How Seizures Are Classified
Epilepsy is a neurological (brain) disease in which someone has repeated seizures.
In 2017, doctors around the world adopted a new way of talking about seizures. The International League Against Epilepsy (ILAE) announced that going forward seizures would be named, or classified, according to 3 features:1
- Where seizures begin in the brain
- Level of awareness during a seizure
- Other features
The new system helps doctors decide on the types of testing, treatment, and long-term outlook for someone with a certain class of seizure. These standard classifications also help researchers who work on epilepsy. Finally, the new system gives people with epilepsy a way to describe their seizures.
Epilepsy names before 2017
Before 2017, the most common names for seizures were “grand mal” and “petit mal.” This loosely meant big seizures (shaking, falling) or little seizures (stares). Then, the terms “partial” and “generalized” were added.1
Partial meant seizures that start on 1 side of the brain. The person having them remained aware or somewhat aware. Generalized meant seizures that started on both sides of the brain at the same time.1
This old system did not accurately describe many types of seizures.
How seizures are classified today
When someone is first diagnosed with epilepsy, their doctor will conduct an exam. They will also run tests and talk to the person with epilepsy and people who have seen their seizures. Information from these sources will help the doctor decide what kind of seizures the person is having. Naming, or classifying, the seizures helps guide treatment.1
How are seizures classified?
By where seizures begin
Where seizures begin in the brain gives doctors their first clue. The starting location of seizures is described as:1
- Generalized seizures (or primary generalized seizures) are seizures that begin on both sides of the brain at the same time.
- Focal seizures (or partial seizures) are seizures that begin on 1 side of the brain.
- Focal-to-bilateral onset seizures (secondary generalized seizures) are seizures that start in 1 part of the brain and spread to both sides.
- Unknown onset seizures have an unknown origin. This can be because the seizures happen during sleep or the person lives alone, so no one else sees the seizures. This label may change if doctors learn later where someone’s seizures start.
Where a seizure begins is important because it gives doctors a clue about which medicines and surgeries may control the seizures. It also gives doctors an idea of long-term outcomes and possible causes.1
Next, doctors look at whether a person is aware of their surroundings during a seizure. This is important because it affects the person’s safety during a seizure. Names to describe awareness during seizures include:1
- Focal aware seizure (simple partial seizure), a seizure in which someone remains aware even if they are not able to talk or respond to questions.
- Focal impaired awareness seizure (complex partial seizure), a seizure in which someone is unaware at any time during the seizure. They only have a vague idea of what happened.
- Awareness unknown seizure, a seizure in which doctors cannot tell if a person is aware during their seizures. This may happen if the seizures happen during sleep or if the person lives alone.
If someone has generalized seizures, there is no classification added for awareness. Being unaware or unconscious is part of a generalized seizure.
By type of movement – focal seizures
Doctors also look at what kind of movement someone has during their seizures. With focal seizures, the classifications include:1
- Focal motor seizures involve some type of movement that happens during the seizure. This may be twitching, jerking, stiffening, licking lips, rubbing hands, walking, or running.
- Focal non-motor seizures involve changes in smell, taste, emotions, and/or thinking.
- Aura seizures involve early symptoms felt at the beginning of a seizure. Some people describe these as warnings that a seizure is about to happen. This warning is called an aura.
Both focal aware and focal impaired awareness seizures can have motor or non-motor classifications added.
By type of movement – generalized seizures
Generalized seizures (those that start on both sides of the brain) can also be classified by type of movement:1
- Generalized tonic-clonic seizures (grand mal seizures) cause stiffening (tonic phase) and then jerking (clonic phase).
- Absence seizures (petit mal seizures) cause you to stare, repeat movements such as lip-smacking, and have short changes in awareness.
Even if doctors do not know whether seizures are focal or generalized, they can still classify the seizures as motor (movement) or non-motor (no movement):1
- Unknown motor seizures are called tonic-clonic or epileptic spasms.
- Unknown non-motor seizures are called behavior arrest seizures.
A person’s seizures may be unclassified if doctors do not have enough information to place the seizures in another category.