Seizure Types and Classification

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There are many different types of seizures. Here we will discuss some of the more well-known seizure types.

Seizures can be divided into three major groups: focal, generalised and unknown. They are classified as such:

  1. Focal Onset
  2. Generalised Onset
  3. Unknown Onset


 
1) Focal Onset Seizures (previously called partial seizures)

About 60% of people with epilepsy have focal onset seizures. Seizure activity starts in one (focal) area of the brain and may spread to other regions of the brain. These seizures can often be subtle or unusual and may go unnoticed or be mistaken for anything from intoxication to daydreaming.

Types of focal onset seizures can be classified by awareness and movement. When the level of awareness is not known, then there is no need to specify it. They are often simply called focal seizures.

Focal seizures can be classified as:

  • Focal aware seizures – awareness is retained (formerly called simple partial seizures)
  • Focal impaired awareness seizures – awareness is altered during any part of the seizure (formerly called complex partial seizures)
  • Focal seizures to a bilateral tonic clonic seizure – this reflects a propagation pattern of a seizure from a focal seizure to a tonic clonic seizure (formerly called secondarily generalised tonic-clonic seizure)
  • Focal aware or impaired awareness seizures may further be sorted by any motor-onset or non-motor-onset symptoms

 
2) Generalised Onset Seizures

Generalised seizures are the result of abnormal activity in both hemispheres of the brain simultaneously. Because of this, consciousness is often lost at the onset of the seizure. Generalised seizures are divided into motor and non-motor (absence) seizures

There are many types of seizures classified as generalised, including:

 
3) Unknown Onset

This is a grouping of seizures that cannot be diagnosed as either focal or generalised and are thus grouped as unknown. Unknown onset seizures are not truly separate types of seizures, but rather placeholders for seizure types for which the onset is unknown. Sometimes this classification is temporary and as more information becomes available over time or through further testing, the type of seizure may be changed to a generalised or focal onset seizure.

This classification of seizures is when a seizure is unable to be classified due to either:

  • inadequate information or
  • an unusual nature of the seizure, or
  • the inability to classify the seizure as either focal or generalised onset.

Seizures of unknown onset may have features may still be classified as:

  • Motor onset
  • Non-motor onset or
  • Unclassified

Most people will only have one or two seizure type(s), which may vary in severity. A person with severe epilepsy or significant damage to the brain may experience a number of different seizure types.
 

Notes:

*Certain seizure types can be either of focal, generalised or unknown onset

Classification of a seizure can stop at any level. For instance, “focal onset” or “generalised onset” seizure with no other elaboration is acceptable. This can be extended to descriptors such as “focal sensory seizure,” “focal motor seizure,” “focal tonic seizure,” or “focal emotional seizure,” and so on.

Bilateral versus generalised: Use the term “bilateral” for tonic–clonic seizures that propagate to both hemispheres and “generalised” for seizures that apparently originate simultaneously in both hemispheres
 

More information

Epileptic seizures explained

Epilepsy seizure types and symptoms, WebMD

Seizure Classification ILAE 2017
 
Videos

Watch here for the most common types of seizures explained