What’s in a Name? The Seizure Classification Update and What It All Means

Dr Fisher is the Maslah Saul Professor in the department of neurology and Professor, by courtesy, of Neurosurgery at the Stanford University Medical Center.

Recognizing that the conventional classification of seizure types was 36 years old and that there was room for improvement, the International League Against Epilepsy (ILAE) revised the classification of seizures.^1,2 In doing so, the ILAE acknowledged that some terms had become obscure to the public while other important seizure types were not included and seizures whose origin was missed could not be classified at all. When used, the 2017 classification system should help tailor treatments and improve outcomes for patients.

What’s changed?

There are several changes in the new classification system (Figure). Partial seizures are renamed as focal seizures. Simple partial seizures are now focal aware seizures, and complex partial seizures are focal impaired awareness seizures. Classification of level of awareness is optional and serves as a surrogate marker for consciousness. Secondarily generalized seizures are called focal to bilateral tonic-clonic seizures.

Several explicit focal seizure categories are created for automatisms, atonic, clonic, epileptic (infantile, if during the first year of life) spasms, hyperkinetic, myoclonic, tonic, autonomic, behavior arrest, cognitive, emotional, and sensory seizures. These are classified by the first sign or symptom, with the exception of impaired awareness, which defines a focal impaired awareness seizure if it occurs at any time during the seizure.

New generalized onset seizures include myoclonic-tonic-clonic (seen in juvenile myoclonic epilepsy), myoclonic-atonic (seen in Doose syndrome) and absence with eyelid myoclonia (seen in Jeavon syndrome). Some seizures can be temporarily classified even if the onset is unknown.

Clinical effect

The new 2017 classification does not change the process by which a clinician would determine whether a patient is having seizures or one of the many imitators of seizures, nor the search for a cause of the seizures. It will change the next step in the usual approach to a patient with possible seizures, which is the determination of the type of seizure. It will also improve patient-physician communication, as patients often use terms for their seizures very different from those used by their medical care team. The clearer terms in the new classification will hopefully bring greater concordance.

The new classification and nomenclature should also enhance treatment strategies, since choosing seizure medicines depends upon seizure type. Possibilities for surgical or neurostimulation therapy depend upon localization and seizure type. Greater clarity about seizure type could lead to more precise and individualized therapy. A more granular structure to the classification might facilitate future research.

To employ the 2017 ILAE classification, a clinician should follow some general rules. You need to decide whether seizure onset is focal or generalized, using an 80% confidence level. Classification based upon awareness is optional-a focal seizure is a focal impaired awareness seizure if awareness is impaired at any time during the seizure.

A focal seizure is classified by its first prominent sign or symptom, other than impaired awareness or transient behavior arrest. A focal behavior arrest seizure involves arrest of behavior as the main feature of the entire seizure. Focal seizures can be sub-classified by the designated motor or non-motor characteristics. Words may be omitted when the seizure type is otherwise unambiguous.

The new classification and nomenclature should enhance treatment strategies, since choosing seizure medicines depends upon seizure type.

After specifying seizure type, the clinician is encouraged to add descriptive information about other signs and symptoms, for example, “a focal sensory seizure with left arm numbness and delayed automatisms.” Generalized means generalized onset; bilateral means propagation to both hemispheres.

Absence is atypical if it has slow onset or offset, marked changes in tone or EEG spike-waves at less than 3 per second. Clonic refers to sustained rhythmical jerking and myoclonic to a regular unsustained jerking. An unknown onset tonic-clonic, behavior arrest, epileptic spasm, motor, or non-motor seizure might be reclassified if onset later becomes known.

Concluding thoughts

New terminology always generates a familiarization and transition period. The 2017 ILAE seizure classification is an operational modification of the system developed in 1981. When we understand why there are different types of seizures, we will be able to derive a definitive scientific seizure classification. Parallel to the seizure classification, but not discussed in this article, is a new classification of the epilepsies.³

References:

1. Fisher RS, Cross JH, D’Souza C, et al. Instruction manual for the ILAE 2017 operational classification of seizure types. Epilepsia. 2017;58:531-542.

2. Fisher RS, Cross JH, 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. Epilepsia. 2017;58:522-530.

3. Scheffer IE, Berkovic S, Capovilla G, et al. ILAE classification of the epilepsies: position paper of the ILAE Commission for Classification and Terminology. Epilepsia. 2017;58:512-521.