Understanding the 2017 ILAE Seizure Classification System
In 2017, the International League Against Epilepsy (ILAE) released an updated seizure classification system, refining and expanding the framework originally introduced in 1981. The revised system was designed to improve clinical clarity, diagnostic accuracy, and communication among patients, caregivers, and medical professionals.
Key updates include:
- Reclassification of certain seizure types, with some seizures previously considered generalized now recognized as focal in origin.
- Incorporation of awareness as a defining feature, distinguishing seizures by whether awareness is retained or impaired.
- Emphasis on initial clinical presentation, prioritizing the first observable symptom rather than later manifestations.
- Expanded generalized seizure categories to reflect a broader range of clinical presentations.
- Introduction of an unknown-onset category for seizures in which the point of origin cannot be determined.
- Updated terminology to replace outdated language and improve understanding.
Under the 2017 ILAE framework, seizures are classified according to their point of origin in the brain:
- Focal-onset seizures – originating in one area of the brain
- Generalized-onset seizures – involving both hemispheres from onset
- Unknown-onset seizures – origin cannot be clearly determined
What follows is an overview of common seizure types under this classification system.
Focal-Onset Seizures (Previously Called Partial Seizures)
Focal seizures begin in a specific area of the brain and may remain localized or spread to other regions. They are further categorized based on awareness:
- Focal Aware Seizures – awareness remains intact.
- Focal Impaired Awareness Seizures – awareness is altered or lost.
Types of Focal Seizures
- Focal Motor Seizures – involve abnormal movements such as jerking, twitching, or posturing.
- Focal Non-Motor Seizures – involve sensory, emotional, cognitive, or autonomic changes without prominent movement.
Common Presentations of Focal Seizures
- Auras, including unusual smells, visual disturbances, déjà vu, or rising abdominal sensations
- Autonomic symptoms, such as nausea, changes in heart rate, or sweating
- Emotional manifestations, including sudden fear, anxiety, or euphoria
- Frontal lobe seizures, which may involve complex movements, vocalizations, or behaviors during sleep
- Occipital lobe seizures, often presenting with visual phenomena or temporary vision loss
- Temporal lobe seizures, the most common focal epilepsy type, frequently associated with staring, automatisms, or emotional changes
Generalized-Onset Seizures
Generalized seizures involve both hemispheres of the brain at onset and typically result in impaired awareness or loss of consciousness.
Types of Generalized Seizures
- Absence seizures – brief episodes of staring, usually lasting several seconds
- Atypical absence seizures – similar to absence seizures but with more pronounced motor features
- Myoclonic seizures – sudden, brief muscle jerks
- Tonic seizures – sustained muscle stiffening, often leading to falls
- Clonic seizures – rhythmic, repetitive muscle jerking
- Tonic-clonic seizures – a tonic phase followed by clonic movements
- Atonic seizures – sudden loss of muscle tone, commonly referred to as “drop attacks”
Examples of Generalized Epilepsy Syndromes
- Juvenile Myoclonic Epilepsy, characterized by early-morning myoclonic jerks
- Infantile spasms (West syndrome), typically occurring in infants under one year of age and associated with developmental concerns
- Gelastic seizures, involving inappropriate laughter or crying, often linked to hypothalamic abnormalities
Unknown-Onset Seizures
When the initial point of seizure onset cannot be determined, the seizure is classified as unknown-onset until further diagnostic information becomes available.
- Unknown-onset motor seizures, which may include tonic-clonic features
- Unknown-onset non-motor seizures, involving sensory, autonomic, or cognitive changes
Examples include seizures occurring exclusively during sleep or subtle episodes with minimal outward symptoms that are easily misinterpreted.
Special Seizure Types and Triggers
Some seizures do not fit neatly into standard categories but remain clinically important.
Hormone-Related and Reflex Seizures
- Catamenial epilepsy, in which seizure frequency increases in relation to menstrual cycles
- Photosensitive epilepsy, triggered by flashing or flickering lights
- Reflex epilepsies, provoked by specific stimuli such as reading, music, or tactile input
Seizures Secondary to Other Conditions
- Post-traumatic epilepsy, resulting from head injury or brain trauma
- Eclampsia-related seizures, occurring during pregnancy or the postpartum period
- Withdrawal-related seizures, associated with abrupt cessation of alcohol or certain medications
Diagnosing Seizure Type
Accurate seizure classification requires careful evaluation, often involving multiple diagnostic tools:
- Electroencephalography (EEG) to assess abnormal electrical brain activity
- Magnetic resonance imaging (MRI) or computed tomography (CT) to identify structural abnormalities
- Video EEG monitoring to correlate clinical events with electrical activity
- Genetic testing when inherited epilepsy syndromes are suspected
Consultation with an epileptologist or evaluation at a Level 3 or Level 4 epilepsy center is often recommended for complex cases.
Additional Resources
-
International League Against Epilepsy (ILAE) -
Epilepsy Foundation – Seizure Types -
National Association of Epilepsy Centers
Final Thoughts
A clear understanding of seizure classification supports accurate diagnosis, informed treatment decisions, and improved patient education. The 2017 ILAE update provides a more precise and accessible framework that reflects current scientific understanding.
Individuals experiencing seizures should seek evaluation by a qualified epilepsy specialist to ensure appropriate diagnosis and care.
Disclaimer
The content provided here is for informational purposes only and is not intended to substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional regarding medical concerns or treatment decisions.
David Julian, Natural Vitality Advocate, is not a licensed medical professional. The views expressed are informational in nature and do not guarantee accuracy or completeness.
David Julian is not affiliated with Natural Vitality or NaturalVitality.com and does not promote or sell their products.
