Evoked Potentials

This leaflet is for patients who have been informed that they need evoked potentials tests during their outpatient visit.

This is carried out in the Neurophysiology department. Neurophysiology is the study of brain, spinal cord nerve and muscle function.

These tests record and interpret electrical signals from the body to help diagnose disorders.

What are Evoked Potentials?

Evoked potentials are signals produced in your brain in response to external stimuli. This test checks how the signals reach your brain from your nerves.

What do I need to do to prepare for the test?

• Before you come for the test you can have your meals at normal times and continue taking any current medication you are on unless you have been advised otherwise by your clinician.
• Bring a list of your medication and any allergies with you to the appointment.
• Wear loose fitting clothing so that your legs, back, arms and shoulders can easily be reached. The clinician may ask you to remove some jewellery as it might interfere with the test.

Important: On the morning of your test please do not use body creams/lotions on your arms and legs as this may affect the test and results.

What will happen during my test?

The test will be carried out by a doctor or an expert in evoked potentials, a Clinical Physiologist.

• You will be asked a few questions and given an explanation of the procedure. If you have any questions about the test, please do not hesitate to ask.
• The clinician will start by measuring your head and drawing some little dots with a marker on the surface of your head. The clinician will gently rub the marks with some gel, before attaching 23 small discs to the surface of your head using a sticky paste. This is not painful.
• If you are having somatosensory evoked potentials, a small electrical stimulator will be used to apply electrical stimulus to your nerves. This will cause a strange tingling or tapping sensation and some twitching of the muscles in your hand or foot.
• If you are having visually evoked potentials, you will be asked to look at a screen with a checkerboard pattern.
• Most patients do not find these tests painful.
• You can bring someone with you to your appointment if you wish.

What will happen after my test?

Once the test is complete, the discs will be removed and you can return to your normal activities. There should be no after effects of the test.

Small pieces of sticky paste may be left in your hair which easily washes out with shampoo and warm water.

The results of the tests will take a few weeks to be analysed by the physiologist and consultant. You hospital clinician will contact you if something of concern is detected by the test, otherwise your hospital clinician or referring doctor will discuss the results with you at the next appointment.

Your GP will receive a copy of the results and you may ask the GP for a copy, if you wish.

Contacts

Neurology (Neurophysiology Department)

020 8934 6156 (Option 3)