Revised terminology and concepts for organization of seizures and epilepsies: Report of the ILAE Commission on Classification and Terminology, 2005–2009

TLDR

Seizure classification traditionally distinguishes generalized and focal types, but the ILAE Commission redefines these terms and introduces new categories such as genetic, structural‑metabolic, and unknown to replace older labels, noting that not all epilepsies fit into electroclinical syndromes. The International League Against Epilepsy Commission on Classification and Terminology has revised concepts, terminology, and approaches for classifying seizures and forms of epilepsy. The Commission proposes a hierarchical organization of epilepsy forms, first by specificity into electroclinical syndromes, structural‑metabolic causes, and unknown causes, then allowing flexible subdivision by natural classes or pragmatic groupings to structure knowledge and identify new forms. The revised classification simplifies the categorization of generalized seizures.

Abstract

The International League Against Epilepsy (ILAE) Commission on Classification and Terminology has revised concepts, terminology, and approaches for classifying seizures and forms of epilepsy. Generalized and focal are redefined for seizures as occurring in and rapidly engaging bilaterally distributed networks (generalized) and within networks limited to one hemisphere and either discretely localized or more widely distributed (focal). Classification of generalized seizures is simplified. No natural classification for focal seizures exists; focal seizures should be described according to their manifestations (e.g., dyscognitive, focal motor). The concepts of generalized and focal do not apply to electroclinical syndromes. Genetic, structural-metabolic, and unknown represent modified concepts to replace idiopathic, symptomatic, and cryptogenic. Not all epilepsies are recognized as electroclinical syndromes. Organization of forms of epilepsy is first by specificity: electroclinical syndromes, nonsyndromic epilepsies with structural-metabolic causes, and epilepsies of unknown cause. Further organization within these divisions can be accomplished in a flexible manner depending on purpose. Natural classes (e.g., specific underlying cause, age at onset, associated seizure type), or pragmatic groupings (e.g., epileptic encephalopathies, self-limited electroclinical syndromes) may serve as the basis for organizing knowledge about recognized forms of epilepsy and facilitate identification of new forms.