Newer Classification of Seizures
The International League Against Epilepsy (ILAE) most recently updated the seizure classification in 2025, building upon the 2017 framework, which categorizes seizures into four main classes: Focal, Generalized, Unknown (whether focal or generalized), and Unclassified. 1, 2
Main Seizure Classes
The updated classification removes the term "onset" from the names of main seizure classes and establishes four primary categories 1, 2:
- Focal seizures: Arise within networks of a single cerebral hemisphere and may remain localized or subsequently become more widely distributed 3
- Generalized seizures: Rapidly affect both hemispheres as well as both sides of the body 3
- Unknown (whether focal or generalized): When the origin cannot be determined 1, 2
- Unclassified: When insufficient information exists to classify the seizure 1, 2
Key Changes in the 2025 Update
The 2025 revision introduces six main modifications to improve clinical clarity 2, 4:
- Consciousness replaces awareness as the primary classifier, now defined operationally through both awareness (recall) and responsiveness during the seizure 1, 2, 4
- "Observable" features replace "motor" terminology to better reflect what can be witnessed during a seizure 2, 4
- Chronological sequence of seizure semiology is prioritized over first-noticed symptomatology 2, 4
- Epileptic negative myoclonus is recognized as a new seizure type 1, 2
- Epileptic spasms are now used as a descriptor in focal and unknown seizures, while retained as a seizure type for generalized seizures 2, 4
Focal Seizure Classification
Focal seizures are further characterized by the patient's state of consciousness during the seizure 3:
- Preserved consciousness: Patient maintains awareness and responsiveness 1, 4
- Impaired consciousness: Patient has altered awareness or responsiveness 1, 4
- Undetermined consciousness: When the state cannot be assessed, the seizure remains classified under the parent term "focal seizure" 1
Focal seizures can additionally be described as having motor onset or nonmotor onset symptoms 3
Generalized Seizure Classification
Generalized seizures are subdivided into three main categories 3, 1:
- Absence seizures: Nonmotor generalized seizures 3
- Generalized tonic-clonic seizures: The classic convulsive seizure type 3
- Other generalized seizures: Including tonic, clonic, myoclonic, atonic, and the newly recognized negative myoclonus 1, 2
Clinical Implementation
The classification system distinguishes between classifiers (which reflect biological classes and directly impact clinical management) and descriptors (which indicate other important seizure characteristics) 1, 4. The basic version allows application in resource-limited or primary care environments, while the expanded version offers detailed semiological descriptors for advanced diagnostic and surgical decision-making 4.
Clinical Significance
This operational classification is crucial because etiologic diagnosis, appropriate treatment, and accurate prognostication all depend on correct identification of seizures and epilepsy 3. The classification aims to establish a common language for all healthcare professionals involved in epilepsy care, from resource-limited areas to highly specialized centers 1.
Important Caveats
Despite extensive research, the basic mechanism of epileptic seizures has not been fully elucidated, and as such, the classification remains operational and not based on fundamental mechanisms 3. The 2025 update received mixed feedback from neurologists, with epileptologists being more receptive than general neurologists and neurology residents, though the 2017 version remains the most accepted among practitioners 5.