ILAE Classification of the Epilepsies

Use the framework to classify the event, then use the syndrome lookup to connect age of onset, seizure type, and EEG pattern.

ILAE 2025 PDF

2025 ILAE Seizure Classification Framework

The 2017 ILAE seizure classification framework was refined in 2025, maintaining the main structure while updating terminology. Consciousness is defined by awareness and responsiveness in the 2025 ILAE update. Classifiers determine the seizure class. Descriptors summarize features such as observable signs and the chronological semiology sequence.

2025 ILAE Seizure Classification at a Glance

Main Class	Consciousness Classifier	Subtypes
Focal	Preserved / Impaired	FPC, FIC, FBTC
Generalized	N/A	GTC, Absence, Myoclonic, Tonic, Clonic, Atonic, Myoclonic-tonic-clonic, Absence-to-tonic-clonic, Generalized negative myoclonic
Unknown	Preserved / Impaired / BTC	Unknown FPC, Unknown FIC, Unknown BTC
Unclassified	N/A	Use when event is confidently epileptic but information insufficient to classify

Abbreviations follow ILAE 2025 Table 1. Neonatal seizures are classified in a separate ILAE position paper and are not included here.

Focal

Focal seizures originate in networks limited to one hemisphere of the brain, with onset consistent from one seizure to another (they may later spread, but initial onset is localized). In the updated classification, focal seizures are further classified by the patient's state of consciousness during the seizure – either preserved or impaired.

Focal Preserved Consciousness (FPC)

A focal seizure in which consciousness remains intact – the person is aware of self and environment and responsive throughout the event. Previously referred to as a focal aware seizure (2017 used "aware or impaired awareness" terminology; "complex partial" is not recommended in current usage).

Patients can often recall the event afterward
May include observable manifestations (autonomic features, motor activity)
Can include non-observable manifestations (sensory, cognitive, emotional)

Focal Impaired Consciousness (FIC)

A focal seizure where consciousness is impaired – the person has diminished awareness and responsiveness. Previously called "complex partial seizure" (2017 used "aware or impaired awareness" terminology; "complex partial" is not recommended in current usage).

Patient may have no memory for the event
May include automatisms (lip smacking, fumbling movements)
Can include observable motor phenomena (posturing, repetitive movements)
Often followed by postictal confusion

Focal-to-Bilateral Tonic-Clonic (FBTC)

A seizure that begins focally and then spreads to involve both hemispheres, resulting in a bilateral tonic-clonic seizure. Formerly called "secondary generalized tonic-clonic."

Always impairs consciousness during the tonic-clonic phase
Typically marked by an initial focal symptom or aura
Progresses to bilateral stiffening and jerking of limbs

Generalized

Generalized seizures originate at some point within, and rapidly engage, bilaterally distributed networks (the seizure activity is widely distributed across networks of the brain at start). Consciousness is typically impaired to some degree in generalized seizures, though for certain brief types awareness may be preserved.

Absence Seizures (AS)

Absence seizures are generalized seizures characterized by brief impairment of consciousness (usually a sudden behavioral arrest and vacant stare). Typically last 5-20 seconds with abrupt onset and offset. Motor features may be present in some absence types.

Typical Absence (TA): Classic absence seen in idiopathic generalized epilepsies with sudden pause, blank stare, and unresponsiveness, usually with 3 Hz generalized spike-wave EEG pattern
Atypical Absence (AA): Less abrupt onset/offset, often longer duration (20-30s), usually in context of Lennox-Gastaut syndrome with slower spike-wave (<2.5 Hz)
Myoclonic Absence (MA): Rhythmic myoclonic jerks accompany typical impairment of consciousness, often lasting 10-60 seconds
Eyelid Myoclonia: Brief bursts of eyelid jerking, often with upward eye deviation, may occur with or without impaired awareness

Generalized Tonic-Clonic Seizures (GTC)

Convulsive seizures featuring a sequence of tonic contraction followed by clonic jerking of the limbs ("grand mal"), with loss of consciousness

Myoclonic-tonic-clonic: GTC seizure beginning with one or more myoclonic jerks
Absence-to-tonic-clonic: GTC seizure that starts with an absence seizure before progressing to convulsion

Other Generalized Seizures

Generalized Myoclonic (GM): Sudden, brief, shock-like muscle jerks involving limbs or body, typically very brief
Generalized Clonic (GC): Rhythmic jerking movements without a preceding tonic phase, more common in infants
Generalized negative myoclonic: Brief losses of muscle tone due to interruption of muscle activity
Generalized Epileptic Spasms (GES): Sudden, brief contraction of axial and proximal muscles, often occurring in clusters
Generalized Tonic (GT): Sustained increase in muscle tone throughout the body, often seen in Lennox-Gastaut syndrome
Generalized Atonic (GA): Sudden loss of muscle tone, may cause drop attacks
Generalized Myoclonic-Atonic (GMA): Two-phase seizure where a myoclonic jerk is immediately followed by an atonic drop

Unknown

This category is used when it is unknown whether a seizure is focal or generalized in onset. Typically, this occurs if a seizure was unwitnessed or lacks sufficient data (e.g. occurred during sleep or without EEG) to determine the initial onset.

