Types of Seizures
According to the International League Against Epilepsy (ILAE) 2017 classification, seizures are fundamentally categorized as focal onset, generalized onset, or unknown onset, with specific subtypes within each category. 1, 2
Focal Onset Seizures
Focal seizures originate within networks of a single cerebral hemisphere and can be further characterized by:
Level of Awareness
- Focal aware (consciousness preserved)
- Focal impaired awareness (consciousness affected)
Motor Symptoms
- Automatisms (repetitive, purposeless movements)
- Atonic (sudden loss of muscle tone)
- Clonic (rhythmic jerking)
- Epileptic spasms (brief contractions of muscles)
- Hyperkinetic (excessive, abnormal movements)
- Myoclonic (brief, shock-like jerks)
- Tonic (sustained muscle contraction)
Non-Motor Symptoms
- Autonomic (changes in autonomic nervous system function)
- Behavior arrest (cessation of movement)
- Cognitive (altered thinking)
- Emotional (fear, anxiety, etc.)
- Sensory (abnormal sensations)
Evolution Pattern
- Focal to bilateral tonic-clonic (previously called "secondarily generalized") 3
Generalized Onset Seizures
Generalized seizures rapidly affect both hemispheres and are divided into:
Motor
- Tonic-clonic (sustained muscle contraction followed by rhythmic jerking)
- Clonic (rhythmic jerking)
- Tonic (sustained muscle contraction)
- Myoclonic (brief muscle jerks)
- Myoclonic-tonic-clonic (myoclonic jerks followed by tonic-clonic activity)
- Myoclonic-atonic (myoclonic jerks followed by loss of muscle tone)
- Atonic (sudden loss of muscle tone)
- Epileptic spasms (brief contractions of muscles)
Non-Motor (Absence)
- Typical absence (brief lapses in awareness with staring)
- Atypical absence (longer episodes with more pronounced changes in tone)
- Myoclonic absence (absence with rhythmic myoclonic movements)
- Eyelid myoclonia (jerking of eyelids during absence) 3
Unknown Onset Seizures
When the beginning of a seizure is not observed or unclear, it may be classified as unknown onset, but can still be described by available features:
- Motor (tonic-clonic, epileptic spasms)
- Non-motor (behavior arrest)
- Unclassified (insufficient information)
Clinical Implications
The classification of seizures is crucial because:
- It guides diagnostic testing and imaging approaches 1
- It determines appropriate medication selection (e.g., carbamazepine for focal seizures and generalized tonic-clonic seizures, but not for absence seizures) 4
- It helps predict prognosis and recurrence risk 5
- It facilitates communication among healthcare providers 1
Diagnostic Considerations
- MRI is superior to CT for identifying epileptogenic lesions, especially for focal seizures 1
- EEG is essential for distinguishing between focal and generalized epilepsies, though some EEG findings can be misleading 6
- Approximately 10% of the population will experience at least one seizure during their lifetime 7
Treatment Approach
Treatment selection depends primarily on seizure type:
- Focal seizures: Carbamazepine, levetiracetam, and other antiepileptic drugs 4, 8
- Generalized seizures: Valproate, lamotrigine, and topiramate are often effective 7
- Absence seizures: Carbamazepine is not effective and should be avoided 4
Important Distinctions
- Provoked vs. Unprovoked: Provoked seizures occur within 7 days of an acute neurological, systemic, metabolic, or toxic insult and are not considered epilepsy by themselves 5
- Epilepsy Definition: Epilepsy is defined as having at least two unprovoked seizures occurring more than 24 hours apart, or one unprovoked seizure with a high risk of recurrence 1, 5
Understanding the specific seizure type is fundamental to proper diagnosis, treatment selection, and patient management in epilepsy care.