In 2017, the International League Against Epilepsy (ILAE) released a new classification of seizure types to make diagnosing and classifying seizures more accurate and easier. Some additional seizure types have also been added allowing flexibility when diagnosing. In this article, you will find the new general outline of seizure classification compared to the old classification formulated in 1981. Additional information can also be accessed through the Epilepsy Foundation internet portal.

Previous Seizure Classification
Seizures were formerly termed as partial or generalised seizures, determined by the area or side of the brain where the seizure first initiated. Partial seizures were further broken down to simple partial or complex partial depending on whether a person is aware or conscious during a seizure. However, this classification system did not acknowledge that some seizure types such as tonic and myoclonic seizures can be either focal or generalised.

New Classification
The new basic classification is based on three key features:

  1. Where seizures begin in the brain;
  2. Level of awareness during a seizure; and
  3. Other features of seizures.

Table 1 below further explains the ILAE 2017 seizure classification system.

Table 1. 2017 Classification of seizure types expanded version

Seizure Type
Features Focal Onset Generalised Onset Unknown Onset
Awareness Aware/impaired awareness
Motor onset AutomatismsAtonic

Clonic

Epileptic spasms

Hyperkinetic

Myoclonic

Tonic

Tonic-clonicClonic

Tonic

Myoclonic

Myoclonic-tonic-clonic

Myoclonic-atonic

Epileptic spasms

Tonic-clonic
Epileptic spasms
Non-motor onset AutonomicBehaviour arrest

Cognitive

Emotional

Sensory

TypicalAtypical

Myoclonic

Eyelid myoclonia

Behaviour arrest
Other Focal to bilateral tonic-clonic TypicalAtypical

Myoclonic

Eyelid myoclonia

Unclassified*

*Seizures may be unclassified due to inadequate information or inability to place in other categories.

1. Where Seizures Begin
Firstly, a health professional should determine the type of seizure based on whether the seizure begins in part of the brain or affects the whole brain at once. Accurate diagnosis of seizure type is crucial to guide the choice of pharmacological treatment, the possibility of surgery, prognosis, and potential causes.

Table 2. Where seizures begin

New Classification Definition  Old Classification
Focal seizures Start in an area or network of cells on one side of the brain Partial seizures
Generalised seizures Involves a network of both sides of the brain at onset Primary generalised
Unknown onset Unknown cause at time of onset but can change once the seizures become clear
Focal to bilateral tonic-clonic seizures A seizure that starts on one side then moves to both sides Secondary generalised tonic-clonic seizures

 

2. Level of Awareness
The new ILAE guidelines split focal seizures into two groups based on the level of awareness during a seizure episode. This is an important distinction as the level of awareness is one of the main factors that affects a person’s safety during a seizure.

Table 3. Level of awareness experienced during seizures

New Classification Definition Old Classification
Focal aware Patient is aware of the seizure Simple partial
Focal impaired awareness Impaired awareness, even if the idea of what is happening is vague Complex partial seizures
Awareness unknown This is due to the absence of an observer
Generalised seizures This type of seizure is documented to affect awareness. Therefore, no further classification was required.

 

3. Other Features
These symptoms can occur during or before the onset of seizures as shown in Table 4.

Table 4. Other features associated with seizures

New Classification Definition Old Classification
Focal motor seizure Movement occurs during seizure event: twitching, jerking or stiffening movement
Focal non-motor seizure Experience other symptoms before onset of seizures, change in sensation and emotions
Generalised motor seizure (tonic-clonic seizures) Seizure characterised by stiffening and jerking movements Grand mal
Generalised non-motor seizure (absence seizures) Seizure characterised by changes in awareness such as staring and repeated movements like lip-smacking Petit mal

 

Unknown Onset Seizures
When the onset of a seizure is not determined, a classification of unknown onset can be applied to seizures with motor and non-motor features. Patients diagnosed with seizures of unknown onset may be reclassified later if the onset of the seizures becomes apparent.

References:

  1. Epilepsy Foundation. 2017 Revised Classification of Seizures. Landover: Epilepsy Foundation of America; 2017.
  2. Fisher R, Saul M. The 2017 ILAR Classification of Seizures. Palo Alto: Stanford Epilepsy Centre; 2017.
  3. Epilepsy Foundation (Greater Chicago). 2017 Revised Classification of Seizures. Chicago: Epilepsy Foundation; 2017.

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