Classification of Childhood Epileptic Seizures

Abstract

Definition: Epilepsy was conceptually defined in 2005 as a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures. This definition, usually applied as having at least two unprovoked seizures more than 24 h apart, was widely accepted but criticized as inadequate in some clinical circumstances. The International League Against Epilepsy (ILAE) recently accepted the recommendations for a revised practical definition of epilepsy for patients who do not meet the two unprovoked seizure criteria. In their recommendation, the ILAE task force defines epilepsy as a disease of the brain defined by any of the following conditions: (1) at least two unprovoked (or reflex) seizures occurring >24 h apart, (2) one unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk (at least 60%) after two unprovoked seizures over 10 years, and (3) diagnosis of an epilepsy syndrome. Epilepsy is considered to be resolved for individuals who either had an age-dependent epilepsy syndrome but are now past the applicable age or who have remained seizure-free for 10 years, with no seizure medicines for the last 5 years.

Classification: The 1989 classification of seizures and epilepsies by the ILAE was primarily for clinical use and aimed to provide a framework for diagnosis, thereby informing management and prognosis. In this classification, seizures were categorized as localization-related or generalized, and epilepsies were classified based on the etiology as idiopathic, symptomatic, or cryptogenic. With the advancement in our understanding of the epilepsies and the rapid technological advances in neuroimaging and molecular genetics, the etiologic terms have since taken on a variety of meanings with considerable confusion and contradictions. Thus, the ILAE in 2017 revised the concepts underlying the 1989 classification. Among other changes, the 2017 classification uses more transparent terminology and offers a less dogmatic approach so that epilepsies can be organized in a more flexible manner. The term “partial” is replaced with “focal.” “Simple partial” and “complex partial” are replaced with the more descriptive terms “with or without awareness”. The number of seizures classified as generalized has been reduced from previous classifications and epileptic spasms are recognized as separate seizure category.

The terminology for the underlying etiology has also been revised. The term “idiopathic” is replaced by “genetic,” “symptomatic” by “structural or metabolic,” and “cryptogenic” by “unknown.” In addition, other etiologic categories, namely “immune” and “infectious,” have been added. According to best current understanding, genetic epilepsy is the direct result of a known or presumed genetic defect in which seizures are the core symptoms of the disorder. Structural epilepsy is where there is a distinct structural lesion demonstrated to be associated with a substantially increased risk of developing epilepsy. Metabolic causes refer to a well-delineated metabolic defect with manifestations or biochemical changes throughout the body. An immune etiology can be conceptualized as where there is evidence of autoimmune-mediated CNS inflammation. An infectious etiology is inferred where there is epilepsy due to CNS infection or post-infection sequelae (and not just seizures in the setting of acute infection). Where the cause of the epilepsy is unknown, it is categorized as “etiology unknown” with the understanding that the cause has not yet been found. The number of patients categorized as “unknown” depends largely on the extent and level of evaluation available and thus differs widely across different healthcare settings.

The 2017 classification of seizure types and epilepsies by the ILAE, though a major step forward in the approach to epilepsy, remains a dynamic and evolving process which will continue to be revised as the understanding of the pathophysiology is aided by advances in areas such as genetics, neuroimaging, and neurophysiological studies.