As your body experiences light, sound, touch, and other sensations, your brain assimilates that information as a series of electrical signals. If you have multiple sclerosis (MS), the disease causes nerve damage that can slow, distort, or stop this activity altogether. Evoked potential examinations can help physicians see if this is happening to you.
The tests measure electrical activity in parts of the brain caused by light, sound, and touch. They can help doctors diagnose a person with MS because they can detect problems along some nerves that are too subtle to detect by other tests.
There are three different types of PD tests that have been used to help diagnose MS.
Visual evoked potentials (PEV). This test detects vision loss from optic nerve damage. The patient is seated in front of a screen and focuses on the center, where a checkerboard pattern scrolls. One eye is examined at a time and each eye is examined twice.
Auditory Brainstem Evoked Potentials (BAEP). This test assesses high-frequency hearing loss, diagnoses auditory nerve damage, and can detect small tumors in the inner ear (acoustic neuroma). The patient is sitting in a room with headphones on. A series of clicks will be sent through the headphones, one at a time, to one ear. Each ear is tested twice.
Somatosensory evoked potentials (SEP). It measures how long it takes for peripheral nerves (nerves outside the brain and spinal cord) to respond to stimuli. It can detect nerve or spinal cord damage due to MS or other degenerative diseases. In this test, the patient receives electrical impulses in the arm or leg.
Current criteria for a diagnosis of MS consider only visual evoked potential tests because this test has been shown to be more useful. As mentioned earlier, the VEP test detects vision loss from optic nerve damage, which is a common early symptom in MS.
Although EF tests are used for the diagnosis of MS, they are not specific to this condition. Other tests should be considered before a diagnosis of MS can be made.
Uses
Physicians often use evoked potential exams to confirm a diagnosis or monitor the nervous system, rather than to determine the cause of a slow reaction.
MRIs and cerebrospinal fluid tests are the main ways to diagnose MS today.
However, an evoked potentials test can still complement or confirm an MS diagnosis. It can be a valuable tool to demonstrate slow signal transmission.
A study that researchers published in 2016 notes that a test of evoked potential:
- is an inexpensive method of diagnosis
- can supplement the results of other tests
- it is the only way to assess how well myelin, axons, and synapses are working in specific sensorimotor pathways
In addition to playing a role in the diagnosis of MS, an evoked potentials test can:
- evaluate hearing or vision
- detect lesions and tumors
- detect damage to nerves, such as the optic nerve
- assess brain activity in coma patients
- diagnose and monitor diseases that damage the nerves
Risks
Evoked potential testing is a low-intensity procedure and generally presents little risk to the person beyond a slight discomfort during the test.
The test may be less effective in a individual with advanced symptoms. Muscle spasms or severe visual or hearing impairments can affect the accuracy of the test.
How do I prepare for an Evoked Potential (EP) Testing?
Here is a list of common steps that may be required of you:
You will sign a consent form that gives you permission to perform the procedure. Recite the form carefully and ask queries if something is not clear.
Generally, no prior preparation is required, such as fasting or sedation.
Tell your healthcare provider about all medications (prescription and over-the-counter) and herbal supplements that you are taking. He or she will let you know if you can take your medications before the test.
Wash your hair the night before the test, but do not use conditioner or apply hairspray or other hair products.
Depending on your medical condition, your healthcare provider may request other specific preparations.
What should I except
Generally, the evoked potentials test follows this process:
You will be asked to remove clothing, jewelry, hairpins, glasses, hearing aids, or other metal objects that may interfere with the procedure.
If you are asked to remove your clothing, you will be given a gown to wear.
You will be asked to relax in a reclining chair or lie down on a bed.
A paste will be used to join the electrodes. The electrodes will be placed according to the type of evoked potential test being performed.
The test will generally proceed as follows:
Visual evoked potential (VEP)
You will be sitting a few feet from a screen.
Electrodes will be located on your scalp over the parts of the brain responsible for interpreting visual stimuli.
You will be requested to focus your look on the center of the screen.
