Types of seizures

What is a seizure?

A seizure is a short episode of symptoms caused by a burst of abnormal electrical activity in the brain. Typically, a seizure lasts from a few seconds to a few minutes.

Seizures that last longer than 5 minutes, or that repeatedly happen without a recovery period in-between, are a medical emergency. This is also called status epilepticus.

If you have epilepsy, it means that you have had repeated seizures. If you have a single seizure, it does not necessarily mean that you have epilepsy. About 1 in 20 people have a seizure at some time in their lives. It may be the only one that occurs. The definition of epilepsy is more than one seizure.

For more information, see the separate leaflet called Epilepsy and seizures.

Types of epileptic seizures

Seizures are divided into two main types - generalised and focal (used to be called partial). (There are also other uncommon types of seizure.) If you have epilepsy you usually have recurrences of the same type of seizure. However, some people have different types of seizure at different times.

Generalised seizures

These occur if the abnormal electrical activity affects all or most of the brain. Generalised seizures affect both sides of the brain. The symptoms tend to be general and involve much of your body. There are various types of generalised seizure:

• Tonic-clonic seizures (which used to be called grand mal seizures) are the most common type of generalised seizure. With this type of seizure your whole body stiffens, you lose consciousness, and then your body shakes (convulses) due to uncontrollable muscle contractions.

  • This is the type of seizure that most people are familiar with, and is usually what they mean if they simply say 'seizure'.

• Absence seizures (previously sometimes known as petit mal seizures) lead to briefly losing consciousness or awareness. There is no convulsion, you do not fall over and they usually last only seconds. Even though there is no shaking, absence seizures are also 'generalised onset' seizures, because they start in both sides of the brain at the same time. They are more common in children than in adults.

• Myoclonic seizures involve a sudden contraction of the muscles, which causes jerking movements. These can affect the whole body but often occur in just one or both arms.

• Tonic seizures cause a brief loss of consciousness and you may become stiff and fall to the ground.

• Atonic seizures cause you to become limp and to collapse, often with only a brief loss of consciousness.

Focal seizures

In focal seizures the burst of electrical activity starts in, and stays in, one part of the brain. Therefore, you tend to have localised (focal) symptoms. Different parts of the brain control different functions. This means symptoms depend on which part of the brain is affected.

Simple focal seizures are one type. You may have muscular jerks or strange sensations in one arm or leg. You may develop an odd taste, or pins and needles in one part of your body. You do not lose consciousness or awareness.

Complex focal seizures are another type. These can start in any part of the brain. However, they most often begin in one of your two temporal lobes - you have one on each side of your brain behind your temples. If the seizures come from this part of the brain, they are sometimes called temporal lobe epilepsy. Depending on the part of the brain affected, you may behave strangely for a few seconds or minutes. For example, you may fiddle with an object, or mumble, or wander aimlessly. In addition, you may have odd emotions, fears, feelings, visions, or sensations.

Complex focal seizures differ from simple focal seizures in that your consciousness is affected. You may not remember having a seizure.

Sometimes a focal seizure develops into a generalised seizure. This is called a secondary generalised seizure.

Febrile seizures (febrile convulsions)

About 1 in 20 children will have a febrile seizure the time they reach 6 years old. They are most common between the ages of 6 months and 3 years, and are always linked to having a fever (usually due to a viral infection).

Febrile seizures are not preventable, even by reducing a child's temperature using fever-reducing medicines. We don't know exactly why they happen.

Febrile seizures are not the same as epilepsy. Most children who have a febrile seizure will not develop epilepsy, and many will never have another febrile seizure. However, if your child has a 'complex' febrile seizure (which lasts for more than 10 minutes or also involves other symptoms such as weakness on one site of the body) they may have a slightly higher risk of developing epilepsy.

You can find out more from our leaflet called Febrile seizure (Febrile convulsion).

Causes of seizures​

Seizures can have lots of different causes. They include:

• A genetic tendency to have seizures.

  • This is probably the reason for seizures in in most people who have epilepsy; they have likely inherited a combination of different gene variants that make their brain more vulnerable to having a seizure. Many people with epilepsy also have a family history of seizures.

• A genetic condition that causes seizures; these are quite rare but include things such as tuberous sclerosis.

• Injury or damage to the brain, such as:

  • A stroke.

