Why do I need one?
The brain’s electrical activity fluctuates from second to second, but routine EEGs provide only a 20- to 40-minute sample of this activity. If epilepsy waves occur in your brain only once every 3 or 4 hours, or if they only happen at certain times of day, a regular EEG might not record them.
To record seizure activity, a longer EEG recording with times that you are both awake and asleep may be needed. When this test is done at home, it's called an ambulatory EEG. ("Ambulatory" [AM-byew-lah-TOR-ee] means able to walk around.)
An ambulatory EEG may be done if you continue to have seizures after trying various seizure medications. The testing can either confirm the diagnosis of epilepsy or find that epilepsy waves are not causing the seizures. Ambulatory EEG monitoring is generally done at a specialized epilepsy center.
What's the test like?
An ambulatory EEG test makes a recording of your brain's activity over a number of hours or days.
- EEG wires are placed on your scalp, like in a routine EEG, then attached to a special recorder that is slightly larger than a portable cassette player.
- You can wear the recorder on your waist, with the wires running either under your shirt or outside of it.
- The electrodes on your head are covered with a cap or gauze dressing.
- During the test, you can go about your normal routine for up to 24- 72 hours.
- During the test, keep a diary of what you do during the day and if you've had any seizures or other symptoms. This will help the doctor identify the cause of activity on the recording. For instance, the electrodes may make your head itchy, and if you scratch it, that may appear as abnormal activity on the EEG.
- Because the electrodes must stay on your head longer than for a regular EEG, the technologist will probably use a special glue called "collodion" to keep them in place. After the test, acetone (like nail polish removal) or a similar solution is used to remove the glue at the end of the test.
What should I do if I have a seizure during the test?
- Most recorders have an "event" button to press if you have any seizures or different symptoms during the test.
- When the button is pressed, it marks the time on the EEG recording. The doctors can then compare what you feel or what is seen by others to what the EEG shows at the same time.
- If you are not able to press the button during a seizure, someone else can do it for you.
- Newer recorders also have built-in programs to identify epilepsy waves and seizures. Some can even record a video of what happened when the button was pushed.