This description is the personal experiences of a woman with MS who underwent an evoked potentials tests during her diagnosis
Visual Evoked Responses (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 out-patient tests are very similar and may be arranged at the same appointment. The appointment letter should come with some information about what to expect and how long they expect the test to take. There isn't any special preparation needed, 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 (quiet) 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
Visual Evoked Potentials
For Visual Evoked Potentials, they 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 (it may be worthwhile to bring all your glasses, if you use different ones for distance and close work).
SomatoSensory Evoked Potentials
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.
This page will be reviewed within three years