Historical background

Descriptions of seizures date back to ancient Mesopotamia. In ~2500 B.C., the Sumerians provided the first writings about seizures.^[3]: 458 Later, in ~1050 B.C., Babylonian scholars developed the first seizure classification, inscribing their medical knowledge in the stone tablets called Sakikku or in English "All Diseases."^[3]: 458 This early classification identified febrile seizures, absence seizures, generalized tonic-clonic seizures, focal seizures, impaired awareness seizures, and status epilepticus.^[3]: 458 Samuel-Auguste Tissot (1728–1797) authored Traité de l’Epilepsie, a book describing grand état (generalized tonic-clonic seizures) and petit état (absence seizures).^[3]: 460 Jean-Étienne Dominique Esquirol (1772–1840) later introduced grand mal (generalized tonic-clonic seizures) and petit mal to describe these seizures.^[3]: 460 In 1937, Gibbs and Lennox introduced psychomotor seizures, seizures with "mental, emotional, motor, and autonomic phenomena."^[4] Henri Gastaut led the effort to develop the ILAE 1969 classification of seizures based on clinical seizure type, electroencephalogram (EEG), anatomical substrate, etiology, and age of onset.^[5]: 491 The ILAE 1981 classification of seizure included information from EEG-video seizure recordings, but excluded anatomical substrate, etiology, and age factors, as these factors were "historical or speculative" rather than directly observed.^[5]: 491 In 2017, the ILAE introduced an operational classification of seizure types.^[6] categorized based on three features: onset (focal, generalized, or unknown), awareness (for focal seizures: aware vs. impaired awareness), and predominant symptoms at onset (motor vs. non-motor). Seizure types were named using this structure, for example, a focal impaired awareness motor seizure with automatisms. Generalized seizures were divided into motor (e.g., tonic-clonic, myoclonic, atonic) and non-motor types (various absence seizures).^[6]

ILAE 2025 revision

In 2025, the ILAE released a revised seizure classification that built on the 2017 operational framework.^[2] The update introduced a taxonomic structure that distinguishes between classifiers, which define seizure types, and descriptors, which provide additional clinical detail. It also revised terminology, refined the use of consciousness as a classifier, and reduced the number of formally recognized seizure types.^[2]

Classifiers are biologically meaningful categories that directly inform diagnosis and management. These include the main seizure classes (focal, generalized, unknown whether focal or generalized, and unclassified), as well as specific seizure types and the level of consciousness. Descriptors, in contrast, refer to observable or reported features of a seizure, including motor signs, automatisms, sensory symptoms, or affective changes. Although descriptors do not define a seizure type on their own, they provide important context when interpreted alongside clinical data, EEG, and imaging, and may carry therapeutic implications.^[2]

In the basic version of the classification, seizures are described as either with or without observable manifestations. In the expanded version, semiological features may be listed in chronological order, with optional somatotopic modifiers (such as face, arm, or leg) to specify the distribution of clinical signs. This structure supports more precise interpretation and seizure localization.^[2]

The use of consciousness as a classifier replaced the earlier term awareness for focal and unknown seizures. Consciousness is defined as the combination of awareness, assessed after the seizure through recall, and responsiveness, which can be tested during the event using verbal or motor cues. Focal seizures are classified as involving either preserved or impaired consciousness, and this framework also applies to seizures of unknown origin. Generalized seizures are considered to impair consciousness by definition.^[2]

The revision also simplified terminology by removing the word onset from the names of the major seizure classes. As a result, focal-onset seizures became focal seizures, generalized-onset seizures became generalized seizures, and unknown-onset seizures became unknown whether focal or generalized. Other changes include the formal recognition of epileptic negative myoclonus as a seizure manifestation, and the removal of the label nonmotor from absence seizures, which are described without this qualifier. Epileptic spasms remain a seizure type within the generalized seizure class but are also recognized as semiological descriptors that can occur in focal or unknown seizures. Overall, the number of seizure types was reduced from 63 in the 2017 classification to 21 in 2025.^[2]

Descriptors

In the ILAE 2025 classification, descriptors provide additional clinical detail for seizures classified as focal or unknown whether focal or generalized. They are not used for generalized seizures, which are considered biologically complete seizure types. These semiological features are often modified by somatotopic terms (e.g., left hand clonic movement, bilateral asymmetric tonic posturing), and their evolution over time can support localization of the seizure onset zone and identification of specific syndromes. Although additional clinical characteristics, such as seizure triggers, sleep-related onset, or epileptogenic zone, are not formally part of the classification, they remain relevant in clinical and research settings.^[2]

Some focal seizures may present with rare or striking phenomena that, while not formally classified as distinct seizure types, are recognized as semiological descriptors in the ILAE 2025 framework. These include ecstatic or blissful sensations, sexual automatisms, ictal fear or laughter (gelastic seizures), and mystic experiences. Such features often reflect activation of specific brain regions; for instance, ecstatic seizures are typically associated with the anterior insula or mesial temporal structures.^[7]

Unknown and unclassified seizures

For practical reasons, the classification has two categories for seizures that cannot be assigned as focal or generalized:^[2]

• Unknown (for cases where the distinction cannot be made).

• Unclassified (a temporary class, when no further information is available about the seizure).

Tonic-clonic seizures

Tonic-clonic seizures are positioned as a category within each seizure onset type: focal to bilateral tonic-clonic, generalized tonic-clonic, and bilateral tonic-clonic of unknown onset. They are associated with highest morbidity and mortality.^[2]

Epileptic spasms

Epileptic spasms can be generalized, focal, or of unknown onset. Within the generalized class, epileptic spasms are a seizure type, most commonly associated with infantile epileptic spasms syndrome (IESS). In focal and unknown-onset seizures, they are a descriptor within the seizure semiology (e.g., focal epileptic spasm).^[2]

Neonatal seizures

The classification of neonatal seizures (seizures in babies younger than age 4-weeks) is addressed in a separate paper that proposes a classification with emphasis on EEG findings over clinical observation.^[8][2]

Status epilepticus

Status epilepticus is a condition resulting from failure of the mechanisms responsible for seizure termination, or from initiation of mechanisms leading to abnormally prolonged seizures. The ILAE defines two operational time points: time point 1, after which a seizure should be treated, and time point 2, after which long-term consequences including neuronal injury may occur. For tonic-clonic status epilepticus, t1 is five minutes and t2 is 30 minutes.^[9]