Seizure types

Historical background Descriptions of seizures date back to ancient Mesopotamia. In ~2500 B.C., the Sumerians provided the first writings about seizures. 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." This early classification identified febrile seizures, absence seizures, generalized tonic-clonic seizures, focal seizures, impaired awareness seizures, and status epilepticus. Samuel-Auguste Tissot (1728–1797) authored Traité de l’Epilepsie, a book describing grand état (generalized tonic-clonic seizures) and petit état (absence seizures). Jean-Étienne Dominique Esquirol (1772–1840) later introduced grand mal (generalized tonic-clonic seizures) and petit mal to describe these seizures. In 1937, Gibbs and Lennox introduced psychomotor seizures, seizures with "mental, emotional, motor, and autonomic phenomena." 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. 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. In 2017, the ILAE introduced an operational classification of seizure types. ILAE 2025 revision In 2025, the ILAE released a revised seizure classification that built on the 2017 operational framework. 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. 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. 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. 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. 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. == Focal seizures ==

Focal seizures originate within a network limited to one hemisphere of the brain and may remain confined to that region or propagate to adjacent areas or to the contralateral hemisphere. Despite possible spread, the initial site of onset remains consistent across episodes and defines the seizure as focal. == Generalized seizures ==

Generalized seizures originate in bilateral, distributed brain networks and typically affect both hemispheres from the outset. Although generalized seizures often appear symmetric, some types may have subtle asymmetries in their clinical features or EEG patterns. In the 2025 classification, generalized seizures are defined as a biologically meaningful class and are not subclassified by level of consciousness, as consciousness is presumed to be impaired from onset. In the basic classification, generalized seizures are grouped into three categories: absence seizures, generalized tonic-clonic seizures, and a third group labeled other generalized seizures. The latter is not a biologically distinct category but serves as a grouping term for a variety of seizure types (myoclonic, clonic, tonic, and atonic seizures). == Special considerations ==

Unknown and unclassified seizures For practical reasons, the classification has two categories for seizures that cannot be assigned as focal or generalized: ==References==