Epilepsy Diagnosis and Classification

^{Reviewed by: My Child Without Limits Advisory Committee September 2009}

Doctors use a number of different tests to find out if a person has epilepsy, and to learn what kind of seizures he or she experiences. Since there are other disorders that may seem like epilepsy, it's important for the doctor to be certain that the diagnosis is correct.

Some of the tests used to diagnose epilepsy include:

EEG Monitoring

An EEG looks at brain waves. To perform this test, doctors place electrodes, (special sensors) attached to a recording device, on the patient's scalp. This is the most common test for epilepsy because it can tell if there are abnormalities in the brain's electrical activity.

People who have epilepsy often have changes in their normal pattern of brain waves, even when they are not experiencing a seizure. While this type of test can help doctors tell if someone has epilepsy, it is not completely reliable. Some people continue to show normal brain wave patterns even after they have experienced a seizure. In other case, the unusual brain waves are generated deep in the brain where the EEG is unable to see them. Many people who do not have epilepsy also show some unusual brain activity on an EEG.

Whenever possible, an EEG should be performed within 24 hours of a patient's first seizure. It is best if EEGs are performed while the patient is sleeping as well as when he or she is awake, because brain activity during sleep is often quite different than at other times.

Brain Scans

One of the most reliable ways to tell if a person has epilepsy is to use a brain scan. The brain scans used most often include CT (computed tomography), PET (positron emission tomography) and MRI (magnetic resonance imaging). CT and MRI scans let doctors look at the structure of the brain, which can help them find brain tumors, cysts, and other abnormalities. PET and a kind of MRI called functional MRI (fMRI) can be used to check on the brain's activity and detect abnormalities in how it works. SPECT (single photon emission computed tomography) is a fairly new kind of brain scan that is sometimes used to locate the place in the brain where a seizure takes place.

Sometimes doctors may use an experimental type of brain scan called a magnetoencephalogram, or MEG. MEG reads the magnetic signals produced by nerve cells to allow doctors to monitor brain activity. While MEG is similar to EEG, it does not need electrodes and it can find signals from deeper in the brain than an EEG. Doctors also are experimenting with brain scans called magnetic resonance spectroscopy (MRS) that can find abnormalities in the brain's biochemical processes, and with near-infrared spectroscopy, a technique that can detect oxygen levels in brain tissue.

Medical History

Getting a very complete medical history, including symptoms and length of seizures, is still one of the best ways for doctors to tell if a person has epilepsy and what kind of seizures he or she has. The doctor will ask questions about the seizures and any past illnesses or other symptoms a person may have had. Since people who have suffered a seizure often do not remember what happened, speaking with caregivers is also very important.

Blood Tests

Doctors often take blood samples when testing for epilepsy, especially when the patient is a child. These blood samples are tested for disorders that may be associated with the seizures. They also may be used to check for problems like infections, lead poisoning, anemia, and diabetes that may be causing the seizures.

Developmental, Neurological, and Behavioral Tests

Doctors often use tests that measure the patient's movement skills, behavior, and intelligence to learn how the epilepsy is affecting that person. These tests can give the doctor clues about what kind of epilepsy the person has.

Next:

What Are the Different Kinds of Seizures?

Download the Introduction to Epilepsy.