Evoked potentials

An evoked potentials test measures the speed of the messages along your sensory nerves to the brain. Evoked potentials tests are sometimes used in the diagnosis of MS, because they are painless, non-invasive and faster than MRI scans. Although MRI scans are more commonly used, there is still a role for evoked potentials tests, particularly at the earlier stages of MS.

Your brain produces electrical current in response to information that comes in through your senses. This current can be detected on your scalp, using electrodes attached with sticky pads. As damage to the nerves in MS can slow down the transmission of nerve signals, evoked potential tests can indicate nerve pathways that are damaged, even before you notice any clinical symptoms. Delays of as little as 10 milliseconds can indicate that there is damage to the nerve pathway.

Types of evoked potentials tests

The most commonly used test is called visual evoked potentials (VEP), which measures how long it takes the brain to respond to messages sent by the eyes. Your neurologist may also suggest running an auditory evoked potential test which tests your hearing using clicks that you listen to through headphones. Another alternative is a somatosensory evoked potential, which tests your skin sensation using tiny electrical shocks. 

If you have a VEP test, you will be shown a flashing chessboard pattern on a computer screen. The electrodes on your scalp will detect brain activity, and be synchronised with the changing visual pattern on the screen to detect any delay in responding. You don't have to do anything except stay alert and look at the screen. The test will be repeated for each eye in turn, and the whole process should take around 30-45 minutes. 

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Evoked potentials test in the diagnosis of MS

Professor Coles talks about what happens in a evoked potential tests, what different ones there are and how they work.

What do I need to do for an evoked potentials test?

Performance on an evoked potential test is affected by fatigue, so try to get plenty of rest before you go in for your test.

  • Wash your hair the night before, and don't use any hair products on it on the day of the test.
  • You will need to remove all jewellry, braids and hair clips for the test.
  • You can normally eat and take your regular medication before an evoked potentials test, but you may be asked to delay taking medications that make you drowsy or sleepy until after the test.
  • If you wear glasses, don't forget to take them along.

Find out more

Walsh P, et al.
The clinical role of evoked potentials.
Journal of Neurology, Neurosurgery and Psychiatry 2005;76 Suppl 2:ii16-22.
Full article (PDF, 257KB) (link is external)
Kraft, GH
Evoked Potentials in Multiple Sclerosis
Physical Medicine and Rehabilitation Clinics of North America Volume 24, Issue 4, November 2013, Pages 717-720
Summary (link is external)
Pokryszko-Dragan, A et al.
Assessment of visual and auditory evoked potentials in multiple sclerosis patients with and without fatigue
Neurol Sci. 2015; 36(2): 235–242.
Full article (link is external)
Schlaeger, R et al.
Combined visual and motor evoked potentials predict multiple sclerosis disability after 20 years
Multiple Sclerosis Journal 2014, Vol. 20(10) 1348–1354
Summary (link is external)
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