Seizures classification

Seizures classification

There are lots of different types of epileptic seizure – about 40 in fact. What happens to the person having the seizure varies from one seizure to another and from one person to another. Although seizures vary, it is often useful to classify or group seizures together by similar features. Here we look at the different types of seizures and how they are classified.

ILAE classification

When we classify seizures, we usually follow the International League Against Epilepsy (ILAE) classification, which groups seizures together by what they look like and what happens to the person. There are also other types of classification that group seizures together by the cause of the epilepsy.

Although what happens during a seizure can vary, most seizures have several things in common. Most are spontaneous (happen without a known trigger or cause), sudden (happen without a warning, out of the blue), short-lived (lasting a few seconds or minutes), and stop on their own without medical help.

Why do seizures vary?

Different parts of our brains do different things. See the first back 2 basics for a description of what different parts of the brain do.

What happens to someone when they have a seizure varies depending on which part of the brain is affected by the seizure, and what that part of the brain normally does. This is why seizures vary, and cause different “symptoms”.

The descriptions of seizures that follow give the ‘typical’ features of the seizure, but everyone’s seizures can be different, and may not exactly fit the descriptions.

To start with, seizures are usually classified into partial or generalised seizures.

Partial seizures

In partial seizures the seizure happens in, and affects, just one part of the brain. This could be any part of the brain, and what happens to the person depends on which part of the brain is affected and how big the affected area is.

Simple partial seizures

If the area of the brain affected by the seizure is small, this is called a simple partial seizure (SPS). The person will be awake and aware during the seizure and will remember what happened to them.

Temporal lobe SPS are the most common type of SPS. Symptoms can include:

• an 'epigastric rising sensation' (which is like the feeling you get at the top of a fairground ride where you “leave your tummy at the top”)
• déjà vu (the feeling of 'having been here before') or jamais vu (where familiar things seem new)
• a flashback of memory
• a sudden, intense feeling of fear or joy
• a funny taste or smell.

Frontal lobe SPS can be harder to put into words. Some people experience:

• strange movements
• a feeling of a wave going through the head or body
• stiffness or jerking of part of the body that might start in one place, for example the face, and spread to other parts of the body.

Parietal lobe SPS often include strange sensations such as

• numbness or tingling
• burning sensations or a feeling of heat
• a feeling that part of the body, an arm or leg, is bigger or smaller than they really are.

Occipital lobe SPS involve visual sensations, such as:

• distortion or loss of vision
• seeing flashing lights or coloured shapes

• seeing people or objects that are not there (hallucinations).

Complex partial seizures

If the area of the brain affected by the seizure is larger than in an SPS, this causes a complex partial seizure (CPS). These seizures affect three things – the person’s awareness (they will be only partly conscious), their accessibility (they may not be able to respond to you) and their memory (they may not remember most or all of the seizure).

Temporal lobe CPS is the most common CPS. Often people experience:

• automatisms such as lip-smacking or chewing movements, or rubbing, stroking or fiddling with their hands; or
• looking from one side to another in a confused way.

This type of CPS usually lasts around 2–3 minutes (about the length of a song on the radio) and then it takes the person 5–10 minutes to come around. They are often confused.

Frontal lobe CPS are often much shorter then temporal lobe CPS, usually lasting about 15–30 seconds (about as long as a TV advert). During the seizures the person might:

• make strange postures with their arms or legs; or
• make juddering movements.

Afterwards the person will usually recover quite quickly.

Generalised seizures

In generalised seizures the seizure affects all of the brain all at once. Generalised seizures affect the person’s consciousness so that they lose consciousness, even just for a few seconds. Because of this, after the seizure, they will have no memory of the seizure.

Tonic clonic seizures

These are the seizures that we usually think of as epilepsy. There are two parts to this seizure. In the tonic part, all the muscles in the person’s body ‘contract’ and go stiff. If they are standing up they will fall down. Because the muscles around the chest go stiff, this pushes air out of the lungs and the person may cry out. Also they might bite their tongue as the seizure starts.

