Absence seizures usually occur only in children and young people. Most people with this type of epilepsy grow out of it by the time they are adults. This leaflet discusses only the type of epilepsy with typical absence seizures. There are other types of 'atypical' absence seizures not dealt with in this leaflet.
This leaflet is part of our series on epilepsy
What is a seizure and what is epilepsy?
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. (Older words for seizures include convulsions and fits.)
The brain contains millions of nerve cells (neurons). Normally, the nerve cells are constantly sending tiny electrical messages down nerves to all parts of the body. Different parts of the brain control different parts and functions of the body. Therefore, the symptoms that occur during a seizure depend on where the burst of electrical activity occurs in the brain. There are different types of seizures but they are broadly divided into two main types - generalised and focal (used to be called partial):
- Generalised seizures: these occur if you have a burst of abnormal electrical activity which spreads throughout the brain. It affects consciousness and may cause a convulsion.
- 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, so symptoms depend on which part of the brain is affected. Focal seizures may not affect consciousness, but may affect sensations, emotions, behaviours, muscles, or combinations of these.
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 person in 20 has a seizure at some time in their life. It may be the only one that occurs. The definition of epilepsy is more than one seizure. The frequency of seizures in people with epilepsy varies. In some cases, there may be years between seizures. At the other extreme, in some cases the seizures occur every day. For others, the frequency of seizures is somewhere in between these extremes.
Epileptic seizures arise from within the brain. A seizure can also be caused by external factors which may affect the brain. For example, a high temperature (fever) may cause a febrile convulsion. Other causes of seizures include lack of oxygen, a low blood sugar level, poisons, and a lot of alcohol. Seizures caused by these external factors are not classed as epilepsy.
What is an absence seizure?
Absence seizure (previously called petit mal) is a form of generalised seizure. It mainly occurs in children and young people. It is uncommon in adults. Many people associate epilepsy with the dramatic convulsive type of seizure. Absence seizures are not like this. They are often not noticed for some time, as it can appear that the affected person is simply daydreaming. The following gives a typical example:
The person has a brief loss of consciousness (an absence) for a few seconds. They do not fall but may pause in what they are doing. Their face often looks pale with a blank expression. They may look dazed, the eyes stare and the eyelids may flutter a little. Sometimes their head may fall down a little, or their arms may shake once or twice. Each seizure usually starts and finishes abruptly. The person is not aware of the absence and resumes what they were doing.
Absence seizures may not be noticed by parents or teachers for some time, as they usually last just a few seconds. It is common to have several absence seizures per day. If they are frequent, a child's education may suffer, as they will not be able to concentrate on lessons.
What causes absence seizures?
No underlying cause can usually be found in the brain. The bursts of abnormal electrical activity usually occur for no apparent reason. Why they start, or continue to occur, is unclear. What seems to happen is that the brain develops a low threshold for bursts of abnormal electrical activity.
In some people, a tendency to develop absence seizures is inherited. How it is passed on is not clear but several members of an extended family may have this type of epilepsy. The parents of children with this type of epilepsy may wish to have genetic counselling to see if there is a chance of further children being affected.
Diagnosing absence seizure epilepsy
The most important part of making a diagnosis is to have a clear description from parents or teachers of what happens during a suspected seizure. Often the description is typical of an absence seizure. However, sometimes it can be difficult for a doctor to be sure. The electroencephalograph (EEG) test is then helpful. This records the electrical impulses from the brain. Special stickers are put on parts of the scalp. They are connected to the EEG machine which amplifies the tiny electrical impulses given off by the brain and records their pattern on paper or a computer. The test is painless. People with absence seizures often have a typical EEG pattern.
Treatment with medicines
There are several different medicines that can control absence seizures. They work by stabilising the electrical activity of the brain. Medication needs to be taken each day to control seizures. In most cases, one medicine can control seizures. A low dose is usually started at first. If this fails to control seizures, the dose may need to be increased or even changed to an alternative medication.
What is the outlook (prognosis)?
The outlook is good. Absence seizures rarely continue into adulthood. This type of epilepsy is not usually associated with any other brain (neurological) condition. Children with this type of epilepsy have the same range of intelligence and other abilities as other children. Treatment usually controls the seizures so that education and other aspects of life can be normal. Treatment can often be stopped in the late teenage years.
About 1 in 3 children with absence seizures will also have one or more convulsive seizures (tonic-clonic seizures). If this occurs, both the absence and convulsive seizures can be treated by the same medication. In this group of children with both types of epilepsy, if treatment is stopped when absence seizures have ceased (often in their late teens), some may develop further convulsive seizures later in life. Treatment may then need to be re-started.
Further help & information
Dr Tim Kenny
Dr Colin Tidy
Prof Cathy Jackson