A somatosensory evoked potential (SEP) test examines how the spinal cord and brain transmit information. It can detect spinal cord problems that may cause arm and leg numbness.
A SEP test is one of the three sensory evoked potential exams that measures electrical activity in the brain that results from sight, sound, or touch. SEP tests focus on electrical activity in the brain resulting from touch.
The test is noninvasive, and doctors commonly use it, even though imaging tests, such as MRIs, are available.
In this article, we examine SEP tests in more detail. We look at how they work and why doctors use them. We also discuss the procedure, possible risks and complications, and what the results could mean.
A medical professional attaches electrodes to an individual’s back, wrist, and scalp and sends a mild electrical stimulus. The scalp’s electrodes measure the time it takes for the electrical current to travel to the brain.
SEP tests are painless, but people may experience muscle tingling or twitching. The test typically takes up to 2 hours.
Healthcare professionals can recommend SEP tests to individuals of any age group.
The American Association of Neuromuscular & Electrodiagnostic Medicine mentions other uses of SEPs, such as:
A person may undergo a SEP test if they have muscle weakness or doctors suspect they have MS.
Symptoms of MS may include:
People may need to sign a consent form before their SEP appointment.
People should inform a doctor of any medications they usually take, including supplements. There is no need to fast for a SEP, and doctors perform it without sedation.
Before the test, people should not apply hairspray, mousse, gel, or oil to their hair or use skin moisturizers, as they may interfere with the test results. They should also wear loose-fitting trousers and a top to access the points doctors need to place the electrodes easily.
Doctors will discuss with individuals what they should expect on the day. The procedure may occur on an outpatient basis or as part of a hospital stay.
Generally, people have to remove jewelry, glasses, hearing aids, and hairpins, which can interfere with the test. They may also wear a hospital gown.
The following steps may occur during a SEP procedure:
- The doctor uses a soft paste to help attach the electrodes or silver discs to the scalp, back, and shoulders.
- They send electrical shocks through the electrodes on the body. However, these should not cause any pain.
- The medical team uses a recorder that detects the electrical activity and transfers it to a chart for result interpretation.
Some factors or health problems can interfere with a sensory evoked potential test result. These include:
Additionally, SEPs may be
A SEP test may provide the following results:
- Typical: The time between the stimulation and nerve response may be as healthcare professionals usually expect.
- Atypical: Atypical results may be possible if a person does not have any symptoms in their nerve area. However, this may mean they have a neurological-related disorder.
After the SEP test, a healthcare professional removes the electrodes. A person’s hair may feel sticky until they wash it.
People undergoing the SEP procedure should ask a healthcare professional who they can contact if they have any questions or problems.
A healthcare professional may suggest when to resume medications the individual stopped taking before the appointment. They may also discuss how and when they receive the results.
Below are answers to three common questions about SEP tests.
How long do they take?
The duration of a SEP depends on the individual’s symptoms and the doctor carrying out the procedure. However, the exam should not take longer than 2 hours.
What do SEPs feel like?
While SEP procedures should not cause any pain, skin irritation may develop on rare occasions.
Are SEPs safe for children?
SEPs are safe for children. The test can sometimes be slightly uncomfortable, but it should be painless. Sometimes, skin irritation from the electrodes may develop temporarily.
SEP tests are beneficial in examining how the spinal cord and brain transmit information. Doctors may recommend them if a person has muscle weakness.
The procedure can take up to 2 hours and is safe for adults and children.
Minor irritation may occur from contact between the electrodes and the skin, but this is rare.