International League Against Epilepsy Updates Epilepsy Classification System

Proper classification of seizures can help aid in the diagnosis, treatment, and prognosis of seizure disorders.
Proper classification of seizures can help aid in the diagnosis, treatment, and prognosis of seizure disorders.

Since the International League Against Epilepsy (ILAE) published the last Classification of the Epilepsies in 1989 as a ratified version of the original 1985 document, there have been significant scientific and clinical advances in epilepsy research and management.1 A new version by ILAE's Commission for Classification and Terminology aims to account for these developments with a more comprehensive system.2 The update was published in Epilepsia in March.

In addition to its utility in guiding clinical care, the classification helps to inform epilepsy research and the development of new treatments for the disorder. It provides “a framework for understanding the type of seizures that the patient has, the other seizure types that are more likely to occur in that individual, the potential triggers for their seizures, and often their prognosis,” and it indicates the risk of certain comorbidities, the investigators wrote.2

The updated classification process includes 3 levels, starting with diagnosis of the seizure type, which is outlined in another revised ILAE position paper on the new operational classification of seizure types.3 “The purpose of such a revision is to recognize that some seizure types can have either a focal or generalized onset, to allow classification when the onset is unobserved, to include some missing seizure types, and to adopt more transparent names,” as explained in the paper.3

Classifying Seizure Type

A companion article serves as an instruction manual on how to use the new seizure classification system.4 The investigators noted that the classification is operational because there is insufficient knowledge to allow for the development of a scientifically-based classification, and they add that it “does not represent a fundamental change, but allows greater flexibility and transparency in naming seizure types.”

The first step in seizure classification is to identify onset as focal, generalized, or unknown. Focal seizures may then be further specified by the patient's level of awareness during the seizure, if known. For example, a “focal aware seizure” replaces the previously used term “simple partial seizure,” and a “complex partial seizure” would now be termed a “focal impaired awareness seizure,” which denotes impaired awareness at any point in the seizure.

Next, focal seizures may be characterized as having motor or nonmotor onset, and generalized seizures should be identified as motor or nonmotor (absence) seizures. Depending on the level of detail desired, the clinician can use either the basic seizure classification chart or the expanded chart, which includes specific motor and nonmotor symptoms and types under the different seizure categories. Additional descriptors are encouraged when available.

To further characterize seizures of unknown onset, the classification now offers several features that can be noted, including motor or nonmotor, tonic-clonic, epileptic spasms, and behavior arrest. A seizure initially marked as having unknown onset may eventually be reclassified as having focal or generalized onset, although any associated features previously noted would still be relevant.

Classifying Epilepsy Type and Syndrome

It may not be possible for the clinician to progress past the classification of seizure type, either due to limited testing resources or insufficient information. Otherwise, the next step is to diagnose the epilepsy type based on clinical grounds and supported by electroencephalogram (EEG) results. The types include focal, generalized, or — new to the 2017 classification — combined generalized and focal. This type was added to capture patients with both types of seizures, such as those with Dravet syndrome and Lennox-Gastaut syndrome.

Epilepsy type can also be classified as “unknown” when it is known that a patient has epilepsy but there is inadequate information or testing to distinguish the type as focal or generalized. Unknown epilepsy type is not always concordant with unknown seizure type.

The third step in classification — when possible — is diagnosis of the epilepsy syndrome, which “refers to a cluster of features incorporating seizure types, EEG, and imaging features that tend to occur together,” the investigators wrote.2 “It often has age-dependent features such as age at onset and remission (where applicable), seizure triggers, diurnal variation, and sometimes prognosis.”

Certain syndromes may be linked with distinct comorbidities and imaging findings, as well as specific implications regarding etiology and treatment. These include the idiopathic generalized epilepsies, which the clinician has the option of labeling “genetic generalized epilepsy” when appropriate.

Etiology, Comorbidities and New Terms

It is advised that clinicians start trying to determine etiology as soon as patients present with their first epileptic seizure. In accordance, the revised classification includes 6 etiologic groups with potential treatment implications: structural (genetic or acquired or both), genetic, infectious, metabolic, immune, and unknown. More than one category can apply to a patient, and the clinical importance of each may vary depending on the patient and situation. 

The researchers emphasize the need to consider the wide range of potential comorbidities that a patient with epilepsy may have. They also introduce new terms such as “developmental and epileptic encephalopathy;” the word “benign” as a descriptor has been replaced with “self-limited” to indicate the likelihood of spontaneous resolution, and “pharmacoresponsive” to reflect the likelihood that the syndrome can be controlled with antiepileptic therapies.

“The desired outcome for the ILAE 2017 classification is greater ease of communication about seizure types among clinicians, the nonmedical community, and researchers,” the investigators stated.4 “Future empirical classifications will be developed until knowledge is sufficient to construct a classification based on the fundamental reasons that there are different seizure types.”

References

  1. Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia. 1989; 30(4):389-399.
  2. Scheffer IE, Berkovic S, Capovilla G, et al. ILAE classification of the epilepsies: position paper of the ILAE Commission for Classification and Terminology [published March 8, 2017]. Epilepsia. doi:10.1111/epi.13709
  3. Fisher RS, Cross H, French JA, et al. Operational classification of seizure types by the International League Against Epilepsy: Position Paper of the ILAE Commission for Classification and Terminology [published March 8, 2017]. Epilepsia. doi:10.1111/epi.13670
  4. Fisher RS, Cross H, D'Souza C, et al. Instruction manual for the ILAE 2017 operational classification of seizure types [published March 8, 2017]. Epilepsia. doi:10.1111/epi.13671
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