Classifi cation of epileptic seizures and epilepsy syndromes

The efforts of ILAE for providing a standardized classifi cation and terminology of epileptic seizures and epilepsy syndrome; the international classifi cation of epileptic seizures in 1981 and international classifi cation of epilepsy syndromes and epilepsies in 1989, have provided outstanding achievement in promoting epilepsy care, research, and education over the past decades. However, further attempts of ILAE to improve and update the classifi cation systems have not been successful due to signifi cant heterogeneities and still incomplete knowledge on the fundamental pathophysiology of epilepsies. Despite these shortcomings, the Commission on Classifi cation and Terminology of ILAE recently published a new proposal, “Revised Terminology and Concepts for Organization of Epileptic seizures and Epilepsies”, which has generated lively discussions and debates throughout the international epilepsy communities. The basic concepts for the change seem to be rational and well taken but the proposal was not a classifi cation, which made the epilepsy communities somewhat confused and disappointed. A new proposal of classifi cation is urgently needed to replace the overdue ILAE-classifi cation. Neurology Asia 2013; 18 (Supplement 1) : 1 – 4 Address correspondence to: Dr Byung-In Lee, Department of Neurology, Yonsei University College of Medicine, Seoul, Korea. E-mail: INTRODUCTION Classification is the universal vocabulary for communication and exchange of ideas, which is essential for clinical, educational, and research achievements. The classifi cation systems in medicine may have different ranks in hierarchies with a classification system based on pathomechanisms being considered the most reliable and ranked at the highest in hierarchy, while classifi cations based on etiology, biomarkers, clusters of symptoms and signs, and characteristic symptoms are in descending orders. In epileptology, pathomechanisms of epileptogenesis or ictogenesis are still incompletely understood. Etiologies are unknown in a major proportion of patients while they are quite heterogeneous in patients with known causes of epilepsy. We still do not have any reliable biomarkers for individual cases to be useful for the formulation of classifi cation. Therefore, the current classifi cation systems of epilepsy are based on the electroclinical correlations of individual cases, which are defi ned as epilepsy syndromes (clusters of signs and symptoms occurring together) and epileptic seizures (the most characteristic symptom), which are at the bottom in hierarchy. By the leadership of International League Against Epilepsy (ILAE), the international classifi cation of epileptic seizures (ICES) was proposed in 1970 and revised in 19811, which has classifi ed seizures into two broad categories, partial and generalized seizures, on the basis of electroclinical correlations. Partial seizures were defi ned as seizures in which the clinical and EEG changes indicate initial activation of a system of neurons limited to a part of one cerebral hemisphere. They were further divided into simple and complex partial seizures based on the assessment of impairment of consciousness, with or without secondary generalization. Generalized seizures were defi ned as seizures in which the clinical and EEG changes indicate initial involvement of both hemispheres. They were further divided into generalized tonicclonic, absence, myoclonic, clonic, tonic, and atonic seizures. The ICES is simple and clinically useful for the selection of antiepileptic drugs (AEDs), thus widely accepted by international medical communities. However, there have been continuing controversies on the scientifi c basis for the dichotomies of “partial and generalized seizures”, and for the use of “impairment of consciousness” as a critical measure of classifi cation. Neurology Asia 2013; 18 (Supplement 1) 2 Continuing efforts of ILAE to improve the classifi cation to be more clinically useful have resulted in the proposal of the international classifi cation of epilepsy syndromes and epilepsies (ICE) in 1985, which was revised in 1989.2 Epilepsy syndrome was defi ned as a distinctive, recognizable clinical disorder by a complex of clinical features, signs and symptoms occurring together. The classification scheme consists of three steps; (i) First, to defi ne seizure types into localization-related (focal or partial) and generalized seizures; (ii) Second, to determine the etiology as one of three categories; idiopathic (there is no underlying cause other than a possible hereditary predisposition), symptomatic (the result of one or more identifi able disorders of the brain), and cryptogenic (presumed to be symptomatic, but the etiology is unknown); and (iii) Third, to categorize into one of known or recognized electroclinical syndromes. Syndromic diagnosis usually provides much more comprehensive information relevant to the etiology, natural courses and prognosis, and therapeutic effi cacies. Thus recognizing the patient’s epilepsy syndrome has become a firm recommendation in all guidelines of epilepsy management. In clinical practices, many physicians have found that with available clinical information, ICE is a well organized and a very inclusive system, thus most of patients can be assigned into a predetermined diagnostic category. However, there have been growing criticisms against the framework of ICE over past decades. The reasons include: (i) Only a minority of patients can be assigned into specifi c electroclinical syndromes while many patients are assigned into non-specifi c diagnostic categories, which may give a false impression of diagnostic precision; (ii) Anatomical localization of lobar epilepsies are not often accurate; (iii) It is essential to incorporate recent advances in epileptology; e.g., neuroimaging data, genetic and molecular information, and newly recognized epilepsy syndromes. In addition, there have been continuing arguments about the dichotomy of “partial and generalized”, and controversies to the terminologies of “idiopathic, symptomatic, and cryptogenic”.3 The Commission of Classification and Terminology of ILAE continues to work towards updating the classification systems. Their efforts were published in 2001 and 2006, which recognized a long list of new electroclinical syndromes, and tried to adopt evidencebased approaches. However, the Commission acknowledged that their proposal is not a new classifi cation system but only complimentary to the ICE of 1989. On the assumption of a general consensus refl ecting that the ICE of 1989 is outdated and a new classifi cation system is in urgent need for clinical application of recent advances in epileptology, the ILAE Classifi cation Commission (2005-2009) published their work, titled as “Revised terminology and concepts for organization of seizures and epilepsies”, in Epilepsia in 20104, which has raised lively discussions and further proposals. THE NEW ILAE PROPOSAL ON CLASSIFICATION AND COMMENTARIES Classifi cation of epileptic seizures The new proposal for the classifi cation of seizures is largely unchanged from the framework of ICES of 1981. However, a network concept for the defi nition of partial and generalized seizures is adopted, in which partial seizures are conceptualized as seizures originating within networks limited to one hemisphere while generalized seizure as originating at some point within, and rapidly engaging, bilaterally distributed networks. Other specifi c changes include: (i) Neonatal seizures are no longer regarded as a separate entity; (ii) Subclassifi cation of absence seizures is altered to include myoclonic absence and absence with eyelid myoclonia; (iii) Subclassifi cation of myoclonic seizures includes myoclonic tonic and myoclonic atonic seizures; (iv) Epileptic spasm is included as a separate entitiy; and (v) For focal seizures, the distinction between the different types is eliminated. However, if necessary, it is recommended to use “descriptors of focal seizures according to degree of impairment during seizures”, which are essentially identical to the previous concept of simple and complex partial seizures. Commentaries about the new proposal by the epilepsy care professional community were mainly focused at (1) the network concept about the partial and generalized epilepsies and (2) elimination of subtypes of focal seizures. The traditional concept of partial and generalized seizures was based on the distribution of abnormally hyperexcitable brain regions (or epileptogenic zone), focal vs. diffuse, which may still be correct and easier to explain the clinical features of seizures. Although recent advances in fMRI and electrophysiology have raised interests for the network concept in ictogenesis and ictal spreading, the precise identifi cation of network characteristics of partial