  • A brain tumour.

  • A major head injury.

  • A brain infection such as encephalitis or meningitis.

  • Scarring, or other abnormalities, in an area of the brain. Sometimes people are born with this.

• Fever (most commonly in children - see 'Febrile seizures (febrile convulsions)' above.

• Alcohol misuse. Drinking too much alcohol, and withdrawing from alcohol, can cause seizures.

• Recreational drug use, such as cocaine and ecstasy (MDMA).

• Very low blood glucose (blood sugar).

• Very low blood sodium levels.

People with epilepsy may also have certain triggers that make them more likely to have a seizure, such as:

• Stress.

• Lack of sleep or exhaustion.

• Strobe lights, flickering lights, or bright lights.

• Missing doses of anti-epileptic medication.

• Alcohol or drug use.

See the epilepsy leaflet for more information.

Getting the right diagnosis

It can sometimes be difficult to tell if someone has had a seizure, or if it was something else that looks similar, such as a simple faint.

The most important part of making a diagnosis is to have a clear description of what happened. This is both from the person affected and, if possible, from an eye-witness. Video recordings can also be very helpful.

It can be difficult for a doctor to say definitely that you have had a seizure if the description is not typical. For example, a faint can sometimes cause brief stiffening of the body followed by a few jerks of the arms and legs. This may appear to an onlooker to be a short seizure; however, it is not a seizure. A doctor may ask questions to try to find the cause of what happened. If your doctor is unsure about the cause of the event, you may be referred to a specialist.

If you have a suspected seizure, your doctor should refer you urgently to an epilepsy specialist, aiming for an appointment with two weeks. They should also talk to you about:

• How to recognise another seizure.

• Any steps you can take to cut your chance of another seizure.

• How to keep yourself safe if you have another seizure, and first aid steps to take.

• Who you should contact if you have another seizure while waiting for your specialist appointment.

The specialist and tests

The specialist will want to go over the story of what happened. Below is a list of the sort of questions that you may be asked. Try to go over the answers before your appointment:

• What exactly happened before, during and after the event?

• Did you lose consciousness?

• Were you confused before or after the event?

• Did any parts of your body shake? If so, for how long, and in what way?

• Did you bite your tongue or pass urine?

• How long did it last?

• Did you have any unusual feelings, sensations or emotions before the event?

• Do you have any other symptoms at all, even apparently unrelated?

• Had you taken any alcohol, medicines or street drugs before the event?

• Has anything like this ever happened before?

• Does anyone in the family have epilepsy?

• Have you had any head injuries or illnesses affecting your brain in the past?

• Did you feel well before the event or did you feel poorly, light-headed, hot or distressed?

• Can you think of anything to explain what happened?

It is very helpful to the specialist if a person who saw what happened goes with you to the appointment. Sometimes the specialist can give a cause of the event from the description and examination alone. Sometimes further tests are advised. These may include the following:

• A brain scan - usually a magnetic resonance imaging (MRI) scan or computerised tomography (CT) scan - can show abnormalities affecting the structure of different areas of the brain.

• Electroencephalograph (EEG). This test records the electrical activity of the brain. Special stickers are placed on various parts of the scalp. They are connected to the EEG machine. This amplifies the tiny electrical messages given off by the brain and records their pattern on paper or computer. The test is painless. Some types of seizure produce typical EEG patterns. However, a normal recording does not rule out epilepsy, and not all EEG abnormalities are related to epilepsy.

• Electrocardiogram (ECG). Sometimes abnormal heart rhythms can lead to seizures which can be mistaken for epilepsy. So your doctor may arrange this tracing of your heart.

• Blood tests and other tests may be advised to check on your general well-being. They may also look for other possible causes of the event.

Although helpful, tests are not foolproof. It is possible to have epilepsy with normal test results. Also, if an abnormality is found on a brain scan, it does not prove that it causes seizures. However, tests may help to decide if the event was a seizure or caused by something else.

Sometimes no firm cause can be found to explain the event. A doctor may advise to wait and see if it happens again if there is doubt about the diagnosis.

What if it is a seizure?

Even if a seizure is diagnosed, it may be the only one you ever have. For this reason epilepsy is not usually diagnosed after a single seizure. The definition of epilepsy is recurrent seizures. See the other leaflets in this series for information about the different types of epilepsy.