Then you will be asked to close one eye at a time while the screen displays a checkerboard pattern. The squares on the chessboard change color once or twice a second.
Auditory Brainstem Evoked Response (BAER)
You will sit in a soundproof room with headphones.
Electrodes will be placed on the top of the head and on one earlobe and then the other.
A click or other auditory stimulus will be sent through the headphones to the ear under test, while a “masking” noise will be sent to the other ear to protect it from the stimulus.
Somatosensory evoked potential (SSEP)
Electrodes will be placed on your scalp and in one or more places on your body, such as your wrist, the back of the knee, or your lower back.
Small, painless electrical shocks will be delivered through electrodes placed on the body.
For each of the tests, the electrical activity detected by the electrodes on the scalp will be fed to a recorder, which amplifies the signal and graphs so that your doctor can interpret the results.
Once the test is whole, the electrodes will be detached and the electrode paste will be washed off. In some cases, you may need to wash your hair again at home.
Your healthcare provider will let you know when to resume any medications you stopped taking prior to the test.
The day of the test
Your child will come to the Department of Clinical Neurophysiology which is located on Level 4, Southwood Building.
Once you are in the Department, check in at reception and soon there will be a Clinical Physiologist (CP) who will confirm your data and that of your child and take you to the recording room. They will explain in more detail how the test will be conducted, discussing any concerns you may have.
Depending on the information the doctor needs, your child may have all three types of PE tests or just one or two. This will be fully explained before the test begins.
What does the test involves?
The CP will place small silver discs (electrodes) at certain points on your child’s scalp and face using a soft paste. Sometimes they will measure your child’s head beforehand and mark the spots with a soft pencil before placing the electrodes. Additional electrodes may be applied to the neck, shoulders, lower back, and / or legs if your child is doing an SSEP.
As each electrode is placed, the CP will clean the scalp area with a cotton swab and a little cream. This doesn’t hurt, but some kids don’t like it. While all the electrodes are in place, your child can sit on a chair, bed, or lap, and can play with toys; We have many toys in the department, but feel free to bring your child’s favorite book, toy, or quilt.
Visual evoked potential (VEP)
For this test, your child will need to look at a flashing light. Sometimes a television screen can be used that shows a checkerboard pattern moving from side to side. As the light flickers or the pattern moves on the TV screen, the brain responds to the stimulation and this is recorded as brain waves.
Auditory Brainstem Evoked Potential (BAEP)
For this, we will place hearing aids over your child’s ears; if your child is not used to wearing hearing aids, you can prepare for the test with games as described in another information sheet available on our website at www.gosh.nhs.uk/ conditions-and-treatments / procedures-and-treatments / help-your-child-to-use-hearing-aids-hearing-assessment We stimulate one ear at a time by playing a clicking sound. As this happens, the brain responds to the stimulation and this is recorded as brain waves.
Somatosensory evoked potential (SSEP)
In addition to the electrodes on the head, your child will have one or two electrodes attached to her wrist and / or ankle that allow her to apply a small electrical pulse to her skin; This will make your fingers or toes tingle and move, but it doesn’t hurt.
For all three EPs, we repeat each stimulus several times so that many responses are recorded and averaged to show how the nerve pathways work. The brain’s response to this stimulation is recorded as brain waves.
What happens during an evoked potential test?
Brainstem Auditory Evoked Answer (BAER): The BAER helps measure the auditory nerve pathways from the ears to the brainstem. Electrodes are placed on the scalp and earlobes, and headphones are placed over the ears. The headphones emit a series of clicks or tones to each ear separately.
Visual Evoked Response (SEE): SEE assesses the visual nervous system from the eyes to the occipital (visual) cortex of the brain. Electrodes are applied to the scalp. Typically, patients are asked to watch a pattern on a video screen while remaining fully alert. Each eye is tested separately. After the test, a technician will remove the electrodes and adhesive from your scalp. However, you may want to wash your hair thoroughly when you get home. Your diet and doings should not be pretentious by the test.
The results of the EP test will be interpreted by one of our neurologists and a report will be sent to your doctor or discussed with you at your next neurology appointment.
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