Evoked potential test and results
Evoked potential tests measure the time it takes for the brain to respond to sensory stimulation either through sight, sound, or touch.
Doctors use the test to help diagnose multiple sclerosis (MS) and other conditions that can cause a person’s reactions to slow. The test can detect unusual responses to stimulation.
The popularity of the evoked potential test has fallen in recent years, as MRI scans have a good record of accurately showing lesions that occur in multiple sclerosis.
What are the evoked potential tests?
The nervous system connects the body through a series of cells that communicate with electrical signals.
When the body receives a stimulation, electrical signals go to the brain through the nervous system.
The stimulation can be:
- Visual, entering the body through the eyes
- Auditory, entering through the ears
- Somatosensory stimulation or touch, when sensations enter via the skin
For example, when light bounces off an object, it stimulates the eye’s sensory receptors, receptors send electrical signals to the brain.
The stimulating signal of light reaches the brain more slowly than the tactile stimulus. This is because when a person sees something, the body must first convert the light into an electrical signal before sending it to the brain.
A defect in the immune system damages the fatty layer of myelin that protects nerve cells. This loss affects the speed at which electrical signals can travel through nerve cells.
Evoked potential tests measure the time it takes for the brain to respond to sensory stimuli as a way of detecting and monitoring problems or irregularities with how the nervous system is functioning.
Uses of evoked potential test
Doctors often use evoked potential tests to confirm a diagnosis or monitor the nervous system, rather than to determine the cause of a slow reaction.
MRI scans and tests of cerebrospinal fluid are the main ways of diagnosing MS nowadays.
However, an evoked potential test can still supplement or confirm a diagnosis of MS. It can be a valuable tool for demonstrating a slow signal transmission.
A study that researchers published in 2016 notes that an evoked potential test:
- An economical method of diagnosis.
- Complement results of other tests.
As well as playing a role in the diagnosis of MS, an evoked potential test can:
- Assess hearing or sight
- Detect lesions and tumours
- Detect nerve damage, such as to the optic nerve
- Assess brain activity in coma patients
- Diagnose and monitor diseases that damage nerves
What to expect
The doctor advises the person what to do and what to expect before the test.
The individual will need to:
- Sign the consent form
- Tell your doctor about health problems, allergies, and medications you are using.
- Bring your glasses if you are doing a visual inspection.
They do not require fasting or medication before the test.
Types of test
In an evoked potential test, the person will sit in a chair, and a healthcare provider will place electrodes on the relevant part of the body. The electrodes will record electrical signals that travel to the brain.
There are three main types of test.
Visual evoked response test
The healthcare provider will place electrodes on the scalp.
The person will sit and focus on the centre of a screen a few feet away. They will need to close one eye at a time and gaze at a checkerboard pattern on the screen. The colours of the squares will alternate once or twice each second.
The test will record how the eye responds to the changing patterns.
Brainstem auditory evoked response test
The person will sit in a soundproof room, wearing earphones. The electrodes will be on the top of the head and first one earlobe, then the other.
The person will hear clicking sounds or tones in one ear, while a masking sound prevents the other ear from picking up the signal. Then the other ear will be tested.
The time it takes to respond to the signal can show whether there is damage to the auditory pathway within the brain or the acoustic nerve connecting the ear to the brain.
Somatosensory evoked response test
The individual will sit or lie in a comfortable position.
The health professional will place electrodes on the scalp and relevant areas of the body, such as the arm, leg, or lower back.
They will then deliver a low-intensity electric shock through the electrodes and record the time it takes for the brain to respond to the signal. The shock should not be painful, but it may be uncomfortable for a short while.
The professional will apply the stimulus to the part of the nervous system where damage might be present, for example, the spinal cord.
If the results show an unusually long signal transmission time, this could indicate damage to a nerve pathway, even in “silent” cases when a person is not experiencing symptoms.
A doctor will usually use an evoked potential test alongside an imaging test to investigate the problem in more detail. This may be an MRI or CT scan.
Evoked potential test risk factors
Evoked potential tests are a low-intensity procedure and, typically, pose little risk to the person beyond minor discomfort during the test.
The test may be less effective in a person with advanced symptoms. Muscle spasms or severe visual or hearing impairments might affect the accuracy of the test.
Evoked potential test results
If the test indicates that multiple sclerosis (MS) might be present, a doctor will usually do further tests to confirm the diagnosis and rule out other possible causes of symptoms.
If the results of all the tests indicate MS, a doctor will work with the individual to provide appropriate treatment and monitoring.
In the past, doctors considered Multiple Sclerosis (MS) untreatable, but scientists are making rapid progress in understanding MS and developing new treatments.
A type of medication known as a disease-modifying therapy (DMT) can reduce the number of flares in a kind of MS doctors call remitting relapsing MS (RRMS). When a person has RRMS, symptoms can temporarily worsen and then get better again.
DMT may also slow the progression of MS and reduce the risk of more severe symptoms appearing in time. For people who experience severe symptoms, various treatment options are available to help them manage their condition.