The EEG (electroencephalograph) is the most common diagnostic test for epilepsy. It is used to detect abnormalities in the brain's electrical activity. People with epilepsy frequently have changes in their normal pattern of brain waves, even when they are not experiencing a seizure. Whenever possible, an EEG should be performed within 24 hours of a person’s first seizure.
The EEG machine—short for electroencephalograph—records electrical activity from your brain. This allows your neurologist to see your brain waves. When a person has epilepsy, the EEG shows a special pattern of spikes and waves which will define the seizure type. Knowing this, a neurologist can prescribe treatment that will most likely control the epilepsy. Learn more about epilepsy treatment options.
Sometimes your neurologist will order a "sleep-deprived EEG." That's because lack of sleep tends to bring out the worst in brain waves. By staying up all night, you are increasing the chance that epileptic activity will appear, if it exists. This information can help your neurologist choose your medication or see if your seizures are likely to return. It only makes sense that people with epilepsy need to get plenty of sleep!
During this process, a bright light is flashed in your eyes during an EEG. This is to see if you have photosensitive epilepsy. Only 5% of people with seizures have this type, but it's best to rule it out. These seizures can occur from some flashing lights, television, and computer games.
During an EEG, you may be asked to hyperventilate by taking deep breaths for 3 to 5 minutes. For reasons that are not fully understood, this can bring out epileptic activity. This allows some people to find out a lot about the inner workings of their brain.
In some cases, your neurologist may order additional tests, even though you’ve already had an EEG. This is because each test tells your neurologist something different about your brain and how it works. So, while an EEG is the best way to find out about brain waves, it doesn’t provide the most accurate picture of the inside of the brain. If your neurologist needs to see the inside of your brain to make a diagnosis, an MRI (Magnetic Resonance Imaging) offers the best results. A CAT (computerized axial tomography) scan is another excellent way to see inside the brain. In cases where your EEG results are abnormal, an MRI or CAT scan can help clarify your brain’s functioning.
A CAT scan takes thousands of x-ray images and uses them, with the help of a powerful computer, to form a picture of the brain. CAT scans can be performed very quickly and are often used in cases where a brain injury is suspected.
An MRI also uses a computer, but instead of x-rays, it uses a strong magnetic field to form a highly-detailed image of the brain. Neurologists who specialize in epilepsy use the MRI to look for subtle abnormalities in the brain that can cause seizures.
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