Evoked potentials tests measure the electrical activity in the brain in response to certain stimuli. The tests stimulate pathways that send information to the brain. For example, nerves involved with the sight pathway may be triggered by flashing lights or patterns on a screen. The speed and strength of how these nerves respond are then measured.1-3
How do evoked potentials tests help diagnose MS?
Getting a diagnosis of MS can be a long and challenging process. An evoked potentials test is not always needed, but it can be helpful. There are several types of MS. Some cases require only a physical exam and brain imaging. Others need further studies. In more complex cases, evoked potentials testing might provide useful diagnostic information.1-3
MS-related nerve damage may be subtle in some people, resulting in little or no symptoms. Damage might be so minor that it goes unnoticed with a brain and nerve (neurological) examination or magnetic resonance imaging (MRI) scan. In situations like this, evoked potentials testing can check for problems with the nerves. Damage that exists but does not yet cause symptoms is called “subclinical.”1
Types of evoked potentials tests
There are several types of evoked potentials tests. They measure sight, sound, and touch.1-3
Visual
Visual evoked potentials (VEP) tests are the most common evoked potentials test used in MS. They measure how quickly and accurately the optic nerve sends visual information to your brain.1-3
During a VEP test, you sit in a chair and stare at a screen. Patterns (usually stripes or checkerboards) flash on the screen. A camera tracks your eye movements. The patterns stimulate a group of nerves that sends messages about what you see from your eye to your brain. Electrodes placed on your head record the resulting electrical impulses.3,4
Swelling (inflammation) and damage of the optic nerve can happen early on in MS. But swelling can also occur with other conditions, so VEP testing is not specific to MS only.1,3,4
Auditory
Auditory evoked potentials (AEP) tests measure how quickly and accurately the auditory nerve sends sound information to your brain. In this test, clicks or tones are played through headphones. The resulting electrical impulses are recorded by electrodes placed on your head.3,5
In MS, balance problems are common. Good balance is needed for everyday activities like standing or walking. The inner ear and auditory nerve affect balance. So, abnormal AEP tests point to auditory nerve problems like those related to MS.3,5
Somatosensory
Somatosensory evoked potentials (SSEP) tests measure how quickly and accurately the spinal cord and brain detect feeling and touch from the body. The test uses electrical stimulation to trigger responses in the nerves. This is usually done with a small electrode placed on the skin.2
During an SSEP test, you lie down on a table. Small electrodes are placed on your skin. The electrodes send painless electrical impulses to different nerves in your body. Then, electrodes placed on your head record the electrical activity in your spinal cord and brain.2
What are the possible side effects of evoked potentials tests?
In general, evoked potentials tests are safe and well-tolerated. Some conditions might interfere with the results of the test, including:2
- Severe nearsightedness (clear up-close vision, blurry vision in the distance)
- Middle ear swelling or ear wax buildup
- Severe hearing impairment
- Head or neck muscle spasms
Things to know about evoked potentials tests
Evoked potentials tests cause little, if any, discomfort. You will not need to fast before the tests. Your doctor can perform the tests in the office or in the hospital. Because these tests are painless, you will not need pain medicine before, during, or after them.2
