Electroencephalograms (EEGs) are one of the most important tests for epilepsy. The results of an EEG can help diagnose epilepsy or help doctors monitor the effects of starting, changing, or withdrawing your anti-seizure medication.

Epilepsy is a neurological condition involving recurrent seizures that don’t have another known cause.

Read on to learn more about the role that electroencephalograms (EEGs) play in diagnosing and monitoring epilepsy.

Most types of EEG involve placing electrodes on your scalp to evaluate your brain’s electrical activity. Doctors often use EEG after you experience your first seizure to look for changes to your brain activity that are characteristic of epilepsy.

An EEG can only record seizures that occur during the test. It can also potentially pick up atypical brain waves between seizures called interictal epileptiform discharges (IEDs). IEDs are often seen in people with epilepsy, but not always.

Types of EEG used to diagnose or monitor epilepsy include:

Routine EEG

A routine EEG takes about 20–30 minutes. It involves placing about 20 small sensors on your scalp. During the test, you’ll rest quietly and may be asked to open or close your eyes.

Some people might be more likely to have a seizure if they are shown flashing lights. Sometimes doctors use this to trigger a seizure during the EEG on purpose to increase the chances of identifying a seizure focus — which is the area in the brain where the seizure starts.

Sleep EEG

A sleep EEG is performed for about 2 hours while you’re sleeping. Epileptiform activity, or brain wave patterns indicative of epilepsy, is most common during non-rapid eye movement sleep.

A sleep EEG might help reveal atypical activity that doesn’t show up on a routine EEG or help diagnose sleep-related epilepsies.

Sleep-deprived EEG

This involves sleeping for just a few hours at night and then coming in for an EEG the next day or having the test done under conditions of interrupted sleep at a medical facility.

Sleep deprivation can make people who have epilepsy more likely to have a seizure, so it increases the chances that the seizure focus will be identified during the EEG.

Ambulatory EEG

An ambulatory EEG involves recording your brain activity over one or multiple days. You can normally continue to perform most of your daily activities as long as you don’t get the device wet.

Video telemetry

Your doctor may recommend video telemetry if a routine EEG isn’t definitive. This test involves taking a continuous EEG and a video for up to 5 days. The video allows doctors to see the symptoms during or after your seizures, as well as what you were doing before your seizure occurred.

Invasive EEG-telemetry

Invasive EEG-telemetry is similar to ambulatory telemetry, but it requires surgically implanting electrodes into your brain to monitor your brain activity for up to 2 weeks.

Not all seizures show up on an EEG. For example, seizures that begin in the deeper areas of the cerebral cortex often don’t give a clear picture.

A routine EEG can help doctors:

Ambulatory EEG is often recommended for people who have seizures that aren’t well defined with a standard EEG.

Your doctor may recommend video telemetry if your seizures have unusual features to determine:

  • what symptoms you are experiencing during your seizures
  • whether they’re caused by epilepsy
  • what triggers the seizures

Invasive telemetry might be recommended before epilepsy surgery.

Routine EEGs rarely record a seizure. The most common feature that shows up on a routine EEG is interictal epileptiform discharges, which are atypical spikes of electrical information that occur between seizures.

Certain medications, like sedatives, can alter EEG activity, and you might need to have your EEG repeated if you have this test while taking medication that could affect the results.

Scalp EEGs are very safe and there are few, if any, safety concerns. Invasive telemetry comes with a 2–4% chance of developing an infection.

If your EEG will include methods to cause a seizure (such as sleep deprivation or flashing lights), your healthcare team will be ready to administer anti-epilepsy medication if needed.

Your healthcare professional will let you know if there’s anything you’ll have to do to prepare for your test. It’s a good idea to clean and dry your hair before arriving at your appointment to help the sensors stick to your scalp. It’s best to avoid wearing hair gel or wax.

Here’s what you can expect during a routine EEG:

  1. You’ll lie face-up in a reclining chair or bed.
  2. Your technician will measure your head and mark where to put the electrodes on your scalp. They’ll rub a cream on these spots to help the electrodes stick.
  3. The electrodes will be placed on your scalp with an adhesive.
  4. The EEG machine will convert electrical information from your brain into a pattern on a screen.
  5. You may be asked to open or close your eyes, breathe deeply, or look at a flashing light to see if it triggers photosensitive seizures. About 2–5% of people with epilepsy have photosensitive seizures.

Here are some frequently asked questions people have about EEG for epilepsy.

How long is an EEG test for seizures?

A routine EEG usually takes 20–30 minutes. A video EEG can last up to 5 days. An ambulatory EEG can last for days, and a sleep EEG will last for several hours.

How far back can an EEG detect a seizure?

An EEG can only measure seizures that occur during the test. Seizures are rarely recorded during a routine EEG.

How long does it take to get EEG results?

Your recordings will be sent to your doctor, and they will discuss the results with you a few days to weeks later.

What is the average EEG test price?

The non-profit FAIR Health estimates that 80% of people in New York City pay less than $1,671 out-of-network. They estimate that 80% of people pay less than $678 out-of-network in Toledo, Ohio.

Medicare and many other insurance providers cover medically necessary EEGs.

What brain scans are available for epilepsy?

Brain scans that can help diagnose epilepsy include:

An EEG can help doctors identify where in your brain your seizures are occurring and what type of epilepsy you have.

Doctors also use EEGs to see if you’re responding to anti-seizure medications. Routine EEGs take less than an hour, while video telemetry involves continuous monitoring over days.