Epilepsy is not just one condition, but a group of many different ‘epilepsies’ with one thing in common: a tendency to have seizures that start in the brain. Epilepsy is usually only diagnosed after a person has had more than one seizure. Not all seizures are due to epilepsy. Other conditions that can look like epilepsy include fainting, or very low blood sugar in some people being treated for diabetes. On this page, when we use the term ‘seizure’ we mean epileptic seizure.

Anyone can develop epilepsy, at any time of life. It happens in people of all ages, races and social classes. Epilepsy is most commonly diagnosed in children and in people over 65. There are over half a million people with epilepsy in the UK, so around 1 in 100 people.

Different epilepsies are due to many different underlying causes. The causes can be complex, and sometimes hard to identify. A person might start having seizures because they have one or more of the following.

  • A genetic tendency, passed down from one or both parents (inherited).
  • A genetic tendency that is not inherited, but is a new change in the person’s genes.
  • A structural (sometimes called ‘symptomatic’) change in the brain, such as the brain not developing properly, or damage caused by a brain injury, infections like meningitis, a stroke or a tumour. A brain scan, such as Magnetic Resonance Imaging (MRI), may show this.
  • Structural changes due to genetic conditions such as tuberous sclerosis, or neurofibromatosis, which can cause growths affecting the brain.



What is an EEG?

EEG stands for electroencephalogram, a test used to evaluate and measure the electrical activity in the brain. EEGs use small discs called electrodes that are placed on the scalp. These electrodes pick up tiny electrical impulses in the brain and transmit them via wires to a machine that creates a graph depicting the activity.

When are EEGs used?

EEGs are used to diagnose an array of issues related to the brain, including:

  • epilepsy and other seizure disorders
  • brain tumors
  • encephalopathy (brain dysfunction)
  • encephalitis (brain inflammation)
  • stroke
  • dementia
  • brain injury
  • sleep disorders including apnea

How is an EEG performed?

EEGs are noninvasive and painless. Measurements of the skull are taken first to determine the optimal placement of the electrodes, then the skin in these areas may be carefully cleaned of oils to enable the electrodes to adhere better. In some cases, the electrodes may be attached to a close-fitting cap instead of directly to the scalp. Then, the electrodes are connected to the EEG machine using a series of wires. EEGs may be conducted while the patient is awake or during sleep. During the test, patients may be asked to open and close their eyes, read or perform other simple activities to measure the brain’s activity. EEGs performed on patients who are awake typically take about an hour.

What is an ambulatory EEG?

While “standard” EEGs take about an hour to perform in the office, ambulatory EEGs are performed over a longer period of time, typically a day or more, to enable doctors to gather information about the brain’s activity throughout daily routines and activities. During the test, the patient wears a small portable recording device that’s attached to the electrodes on the scalp. The electrodes are covered with a cap or hat. Patients will be asked to perform their regular routines and to keep a diary of their activities to help the physician identify patterns or issues.

What is a video EEG?

Video EEGs use video monitoring performed at the same time as the EEG to “match” a person’s physical activity during the test. Video EEGs can be very useful in patients with seizures, including those with epilepsy. Video EEGs usually record sounds as well to determine if the patient makes any noises during a seizure or other event.