The next part of the seizure is the clonic, jerking or convulsing part. This might last for a couple of minutes. The muscles go stiff and then relax, stiff and relax repeatedly. This makes the person’s arms and legs jerk. Often the person’s breathing is affected. They might grunt or snort or sound as if it is difficult to breathe, and they may go very pale in colour or slightly blue around the lips. This is because the muscles around the rib cage that help us to breathe are contracting and relaxing too.

The seizure stops when all the jerking stops. The person will then relax and go floppy, and start to breathe normally again. They might feel tired and sleepy. They might also be confused, have a headache and want to sleep. Some people say it feels like they have run a marathon in a couple of minutes - that’s how tired they are.

Tonic seizures

Tonic seizures happen when all the muscles in the person’s body go stiff. They become rigid and will fall down, usually backwards: a bit like a tree being cut down. These seizures tend to be very quick and the person comes round from them quickly.

Atonic seizures

Atonic seizures are the opposite of tonic seizures and all the muscles in the body suddenly go floppy. When this happens the person will fall down, usually forwards (like a puppet whose strings have been cut). These seizures are also called ‘drop attacks’ as they cause the person to suddenly drop to the ground. Like tonic seizures the person usually recovers quickly, but they may hurt themselves when they fall.

Myoclonic seizures

‘Myoclonic’ means ‘muscle jerk’, which describes what happens during these seizures. Usually the arms or leg will briefly jerk, although it can be the head or trunk (top half of the body). These jerks are similar to the jerks we all have just as we are falling off to sleep (hypnagogic jerk), but they happen at other times during the day, often during the first few hours after waking- up. Usually the person recovers quickly.

Absence seizures

Absences are brief seizures where the person is ‘absent’ for a couple of seconds, going blank and staring. The seizures can be quite subtle and hard to see, as there may be no obvious movement. If the person is talking, they will usually pause in the middle of what they are saying, but if they are walking around they might carry on walking. During the seizure they are unconscious – if you talk to them they will not respond.

Absences tend to be more frequent in children, but can still happen in adults. Some children can have hundreds of absences every day, which can cause a lot of disruption to their life. Imagine you are watching your favourite TV programme and keep ‘blanking-out’ and missing bits of information.

Absences can be confused with daydreaming. If you talk to someone who is daydreaming, they will usually respond to you but this is not so with absences. Also, if the ‘blank spells’ happen when the person is doing something they enjoy, such as talking or playing a game, then they are less likely to be daydreaming.

Some absences last longer than a few seconds and involve some movement of the body, such as jerking of the shoulders. These seizures are known as atypical absences and tend to happen in people with learning disabilities, who may have other types of seizures as well.

Secondarily generalised seizures

Sometimes a partial seizure can become a generalised seizure and is called a secondarily generalised seizure (as it starts out as a partial seizure and becomes generalised in the second part of the seizure). The most common type of generalised seizure to happen in this case is a tonic clonic seizure.

As the seizure starts as a simple or complex partial seizure, the person might be aware that the seizure has started, but as it becomes generalised, they will lose consciousness.

Unclassified seizures

Some seizures do not easily fit into one of the categories here; they might have different parts of different seizures, or they can be unique to the person having them. These seizures are sometimes called ‘unclassified’. As more is known about what happens during the seizure, if might be possible to classify them later on.

Asleep seizures

If someone has seizures while they are asleep, they may be called 'asleep' or ‘nocturnal’ seizures. The seizures could also happen during the day if the person falls asleep. Asleep seizures do not describe what type of seizure the person has, it only tells you when the seizures happen.

Why classify seizures at all?

There are lots of reasons why it is useful to classify seizures and to know the type of seizure someone has: we can identify where in the brain the seizures happen (which might be useful for considering surgery); we can understand why someone is behaving the way they are during a seizure; and it can help to tell us how to help the person during their seizures. But perhaps the most useful reason for classifying seizures is because this helps when considering medication for epilepsy as some antiepileptic drugs work on certain types of seizures and not on other types.

© Epilepsy Society
October 2006