ILAE 2025 Seizure Classification Update
The International League Against Epilepsy (ILAE) published an updated seizure classification in April 2025 that retains the core framework from 2017 but introduces six key revisions to improve clinical clarity and practical application. 1, 2
Major Changes from 2017 to 2025
1. Removal of "Onset" Terminology
The term "onset" has been removed from the names of main seizure classes. 2 The classification now uses simpler terminology: focal seizures, generalized seizures, unknown whether focal or generalized, and unclassified seizures rather than "focal onset" or "generalized onset." 1
2. Consciousness Replaces Awareness as Classifier
"Consciousness" is now the preferred term instead of "awareness" and is defined by two components: 1, 2
- Awareness: The patient's ability to recall the event
- Responsiveness: Observable interaction with the environment during the seizure
This dual definition provides more clinical precision than the previous single-dimension "awareness" descriptor used in 2017. 1
3. Observable Features Replace Motor Classification
The 2025 update replaces "motor" seizures with seizures having "observable" features. 2 This change better reflects what can be witnessed during a seizure and acknowledges that not all observable features are strictly motor phenomena. 1 The classification distinguishes between observable and non-observable features throughout the framework. 1
4. Chronological Sequence Emphasis
The updated classification prioritizes the temporal sequence of seizure semiology rather than relying solely on the first-noticed symptom. 2 This represents a shift toward capturing the evolution of seizure manifestations, which has particular importance for surgical planning and localization in the expanded version. 1
5. Epileptic Negative Myoclonus Recognition
Epileptic negative myoclonus is now recognized as a distinct seizure type. 2 This addition addresses a gap in the previous classification system.
6. Epileptic Spasms Reclassification
Epileptic spasms are now used as a descriptor in focal and unknown seizures, while being retained as a seizure type specifically for generalized seizures. 2 This change reflects the recognition that spasms can occur across different seizure categories and require urgent intervention, particularly in infants. 1
Two-Tiered Classification System
Basic Version
The basic classification allows application in resource-limited settings or primary care environments where detailed diagnostic tools may not be available. 1 This version maintains the four main seizure classes and can be used with minimal information.
Expanded Version
The expanded classification provides detailed semiological descriptors with attention to temporal sequence and somatotopic detail, supporting advanced diagnostic and surgical decision-making. 1 This version is intended for specialized epilepsy centers and research applications.
Retained Framework from 2017
The 2025 update maintains the fundamental structure established in 2017: 3, 4
- Focal seizures: Arising within networks of a single cerebral hemisphere, which may remain localized or become more widely distributed 3
- Generalized seizures: Rapidly affecting both hemispheres and both sides of the body 3
- Unknown onset: When seizure onset is unobserved or unclear 4
Focal seizures continue to be characterized by consciousness level and can progress to bilateral tonic-clonic seizures (previously termed "secondarily generalized"). 4
Clinical Implementation Considerations
The 2025 classification received mixed acceptance among neurologists, with only 44.7% expressing favorable opinions and 48.8% still preferring the 2017 version. 5 Epileptologists showed significantly more favorable attitudes (61.9%) compared to general neurologists and neurology residents, who were the most critical subgroup. 5
Despite mixed initial reception, 49.6% of surveyed clinicians expect to adopt the new classification in clinical practice, with 26% undecided. 5 The classification emphasizes that proper seizure identification remains critical because etiologic diagnosis, appropriate treatment, and accurate prognostication all depend on correct classification. 3
The updated system maintains the operational (practical) approach rather than being based on fundamental seizure mechanisms, acknowledging that current knowledge remains insufficient for a purely scientific classification. 3, 4