Evoked potential (EP) tests measure the electrical activity of the brain in response to stimulation of specific sensory nerve pathways. They can detect the slowing of electrical conduction caused by damage (demyelination) along these pathways even when the change is too subtle to be noticed by the person or to show up on neurologic examination. Because the diagnosis of MS requires evidence of demyelination in two distinct areas of the central nervous system, EP testing was previously used to help confirm the diagnosis by enabling the physician to identify a second demyelinating event that caused no clinical symptoms or was not otherwise apparent.
Other conditions can produce abnormal EP results as well. Magnetic Resonance Imaging (MRI) and Cerebrospinal Fluid (CSF) show findings that have been found to be more specific to MS and are now the only two types of tests used to confirm the diagnosis of MS. EP testing has been eliminated from the 2017 Revised McDonald Criteria for the Diagnosis MS.