In March 2017 the International League Against Epilepsy (ILAE), a group of the world's leading epilepsy professionals, introduced a new method to group seizures. This gives doctors a more accurate way to describe a person's seizures, and helps them to prescribe the most appropriate treatments.
Seizures are divided into groups depending on:
- where they start in the brain (onset)
- whether or not a person's awareness is affected
- whether or not seizures involve other symptoms, such as movement
Depending on where they start, seizures are described as being focal onset, generalised onset or unknown onset.
Focal onset seizures
Focal onset seizures start in, and affect, just one part of the brain, sometimes called the 'focus' of the seizures. It might affect a large part of one hemisphere or just a small area in one of the lobes.
Sometimes a focal onset seizure can spread to both sides of the brain (called a focal to bilateral tonic-clonic seizure). The focal onset seizure is then a warning, sometimes called an 'aura' that another seizure will happen.
Levels of awareness
Seizures are also described depending on a person's level of awareness during their seizures; this means whether or not they are aware of the seizure and what is happening around them. These seizures are known as focal aware seizures or focal impaired awareness seizures.
Focal aware seizures (previously called simple partial seizures)
In focal aware seizures (FAS) the person is conscious (aware and alert), will usually know that something is happening and will remember the seizure afterwards.
Some people find their focal aware seizures hard to put into words. During the seizure they may feel ‘strange’ but not be able to describe the feeling afterwards. This may be upsetting or frustrating for them.
Focal impaired awareness seizures (previously called complex partial seizures)
Focal impaired awareness seizures (FIAS) affect a bigger part of one hemisphere (side) of the brain than focal aware seizures.
The person’s consciousness is affected and they may be confused. They might be able to hear you, but not fully understand what you say or be able to respond to you. They may not react as they would normally. If you speak loudly to them, they may think you are being aggressive and so they may react aggressively towards you. FIAS often happen in the temporal lobes but can happen in other parts of the brain.
After the seizure, the person may be confused for a while, sometimes called ‘post-ictal’ (after-seizure) confusion. It may be hard to tell when the seizure has ended. The person might be tired, and want to rest. They may not remember the seizure afterwards.
What happens during focal seizures?
What happens during focal aware and focal impaired awareness seizures depends on where in the brain the seizure happens and what that part of the brain normally does.
Some focal seizures involve movements, called motor symptoms and some involve unusual feelings or sensations called, non-motor symptoms.
Motor symptoms can include:
- making lip-smacking or chewing movements,
- repeatedly picking up objects or pulling at clothes;
- suddenly losing muscle tone and limbs going limp or floppy, or limbs suddenly becoming stiff;
- repetitive jerking movements that affect one or both sides of the body;
- making a loud cry or scream; or
- making strange postures or repetitive movements such as cycling or kicking.
Non-motor symptoms can include:
- changes or a ‘rising’ feeling in the stomach or déjà vu (feeling like you’ve ‘been here before’);
- getting an unusual smell or taste;
- a sudden intense feeling of fear or joy;
- a strange feeling like a ‘wave’ going through the head;
- stiffness or twitching in part of the body, (such as an arm or hand);
- a feeling of numbness or tingling;
- a sensation that an arm or leg feels bigger or smaller than it actually is; or
- visual disturbances such as coloured or flashing lights or hallucinations (seeing something that isn’t actually there).
Sometimes focal seizures spread from one side (hemisphere) to both sides of the brain. This is called a focal to bilateral tonic-clonic seizure.
Focal to bilateral tonic-clonic seizure (previously called a secondarily generalised seizure)
When this happens the person becomes unconscious and will usually have a tonic clonic ('convulsive' or shaking) seizure. If this happens very quickly, they may not be aware that it started as a focal seizure.
Generalised onset seizures
Generalised onset seizures affect both sides of the brain at once and happen without warning.
The person will be unconscious (except in myoclonic seizures), even if just for a few seconds and afterwards will not remember what happened during the seizure.
Tonic clonic seizures
These are the seizures that most people think of as epilepsy.
At the start of the seizure:
- the person becomes unconscious
- their body goes stiff and if they are standing up they usually fall backwards.
- they may cry out
- they may bite their tongue or cheek.
During the seizure:
- they jerk and shake as their muscles relax and tighten rhythmically
- their breathing might be affected and become difficult or sound noisy
- their skin may change colour and become very pale or bluish
- they may wet themselves
After the seizure (once the jerking stops):
- their breathing and colour return to normal
- they may feel tired, confused, have a headache or want to sleep.
Clonic seizures involve repeated rhythmical jerking movements of one side or part of the body or both sides (the whole body) depending on where the seizure starts.
Seizures can start in one part of the brain (called focal motor) or affect both sides of the brain (called generalised clonic).
Tonic and atonic seizures
In a tonic seizure the person’s muscles suddenly become stiff. If they are standing they often fall, usually backwards, and may injure the back of their head. Tonic seizures tend to be very brief and happen without warning.
In an atonic seizure (or ‘drop attack’) the person’s muscles suddenly relax, and they become floppy. If they are standing they often fall, usually forwards, and may injure the front of their head or face. Like tonic seizures, atonic seizures tend to be brief and happen without warning. With both tonic and atonic seizures people usually recover quickly, apart from possible injuries.
Myoclonic means ‘muscle jerk’. Muscle jerks are not always due to epilepsy (for example, some people have them as they fall asleep).
Myoclonic seizures are brief but can happen in clusters (many happening close together in time), and often happen shortly after waking.
In myoclonic seizures the person is conscious, but they are classified as generalised seizures. This is because the person is likely to have other seizures (such as tonic clonic seizures) as well as myoclonic seizures.
Absence seizures (previously called petit-mal) are more common in children than in adults, and can happen very frequently.
During a typical absence the person becomes blank and unresponsive for a few seconds. They may appear to be 'daydreaming'. The seizures may not be noticed because they are brief.
The person may stop what they are doing, look blank and stare, or their eyelids might blink or flutter. They will not respond to what is happening around them. If they are walking they may carry on walking, but will not be aware of what they are doing.
Atypical absences are similar to typical absences (see above) but they start and end more slowly, and last a bit longer than typical absences. As they also include a change in muscle tone, where the limbs go limp or floppy, some people may fall.
Unknown onset seizures
This term is sometimes used to describe a seizure if doctors are not sure where in the brain the seizure starts. This may happen if the person was asleep, alone or the seizure was not witnessed.
If there is not enough information about a person's seizure, or if it is unusual, doctors may call it an unclassified seizure.