Evoked potentials
In MS, conduction in various nerves is slowed down, because the myelin sheaths which cover, insulate and protect the nerve fibres are damaged. In these areas of ”stripped” nerves, transmission of impulses is markedly delayed.
When measuring evoked potentials (EPs), the time it takes for a stimulus to reach the brain must be precisely recorded. Delays are detected by comparing the test results with the time it normally takes to transmit impulses in people without MS.
By measuring the brain’s electrical activity, neurologists may find lesions that do not cause clinical symptoms. Non-invasive techniques such as evoked potentials, which reveal the brain’s electrical response to certain stimuli, are still valuable, especially for someone for whom the diagnosis is in doubt.
Evoked potentials can help neurologists find abnormalities in nerve conduction and so-called “silent” lesions in the central nervous system, even when no neurological deficits have shown up so far.
Evoked potentials are not only useful for diagnosing MS they are also important indicators of the course of the condition.
Visual evoked potentials
Visual evoked potentials (VEPs) are most commonly performed in the framework of an MS diagnosis. The time it takes for the optic nerve to transmit visual information to the brain area primarily responsible for processing visual information is measured by capturing VEPs.
In preparation for this non-invasive test, electrodes are placed on your head which detect electrical activity (brain waves) within your brain. In order to measure the impulses travelling along the optic nerve between eyes and brain, you are asked to focus on a chessboard-like screen with a tiny square in the middle.
Damage to the optic nerve can cause an abnormal VEP. Therefore such a finding in a person with clinically normal vision may help support the diagnosis of MS, since abnormal VEPs are seen in 75–97% of MS patients.
