Evoked Potentials for Diagnosing Multiple Sclerosis

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Evoked potential tests measure how long it takes for stimulation of different nerves to reach the brain and how big the response is. The speed of the impulses along nerve pathways can indicate if there has been damage (like demyelination caused by MS) to the nerves, as the impulses will travel more slowly to the brain.

Three Types of Evoked Potential Testing

There are three evoked potential tests used in evaluating MS:

  • visual evoked potentials (VEPs)
  • somatosensory evoked potentials (SSEP)
  • brainstem auditory evoked potentials (BAEP)

For all of the tests, electrodes are applied to the scalp with conducting gel. They are placed in different locations on the head according to which type of evoked potential they are recording. A neurophysiologist interprets the findings of the test, determining whether the brain's electrical activity is slowed from the nerve damage of MS.

Visual evoked potential testing can be particularly helpful in confirming a diagnosis of MS. VEPs can reveal any nerve damage along the optic nerve pathways, which is a common finding in MS, even if a person has never had any vision changes or symptoms. This testing is done by measuring the brain's response to light. The eyes are stimulated by looking at a computer screen that is flashing checkerboard patterns of differing sizes or a strobe-type light. Usually, one eye is covered with a patch or a hand-held shield while the other eye is tested, then the process is repeated with the other eye. Some people report feeling slightly nauseated during the test, a feeling much like mild motion sickness.

SSEP measures the brain's response to sensation. The nerves of the arms and legs are stimulated by an electrical pulse delivered through electrodes stuck onto the skin, usually at the wrist or knee, but occasionally near an ankle or elbow. It feels like a small electric shock. Most people say this is completely painless, but some people find the stimulation bothersome.

BAEP measures the brain's response to sound, by delivering clicks, tones, or beeps to a person's ear using headphones.

Using Evoked Potentials to Confirm a Diagnosis of Multiple Sclerosis

Evoked potential tests may be used when MS is suspected, but a neurological examination alone does not provide enough evidence. They are becoming less popular with the widespread availability of MRI scans. But evoked potentials are still used in some cases, especially if symptoms indicate that there might be damage to places that are hard to capture on an MRI scan, like the optic nerve.

In addition, besides better understanding the presence or degree of MS-related nerve damage, evoked potentials may serve other roles, like serving as a marker of fatigue or disease progression in MS patients. 

Bottom Line

It's important to understand that evoked potentials are not required to make a diagnosis of MS nor are they ever used alone to make an MS diagnosis. Instead, they are tools that can help better understand or confirm a person's MS diagnosis and may have future roles in MS, as recent research suggests.

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Article Sources
  • Birnbaum, M.D. George. (2013). Multiple Sclerosis: Clinician’s Guide to Diagnosis and Treatment, 2nd Edition. New York, New York. Oxford University Press.
  • National MS Society. Evoked Potentials. 

  • Pokryszko-Dragan, A., Bilinska, M., Gruszka, E., Kusinska, E., Podernski, R. Assessment of visual and auditory evoked potentials in multiple sclerosis patients with and without fatigue. Journal of the Neurological Sciences, Feb;36(2):235-42. doi: 10.1007/s10072-014-1953-8.