Multiple Sclerosis: Evoked Potential Tests

Evoked potential tests measure electrical activity in certain areas of the brain in response to stimulation of certain groups of nerves. These tests are often used to assist in the diagnosis of MS because they can indicate problems along the pathways of certain nerves that are too subtle to be noticed or found on a doctor's exam. Problems along the nerve pathways are a direct result of the disease. The demyelination causes the nerve impulses to be slowed, garbled, or halted altogether.

There are three main types of evoked potential tests:

• Visual Evoked Potentials (VEP): You sit in front of a screen on which an alternating checkerboard pattern is displayed.
• Brainstem Auditory Evoked Potentials (BAEP): You hear a series of clicks in each ear.
• Sensory Evoked Potentials (SEP): Short electrical impulses are administered to an arm or leg.

A fourth type of test -- motor evoked potentials -- can detect lesions along motor pathways (those that produce movement) of the central nervous system. This test is not commonly used to diagnose MS.

While evoked potentials are used to help diagnose MS, other conditions can also produce abnormal test results, so the tests are not specific for MS. To accurately diagnose MS, the information the tests provide needs to be considered along with other laboratory and clinical information.

How Are the Tests Performed?

Evoked potentials are recorded by placing wires with stimulators on the scalp over the areas of the brain.

How Long Do the Tests Take?

It usually takes about two hours to do all three types of evoked potentials.

A neurologist or neurophysiologist with special training in these tests will interpret the results.

Is the Test Safe?

Evoked potential testing is harmless and painless.

Reviewed by the doctors at the Mellen Center for Multiple Sclerosis Research at The Cleveland Clinic.