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When a fit first happens the person, family or friends are naturally concerned and medical advice, usually from the GP is required immediately. If at all possible, the doctor will want to interview someone who can give a first hand account of the event. The diagnosis depends to a large extent on the description given by someone who has seen the fit or on other information given by the person who has had the fit.

All other tests are not really 'diagnostic' except when a fit is recorded while the person is having an EEG test (see below). Recording a fit during an EEG is very rare, as fits are unpredictable and infrequent in most people. Taking an accurate record of what happened is therefore the most crucial part of the diagnosis and on many occasions making the diagnosis has to be postponed until a reliable witness can be interviewed by a doctor.

Electroencephalography (EEG)
This test is used to record the minute electrical impulses produced by the activity of the brain. The test is carried out in special departments, which are only available in some hospitals. You may be referred to another larger hospital that can carry out the test. During the test, you will be asked to lie or sit in a comfortable chair. A special glue (which can be removed after the test) is used to secure a disc conduction wire to the scalp (see Figure 2 on page 9 of the printed bound version or the pdf version).

The machine only receives signals from the brain and does not itself send any electrical signals. The test is therefore completely harmless. After the wires are connected you will be asked to close your eyes, breath deeply and a strobe light will be used to try to cause seizure activity in the brain. The test takes about 30-45 minutes to complete and sedative drugs are not normally used, except for young children or for people who are confused or find it very difficult to remain still during the test.

Over the years, EEG has developed and it is now possible to combine EEG recording with video so that constant monitoring can take place over several days in a special room. If a fit does occur, then its type and electrical discharge can be recorded at the same time. This combined recording is known as EEG video telemetry. This is particularly useful when the diagnosis is uncertain and if brain surgery for epilepsy is being considered.

The EEG test is not conclusive, and sometimes people with true epilepsy have a normal EEG and those without epilepsy may show some abnormality. The EEG test only records a 20-30 minute period of daily brain activity and may therefore miss an abnormality that is short and sudden. The chance of an EEG showing clear epileptic abnormality in a person with epilepsy is about 50:50. When a diagnosis of epilepsy is strongly suspected, techniques may be used to deliberately cause a fit and the most widely used one is sleep deprivation, where the person is asked to stay awake the night before the test. Lack of sleep is one of the most important triggers of fits in people with epilepsy. As well as being used for epilepsy, the EEG is used to find out about brain function in a number of other illnesses.

Imaging
When a diagnosis of epilepsy is made, the treating doctor also tries to find out what has caused the epilepsy. If damage to the brain or a scar in the brain tissue is the likely cause then imaging will be used to try to find out the exact cause. There are many possible causes of symptomatic epilepsy ranging from birth injuries to congenital malformations of the blood vessels or structure of the brain.

CT and MRI are the two main imaging tests currently used. CT, which stands for Computed Axial Tomography, uses a combination of X-rays and computer technology to provide pictures through sections of the brain. CT is very useful for looking at bone structure, possible underlying causes such as a tumour and for emergencies such as when someone with a head injury has an epileptic fit. It is less useful in the investigation of focal epilepsy as certain subtle changes in brain structure may be missed. Any technique involving X-rays is always used with caution because of the harmful effects of too many X-rays during a lifetime, particularly for children.

MRI (Magnetic Resonance Imaging) uses a large and powerful magnet, microwave radiation and computers to generate detailed images of the inside of the body. The technique does not use X-rays and therefore does not carry any radiation risks. During an MRI scan the person will be asked to lie on a couch which is then moved into a narrow tunnel while the pictures are taken. It is necessary to lie still during the scan, which lasts for 20-40 minutes. The machine makes a loud knocking noise while the pictures are being taken. Some people find lying still in the narrow tube rather claustrophobic and the noise of the machine quite unpleasant. Young children or adults who experience these difficulties can be offered sedation (calming drugs) to help them undergo the test.

Imaging tests are not necessary for every patient with epilepsy. People with primary generalised seizures have normal scans and do not need imaging tests. Some people with partial seizures may need imaging depending on the age the epilepsy started, the type of fit and how well the epilepsy is controlled.

Other tests
Blood tests may sometimes be carried out for people who have been newly diagnosed with epilepsy or for people with chronic partially controlled seizures. These tests may provide information about the possible general causes of the epilepsy and also about the effects of long-term treatment with anti epileptic drugs.

An ECG (electrocardiogram) is occasionally carried out to check if heart problems may be responsible for some of the person's symptoms.The diagnosis of epilepsy is always made with great care as it can have effects on many aspects of the person's life. The effects can include long-term treatment with drugs, change in lifestyle, some changes to work practices, as well as the emotional effect of having a diagnosis of epilepsy. It sometimes takes several weeks before a definite diagnosis is made and anti-epileptic drugs are started. Most GPs do not make a definite diagnosis unless they are sure about the history of the problem and even then, most people will be referred to a specialist for confirmation of the diagnosis.