An electroencephalogram (EEG) measures and records the electrical activity in your brain. Your physician may recommend an ambulatory EEG test to get a recording over a few days, as opposed to a few hours. You're not required to stay in the hospital for an ambulatory EEG. You can move around, typically at home.
Why would your doctor recommend an ambulatory EEG?
Your brain's electrical activity changes frequently, and routine EEGs only measure activity over a few minutes. Your Neurologist might suggest an ambulatory EEG to evaluate your brain waves over a few days. This lets your physician to see your brain waves while you're awake and while you're asleep.
Your physician might recommend an ambulatory EEG to diagnose or study Epilepsy or nonepileptic seizures.
It's helpful to study you while you're engaged in your normal day-to-day activities because those events sometimes might serve as triggers for your symptoms.
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.
What to Expect
You'll then lie down on a table where you'll be made to feel warm and comfortable. A technician will measure and mark your head with a grease pencil to ensure the electrodes are put on the proper place. Electrodes connected to EEG wires will be placed on your scalp using a gritty gel followed by a type of paste to affix them. Everything will be covered with gauze and a special cap to ensure the electrodes stay in place.
Some of the testing will take place in the office. You'll be asked to lie quietly, open and close your eyes, answer simple questions and perhaps perform a few mental tasks (such as simple math or spelling). You also may be asked to do a bit of deep breathing, which could make you feel lightheaded or dizzy. This is a normal reaction and will subside once you stop the deep breathing exercises.
You'll then be sent home for 24 to 72 hours. During this time, you'll be attached to a portable monitor. You'll be asked to keep a diary with notes about what you're doing and whether you're experiencing seizures or other symptoms.
Once the test is over, you'll receive instructions on what to do next. You may remove the electrodes at home or have them removed in the office. It takes a bit of work to remove the paste. Once you're back home you'll want to wash your hair to get all the sticky residue out of your hair.
Although the testing is inconvenient, it's non-invasive and not painful.