NeuroLogic: ILAE Classification
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. For the board-level read of the 2022 framework, start in Board Review Part III. For ICU EEG terms, use EEG Fundamentals.
ILAE 2025 PDFThe diagnostic path: three levels, plus etiology
The ILAE framework is not a list — it is an order of questions. Each level answers something the one before it cannot, and etiology is asked throughout.
Level 1 — What kind of seizure was it?
Classify the event using the 2025 seizure classes, then describe what happened in sequence.
- Focal — begins within one hemisphere. If assessable, classify consciousness as preserved or impaired using both awareness and responsiveness. Spread to a bilateral convulsion is focal to bilateral tonic–clonic.
- Generalized — rapidly engages networks on both sides. Consciousness is not a classifier in this group.
- Unknown whether focal or generalized — some features are known, but the available evidence does not distinguish these classes.
- Unclassified — the event is considered epileptic, but there is insufficient information to characterize it.
Describe observable and non-observable manifestations in chronological order. If consciousness cannot be determined, retain the parent class; do not guess. The 2017 awareness and motor/non-motor labels are historical terminology.
Level 2 — What kind of epilepsy does the person have?
A different question from Level 1: this classifies the disease, not the event, and it assumes a diagnosis of epilepsy has already been made. Someone can have focal seizures and still not have focal epilepsy.
- Focal epilepsy — focal seizures. EEG often shows focal interictal epileptiform discharges and may be normal.
- Generalized epilepsy — generalized seizure types, typically with generalized spike–wave on EEG.
- Combined generalized and focal epilepsy — both types genuinely occur in the same person. Dravet syndrome and Lennox–Gastaut syndrome sit here. This category did not exist before 2017 and is often the one that gets missed.
- Unknown epilepsy type — epilepsy is established but the information to type it is not available.
At Level 2, medication choice depends on seizure types as well as epilepsy type. Carbamazepine and oxcarbazepine can aggravate absence or myoclonic seizures; this is not a uniform effect of every medication with sodium-channel activity.
Level 3 — Does it fit a syndrome?
A syndrome is a recognisable cluster that travels together: seizure types, EEG and imaging features, an age-dependent pattern of onset and often of remission, plus triggers, diurnal variation, and characteristic comorbidities.
A syndrome diagnosis buys you things the first two levels cannot: expected course, specific drug choices and drugs to avoid, genetic counselling, and a prognosis to give the family. Not every epilepsy fits one, and saying so is better than forcing a label.
Etiology — asked from the first visit, not last
Etiology is not a fourth step. It runs alongside all three levels and is reconsidered as information arrives. More than one category can apply at once.
- Structural — a lesion on imaging that plausibly explains the seizures. The category that opens the door to surgery.
- Genetic — from a known pathogenic variant to a presumed polygenic basis. Directs precision treatment and family counselling.
- Infectious — epilepsy resulting from a CNS infection. Neurocysticercosis is the commonest cause of epilepsy worldwide.
- Metabolic — an established metabolic disorder. Some are treatable in a way nothing else is, such as ketogenic dietary therapy in GLUT1 deficiency, or pyridoxine-dependent epilepsy.
- Immune — autoimmune-mediated CNS inflammation. Points to immunotherapy rather than escalating antiseizure medication.
- Unknown — the cause has not been found. Still a diagnosis, and still worth revisiting.
Comorbidities are considered at every level too — learning, developmental, psychiatric and behavioral. In several syndromes they, not the seizures, determine long-term outcome.
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 | Absence (TA, AA, MA, EMA); GTC (including myoclonic tonic-clonic and absence-to-tonic-clonic); GM, GC, GNM, GES, GT, GA, GMA |
| Unknown | Preserved / Impaired, when assessable | Preserved consciousness (PC), impaired consciousness (IC), bilateral tonic-clonic (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 with preserved awareness and responsiveness. Ask about later recall and responses during the event, compared with the person's baseline. Consider aphasia, paresis, or isolated amnesia before interpreting a failed response or memory gap. The 2017 term was “focal aware seizure”; the older term “simple partial seizure” is no longer recommended.
- Document how awareness and responsiveness were assessed
- May include observable manifestations (autonomic features, motor activity)
- Can include non-observable manifestations (sensory, cognitive, emotional)
Focal Impaired Consciousness (FIC)
A focal seizure with impaired awareness or impaired responsiveness at any point during the seizure, after considering alternative explanations such as aphasia or paresis. The 2017 term was “focal impaired-awareness seizure”; the older term “complex partial seizure” is no longer recommended.
- Memory may be incomplete, but amnesia is not required for classification
- May include automatisms (lip smacking, fumbling movements)
- Can include observable motor phenomena (posturing, repetitive movements)
- Postictal confusion may occur but is not required
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
- An initial focal symptom may occur, but a recalled aura is not required
- 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)
Unknown-onset bilateral tonic-clonic (BTC). A convulsive seizure featuring tonic then clonic phases was observed, but it is uncertain whether 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.
Examples adapted from the 2025 ILAE Classification of Epileptic Seizures. Terminology reviewed September 2026.