Seizure types

In the field of neurology, seizure types refer to clinically and electrographically defined categories of seizures, based on observable features, underlying mechanisms, and diagnostic findings. A seizure is a paroxysmal episode of altered behavior, sensation, awareness, or autonomic function resulting from abnormal, excessive, or synchronous neuronal activity in the brain.

Distinguishing between seizure types is important because different types of seizures may have different causes, outcomes, and treatments. The International League Against Epilepsy (ILAE) is the primary body responsible for defining seizure classifications, and the most recent system was published in 2025.

Classification systems

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. 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).

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.

Under the 2025 classification, focal seizures are subdivided into three biologically defined types:

• Focal preserved consciousness seizure (FPC): The person remains aware of and responsive to their environment throughout the event.
• Focal impaired consciousness seizure (FIC): There is diminished awareness and/or responsiveness.
• Focal to bilateral tonic-clonic seizure (FBTC): The seizure begins focally and evolves to involve bilateral tonic-clonic activity.

Focal seizures are inherently diverse in their clinical manifestations, depending on the region involved. These manifestations are described using descriptors, which do not define the seizure type but add critical clinical detail. The ILAE defines two levels of descriptors for focal (and unknown) seizures:

• Basic descriptors: Indicate whether the seizure has observable manifestations or not. Seizures with impaired consciousness are presumed to have observable features.
• Expanded descriptors: Present a chronological sequence of semiological signs, such as automatisms, motor symptoms, sensory phenomena, or speech arrest. These may be further modified using somatotopic terms (e.g., facial clonic movements, right arm tonic posturing) to aid in localization.

Common features of focal seizures include clonic or tonic movements, automatisms (such as lip-smacking or hand fumbling), sensory or visual phenomena, emotional experiences such as fear or déjà vu, and autonomic symptoms like nausea or flushing. These features, when carefully described, contribute to localizing the seizure onset zone and can be used to guide treatment decisions, particularly in presurgical evaluation.

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.

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.

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:

• 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.

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).

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.

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.