentioned and appears to have been abandoned in the new Report. The current Report lists epilepsy syndromes by age at onset. This works for some, less well for others, and is completely unsatisfactory for others: Progressive myoclonus epilepsies (PME) are listed as starting in adolescents/adults—but there are important PMEs in all age groups. The listing causes markedly different disorders to be cited adjacent to each other (e.g., benign familial infantile epilepsy and Dravet syndrome), but separates similar and probably closely related disorders (e.g., childhood and juvenile absence epilepsy). "Pragmatic groupings" are created for some (e.g., epileptic encephalopathies) but, others, some which are long-established and clinically very useful, are discarded (e.g., idiopathic generalized epilepsies and benign childhood focal epilepsies). "Hemiplegia-hemiconvulsion-epilepsy" was considered a specific syndrome in 2001, was abandoned in 2006, and is now reintroduced as a "constellation" "Continuing seizures" was introduced as a replacement for status epilepticus in 2001 but was then dropped. "Self-limited," initially applied to seizures to signify duration, is now proposed as a replacement for "benign" in epileptic syndromes. The need for radical changes to current terminology is not justified by new evidence. Some terms may be "imprecise, misused or misunderstood." However, clarifying their meaning rather than replacing them would be sufficient. New terms can be difficult to grasp and difficult to apply correctly and are equally vulnerable to misunderstanding and misuse as established ones. Fundamental changes should be made only when the case for doing so is compelling and widely accepted. The entirely new term "constellation" (alien to medicine) is unnecessary. Developing the concept of "epileptic disease" would be more in keeping with standard medical terminology. The Commission usefully redefined "generalized" and "focal" epileptic seizures to take into account new thinking on their pathogenesis and maintained their dichotomy. The proposal to abandon these terms when applied to electroclinical epilepsy syndromes is unnecessary and is unlikely to find acceptance. Although most common forms of epilepsy are characterized only by generalized or focal epileptic seizures, it is well recognized that not all types of epilepsy can be classified as either focal or generalized. This is because some epilepsy syndromes allow, by definition, the occurrence of both generalized and focal epileptic seizures and also because, to varying degrees, they can share similar pathophysiologic and genetic mechanisms. However, "hard cases make bad laws." The Commission contends that they ("generalized" and "focal" when applied to syndromes), "do not adequately reflect the processes" (the processes being unexplained) underlying conditions such as West and Dravet syndromes. Nevertheless, the differences between focal and generalized epilepsy syndromes are striking, with important diagnostic and therapeutic implications. Classifying together, for example, childhood absence epilepsy, juvenile absence epilepsy, and juvenile myoclonic epilepsy as idiopathic generalized epilepsies is scientifically sound and not simplistic. Another radical and striking recommendation by the Commission is, in relationship to etiology, abandoning the terms "idiopathic,""symptomatic," and "cryptogenic" and introducing the terms "genetic,""structural/metabolic," and "unknown." The huge advances in our understanding of the genetic mechanisms underlying disease, including the epilepsies, make it inevitable that genetics should play a major role in the classification. Indeed, it has become already common to classify some rare forms of epilepsy, such as the autosomal dominant focal epilepsies, principally on the basis of their genetic basis. Adding a class of genetic epilepsies to the etiologic classification is appropriate but should be restricted to those epilepsies that are a direct result of a known genetic defect(s) in which seizures are the core symptom of the disorder. Broadening the group is fraught with difficulty. Including those with a presumed genetic defect as the Commission proposes is no advance over the current term "idiopathic." The Commission does not attempt a listing of those epilepsies which it considers genetic, probably because this would provoke an avalanche of arguments as to which syndromes should and should not be included. There is no need to abandon the term idiopathic. Its meaning can be clarified to signify epilepsies that are of unknown etiology but which are likely to be, but are not necessarily, of genetic origin. A classification that included genetic epilepsies (as defined earlier), idiopathic epilepsies (with the meaning as currently used), structural epilepsies (as defined in the new proposals), metabolic epilepsies (also as defined in the new proposals), and cryptogenic/probably symptomatic (with the meaning as currently used) would better reflect our current state of knowledge, with the expectation that the genetic, structural, and metabolic categories would expand with time at the expense of the other categories. A conspicuous omission in this report is the lack of definitions and descriptions of individual epileptic seizures and electroclinical epilepsy syndromes. These are present in the Report by name only. This is an area in which significant advances have been made and, therefore, an update of their original, brief descriptions in the 1981 and 1989 classifications was reasonably expected. That the Reports of the ILAE's Commissions on Classification and Terminology always provoke heated debate is a sign of the strength and vitality of epileptology. The influence that classification and terminology has on how clinicians and scientists conceptualize and make sense of disorders, including the epilepsies, is profound. The responsibility borne by the Commissioners is, therefore, a weighty one, carrying, as it does, the potential to influence the course of the discipline for years to come. 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. I have no conflicts of interest to disclose.

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Affiliated Institutions

• Leeds General Infirmary GB

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