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.
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 partial:
Generalised seizures. These occur if you have a burst of abnormal electrical activity which affects the whole of the brain. It affects consciousness, and may cause a convulsion.
Partial seizures are also called focal seizures. In these types of 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. Partial seizures may not affect consciousness, and may affect sensations, emotions, behaviours, muscles, or combinations of these.
What is epilepsy?
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 life. It may be the only one that occurs. The definition of epilepsy is more than one seizure.
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 fever may cause a febrile convulsion.
Other causes of seizures include: lack of oxygen, a low blood sugar level, certain drugs, poisons and a lot of alcohol. Seizures caused by these external factors are not classed as epilepsy.
Getting the right diagnosis
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.
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, but 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.
Diagnosing Seizures & Epilepsy
It can be extremely difficult to diagnose a seizure. Because physicians are rarely able to witness a seizure during a clinic visit, it is vital to have an accurate history of the event or events that have occurred.
While many people with seizures or epilepsy have abnormal EEGs, many do not. There are a number of additional tests that help doctors identify the type of seizure and its effects.
Diagnostic services available to our patients on site and in collaboration with referring physicians include:
- Complete neurological consultation for epilepsy and related conditions
- Neurophysiological tests, including routine EEGs and outpatient and inpatient video-EEG monitoring
- Long-term inpatient video-EEG monitoring with scalp or intracranial electrodes
- Neuroimaging: MRI, MRS, PET, fMRI
- Speech and auditory processing evaluations
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?
Reasons for tests
Man having an MRI scanYour neurologist may ask you to have some tests to get extra information about your seizures. The tests are usually done by a technician (a person who is trained to do them).
The results from the tests are then passed back to the neurologist to see what they show. The results may indicate that you have epilepsy and may also show a cause for your epilepsy.
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) or computed tomography (CT) scan – can show abnormalities affecting the structure of different parts of the brain.
- Electroencephalogram (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.
- 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.
Other leaflets in this series provide information about different types of epilepsy.