What is the latest classification of seizures?

Latest Classification of Seizures According to the International League Against Epilepsy (ILAE) 2017

The most recent classification of seizures was established by the International League Against Epilepsy (ILAE) in 2017, which categorizes seizures into three fundamental types: focal onset, generalized onset, and unknown onset. 1, 2

Basic Classification Framework

• Seizures are classified based on their origin in the brain, not on fundamental mechanisms, as the basic mechanism of epileptic seizures has not been fully elucidated 1
• The classification is operational (practical) rather than scientifically based due to current knowledge limitations 2
• Correct seizure classification is crucial for proper diagnosis, treatment selection, and accurate prognostication 1

Primary Seizure Types

1. Focal Onset Seizures

• Arise within networks of a single cerebral hemisphere and may remain localized or become more widely distributed 1, 2
• Can be optionally subclassified by awareness level:
  • Focal aware seizures (previously "simple partial") 2, 3
  • Focal impaired awareness seizures (previously "complex partial") 2, 3
• Further characterized by motor or non-motor onset symptoms:
  • Motor onset: atonic, automatisms, clonic, epileptic spasms, hyperkinetic, myoclonic, or tonic 4, 3
  • Non-motor onset: autonomic, behavior arrest, cognitive, emotional, or sensory 4, 3
• Can evolve to "focal to bilateral tonic-clonic seizures" (previously "secondarily generalized seizures") 2, 3

2. Generalized Onset Seizures

• Rapidly affect both hemispheres and both sides of the body from onset 1, 2
• Subdivided into:
  • Motor: tonic-clonic, clonic, tonic, myoclonic, myoclonic-tonic-clonic, myoclonic-atonic, atonic, epileptic spasms 4, 3
  • Non-motor (absence): typical, atypical, myoclonic absence, absence with eyelid myoclonia 4, 2

3. Unknown Onset Seizures

• Used when the onset is not observed or unclear 2, 5
• Can still be classified by available features as:
  • Motor (tonic-clonic, epileptic spasms, or other motor)
  • Non-motor
  • Unclassified 3, 5

Key Changes from Previous Classifications

• Terminology changes: "partial" seizures are now called "focal" seizures 2
• Eliminated terms: dyscognitive, simple partial, complex partial, psychic, and secondarily generalized 2
• New focal seizure types include automatisms, behavior arrest, hyperkinetic, autonomic, cognitive, and emotional 2
• Some seizure types can now be classified as either focal or generalized: atonic, clonic, epileptic spasms, myoclonic, and tonic 2
• New generalized seizure types: absence with eyelid myoclonia, myoclonic absence, myoclonic-atonic, myoclonic-tonic-clonic 2

Clinical Application

• The earliest prominent manifestation defines the seizure type, which might then progress to other signs and symptoms 3
• Both basic and extended versions of the classification are available depending on the desired level of detail 3
• The classification allows greater flexibility and transparency in naming seizure types 2
• Proper identification of seizure type is essential for selecting appropriate treatment and determining prognosis 1, 5

Epilepsy Classification

• Epilepsy is defined as having at least two unprovoked seizures occurring more than 24 hours apart, one unprovoked seizure with high recurrence risk, or diagnosis of an epilepsy syndrome 1, 6
• Epilepsies can be classified as focal, generalized, combined generalized and focal, or unknown 5
• The concept of epilepsy syndrome refers to a cluster of features incorporating seizure types, EEG findings, imaging results, and other features including genetics 5
• The new classification system emphasizes the etiology of seizures and epilepsies 5, 7

Pitfalls and Caveats

• Classification is based on clinical semiology rather than underlying pathophysiology 1, 7
• Some seizures may have features of both focal and generalized onset, making classification challenging 2
• Proper classification requires careful observation of seizure onset, which may be missed in clinical settings 3
• The classification system continues to evolve as understanding of epilepsy mechanisms improves 7