What is it like to have an evoked potentials test?

1 January 2022

A woman with MS shares her experiences of evoked potentials tests during her diagnosis.

Visual Evoked Potential (VEP) is a test of the speed of nerve messages between the eye and the brain. SomatoSensory Evoked Potentials (SSEP) tests the speed of nerve messages between the skin and the brain.

These tests are very similar and may be arranged at the same out-patient appointment. You will not need to stay in hospital overnight. You should get an appointment letter with information about what to expect and how long they expect the test to take.

There isn't any special preparation needed for these tests, so you can eat, drink and take medicines as normal, unless they say otherwise. For both these tests you will have to be in a room on your own. You will have a few electrodes put on your head with sticky jelly and or tape. It is quite useful to have a brush ready to help tidy up afterwards.

For Visual Evoked Potentials, the team will ask you to sit down and watch patterns on a screen. They cover one eye at a time, so that the eyes can be tested separately. It is necessary to concentrate and look at what they have asked you to look at, but doesn't really require you to do anything else.

If you wear glasses when watching a TV at home, bring these with you. If you use different glasses for distance and close work, then bring both sets, just in case.

For SomatoSensory Evoked Potentials you will need to have electrodes attached to an arm and/or leg, so it can be helpful to have the sort of clothing that allows easy access to your arms and legs. The tester will ask you to relax sitting or lying down.

This is actually not quite as easy as it sounds, since there can be a great temptation to react to everything strange happening. You get little jolts from tiny electric shocks as they test a nerve to see what response it produces. If the muscle does twitch, you have to let that happen and try not to react to it. Some the shocks can be rather odd, almost painful, but they are very short lived and do not do any harm.

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