When you have the tests, you’ll have wires placed on your scalp. It’s safe and painless. It usually takes about two hours to do all three types of evoked potential tests. A doctor with special training in these tests will interpret the results. While evoked potentials can help diagnose multiple sclerosis, they can’t let your doctor know for sure whether the condition is causing problems with the signals in your nerves or if they’re happening because of another health problem. Your doctor will consider the results of these tests along with those of other lab tests and your symptoms before making a diagnosis.