Evoked Potentials Tests
Evoked potentials tests measure the responses of the nervous system. In these tests, the nerves in different sensory pathways are stimulated. This includes vision, hearing, and touch. As an example, nerves involved in the visual pathway may be triggered by flashing lights or different patterns on a screen. The speed at which these nerves respond and how strongly they respond can be measured.1-3
When are evoked potentials tests used for MS?
Receiving an MS diagnosis can be a long and difficult process. An evoked potentials test is not needed to make a diagnosis of MS, but it can be helpful. Some cases of MS are straightforward and only need a physical exam and brain imaging. Others require more information. Evoked potentials tests can lead to diagnosis in more complex cases.
Subclinical nerve damage
In some cases, MS-related nerve damage may be present but not severe enough to cause symptoms. The damage may be so subtle it is not found via neurological exam or on MRI. Evoked potentials tests can be used to detect nerve problems in these cases. Damage that exists but does not yet cause symptoms is called “subclinical.”1
What to expect during an evoked potentials test
Regardless of the type of nerve pathway being tested, the underlying process is the same. Electrodes are placed on the body. These look like small stickers and use a sticky paste to stay attached to your skin. They stimulate nerves and/or measure their responses. The electrodes are removed after the test. Any leftover paste used to attach them to the skin can be washed off.
There is no need to fast (stop eating) before an evoked potentials test. There is also no sedation, either. You may be asked to remove items of clothing and jewelry or metal objects that might get in the way of the test.2,3
Visual evoked potentials
Visual evoked potentials (VEP) tests focus on the nerves involved in vision. Electrodes are placed on the scalp. Then you watch lighted patterns on a screen.2,3 The test may also use flashing lights. As many as 90 percent of those with MS have abnormal VEP test results.1
Auditory evoked potentials
Auditory evoked potentials (AEP) tests focus on the nerves involved in hearing. Electrodes are also placed on the scalp during this test. Clicking noises and other tones are played through headphones. Nerve responses are monitored. Abnormal AEP tests point to problems with the nerves responsible for hearing that travel through the brainstem.2,3
Somatosensory evoked potentials
Somatosensory evoked potentials (SSEP) tests can assess different nerves across the body. Most commonly, these tests focus on the sensory nerves of the arms and legs. These nerves are responsible for perceiving touch and other sensations. Electrodes are placed on the area to give electric stimuli. Common areas for these stimulating electrodes are the knees, wrists, and ankles. More electrodes are placed on the scalp to measure nerve response.2,3
Risks of evoked potentials testing
This is not a complete list of all evoked potentials tests that may be performed. Regardless of the approach used, these tests cause little, if any, discomfort. They are safe and relatively fast to complete. However, as with any test, tell your doctor about all drugs you take and any other medical conditions you have. They can let you know if there are any precautions to take.2