Unknown – Preserved Consciousness

A seizure of indeterminate onset during which consciousness was preserved (the person remained aware and responsive).

Used when a patient experiences symptoms without loss of awareness
Unclear if the seizure started focally or was generalized
Less common classification since preserved awareness often suggests focal origin

Unknown – Impaired Consciousness

A seizure of indeterminate onset in which consciousness was impaired. Applies when someone has a loss of awareness during the event but there's no information on how the seizure began.

Person may be found confused or unresponsive
No witness or data indicates whether it was a generalized or focal seizure
Interim classification until further workup clarifies the type

Unknown – Bilateral Tonic-Clonic (BTC)

A generalized tonic-clonic seizure of unknown onset. A convulsive seizure featuring tonic then clonic phases was observed, but it's uncertain if it began focally or was generalized from the start.

Commonly used when seizure onset wasn't witnessed
May be reclassified if subsequent EEG/imaging reveals focal onset
Interim category that should be updated when more information becomes available

Unclassified

Use when an event is confidently epileptic but available information is insufficient to classify. This is an interim category that should be updated when more information becomes available.

Clinical Examples

Examples illustrating the practical application of the 2025 ILAE seizure classification. Abbreviations follow ILAE 2025 Table 1.

Unknown - Bilateral Tonic-Clonic (BTC)

A young woman awakens to find her 20-year-old boyfriend having a seizure in bed. The onset is not witnessed, but she is able to describe bilateral stiffening followed by bilateral "shaking." EEG and MRI findings are normal.

Classification: Bilateral tonic–clonic seizure—unknown whether focal or generalized (BTC)

Focal to Bilateral Tonic-Clonic (FBTC)

In an alternate scenario of the previous case, the EEG shows a clear right parietal slow-wave focus. The MRI shows a right parietal region of cortical dysplasia.

Classification: Focal to bilateral tonic–clonic seizure (FBTC)

Focal - Impaired Consciousness (FIC)

A 25-year-old woman describes seizures beginning with 30s of an intense feeling that "familiar music is playing." She can hear other people talking but afterward realizes that she could not determine what they were saying. Eyewitnesses report that the patient does not respond to external stimuli during the seizure.

Classification: Focal impaired consciousness seizure (FIC)

Evolution: Auditory aura → Receptive aphasia → Impaired responsiveness → Postictal confusion

Focal - Preserved Consciousness (FPC)

A 22-year-old man has seizures during which he remains fully aware, with the "hair on my arms standing on edge" and a feeling of being flushed.

Classification: Focal preserved consciousness seizure (FPC) with observable manifestations: piloerection + flushing

Generalized Myoclonic-Tonic-Clonic

A 13-year-old with juvenile myoclonic epilepsy has seizures beginning with a few jerks, followed by stiffening of all limbs and then rhythmic jerking of all limbs.

Classification: Generalized myoclonic-tonic–clonic seizures (GTC)

Generalized Epileptic Spasm

A 3-month-old boy has clusters of short seizures with flexion in the neck and hips, and abduction in the shoulders of short duration (up to 2s). Video-EEG showed epileptic spasms associated with a generalized suppression on EEG.

Classification: Generalized epileptic spasm (GES)

Focal Epileptic Spasms

A 14-month-old girl has sudden extension of both arms and flexion of the trunk for approximately 2s. These seizures repeat in clusters. EEG shows hypsarrhythmia with bilateral spikes, most prominent over the left parietal region. MRI shows left parietal cortical dysplasia.

Classification: Focal seizure with epileptic spasms (focal epileptic spasms)

FPC with Automatisms

During video-EEG monitoring, a 28-year-old female patient experiences an ascending sensation from the stomach and then starts chewing and manipulating nearby objects using the right hand. The patient can recall what happens and is able to respond.

Classification: Focal preserved consciousness seizure (FPC)

Evolution: Epigastric aura → Oroalimentary automatisms + gestural automatisms with preserved awareness

FBTC with Visual Aura

An 8-year-old boy reports episodes starting with seeing colored dots and stripes on the left side. Eyewitnesses report that he does not respond, turns his head to the left, becomes stiff, and then has jerks in all limbs.

Classification: Focal-to-bilateral tonic–clonic seizure (FBTC)

Evolution: Visual aura → Versive to left + loss of awareness → Bilateral tonic–clonic

FIC with Automatisms

A 33-year-old man experienced seizures accompanied by a feeling of abdominal discomfort followed by loss of awareness. His wife reported episodes of lip smacking, fumbling hand movements, and occasional right-hand posturing.

Classification: Focal impaired consciousness seizure (FIC)

Evolution: Epigastric aura → Impaired awareness → Oroalimentary automatisms + gestural automatisms + dystonic posturing

Examples adapted from the 2025 ILAE Classification of Epileptic Seizures

NeuroLogic: ILAE Classification