A motor evoked potential (MEP) test can determine whether there is any damage along the nerves in the brain and spinal cord. It is a painless procedure but may cause some skin discomfort.

An MEP test is one type of evoked potential test that evaluates the function of pathways that control movement.

The test may also help monitor disease progression in people with multiple sclerosis (MS).

Read on to learn what MEP tests are, why doctors may recommend them, and what research says about this type of test.

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Evoked potential tests are exams that study the signals that the brain and spinal cord receive from other areas of the body. These tests also check vision, hearing, and sensory function.

In addition to a motor evoked potential test, other types of evoked potential tests include:

  • visual evoked potential test
  • brain stem auditory evoked potential test
  • somatosensory evoked potential test

Learn more about evoked potential tests here.

Doctors use MEP tests to examine the motor pathways when a person undergoes brain, spinal, or aortic surgery. This can help prevent damage to these pathways, since motor dysfunction may occur after surgery.

MEP tests may also be beneficial in intraoperative neurophysiological monitoring (IONM) to help prevent spinal damage. IONM aims to protect the nervous system and avoid paralysis or loss of sensation.

MEP tests can also help determine whether a person has early stage neuronal ischemia. This can happen after a stroke when the brain neurons do not get enough nutrients.

Doctors record MEP tests by attaching electrodes to a person’s scalp and muscles to measure the muscles’ responses to stimulation.

On the day of the evoked potential test, people should avoid wearing jewelry, hair clips, and other accessories. People may also want to avoid hairstyling products. These can affect the readings too.

Fasting may not be necessary, but the doctor ordering the test may recommend not taking medications that can cause drowsiness before the procedure.

Typically, the test is an outpatient procedure. People do not have to stay overnight for monitoring.

During the evoked potential exam, people may have to remove their clothing and wear a gown.

The doctor will use a soft paste to attach the electrodes to the skin and take electrical activity readings. Sometimes they will insert very small needles into different muscles of the body.

Research into MEP tests suggests they are affordable, can help with diagnosis, and can reduce the risk of postsurgical complications in some cases.

A 2017 research review notes that evoked tests are inexpensive, and doctors can use them as a form of diagnostic test.

A 2021 study suggests that MEP testing can help reduce a person’s chances of developing neurological complications during spinal cord tumor resection surgery, such as postsurgical motor issues.

A 2018 retrospective study suggests that medical professionals may use MEP tests for children up to 15 years old undergoing brain tumor surgery.

However, researchers found it was more challenging to get readings from participants under the age of 5 because they had a low transcortical response compared with children aged 6–15 years. This may be because their central nervous system is relatively immature.

Issues getting readings can also happen in adults. For example, people with blood flow disturbances may show signal deterioration in their MEP test results. This can happen in people with low blood pressure or people who develop neuronal ischemia from a stroke.

After a stroke, some people may experience aphasia. This disorder affects a person’s ability to communicate clearly. According to a 2018 longitudinal study, MEP tests of the upper limbs may help determine aphasia severity within 15 days of a stroke.

MEP tests may be beneficial for monitoring people with MS. These tests can also help prevent complications in people who undergo spinal or brain surgery.

An MEP test is a painless procedure. It may also be safe for children.

On the day of the procedure, it is best to avoid wearing jewelry or applying hairstyling products, as these may interfere with the test results.