Somatosensory Evoked Potential (SEP) Test: What it is for


Somatosensory evoked potential (SEP) tests are commonly used to detect problems during surgeries that might affect your brain, spinal cord, or nervous system. But that’s not all.

Evoked potential tests are used to examine the strength and speed of electrical activity in your body. They measure the electrical impulses that travel to and through your central nervous system in response to a stimulus.

Somatosensory evoked potential tests are sometimes abbreviated to “SEP” or “SSEP”. They are also called somatosensory evoked responses (SER or SSER) tests. All of these names and abbreviations refer to the same test.

Other types of evoked potential tests include:

Let’s take a closer look at how SEP tests work, why you need one, and what to expect.

Other evoked potential tests measure electrical activity between your eyes and your brain or your ears and your brain. What sets SEP tests apart is that they monitor electrical pathways from your limbs all the way to your brain.

Electrodes can be placed on arms, legs, or both. These electrodes provide very mild electrical stimulation. When the cells in your skin, muscles, and nerves sense this stimulation, they relay that information to your brain.

Another set of electrodes is attached to your scalp, spine, or both. These electrodes do not provide electrical stimulation. Instead, they measure the intensity — called amplitude — of the signal traveling from your nerves to your brain. They also measure whether there is a delay – called latency – in the signal.

SEP tests are most frequently Used during surgeries that may affect your brain, spinal cord, or nervous system. By measuring electrical activity during surgery, doctors can avoid damage that would otherwise only be visible after surgery.

SEP tests can also be used to diagnose neurological disorders such as multiple sclerosis (MS). In these cases, SEP testing is usually just one of many tests done to gather information and narrow down the possible causes of your symptoms.

SEP tests can be used to diagnose conditions affecting your nervous system. If you have symptoms such as uncoordinated movements, poor balance or muscle weaknessa SEP test is a tool that might help pinpoint the cause.

For example, tumors on or near your spine could affect your body’s ability to transmit signals from your limbs to your brain. In this case, a SEP test could help shed light on the location of the problem.

It is also common for some surgeries to run a SEP test at the same time. In these cases, you won’t be awake for the test, but you can notify the surgical team if your nervous system is adversely affected by the procedure.

Some operations that might involve a SEP test include:

Before your exam

Before taking a SEP test, be sure to ask your doctor how to prepare for it. In most cases, you won’t need to fast or stop medication, but that may not be the case for everyone.

If you have hair, you should wash it the night before the test so that the electrodes can be easily placed on your scalp. Avoid using hairspray, gel or other styling products.

during your exam

You will be asked to sit in a chair or lie down on a table. You may need to wear a hospital gown so doctors can access your arms, legs, and back.

A doctor places electrodes on your scalp and spine, as well as on your arms, legs, or joints. The electrodes are attached with an adhesive.

Electrodes on your limbs emit small electrical impulses. You may feel a little uncomfortable, but it shouldn’t be painful.

The test usually lasts between 1 and 2 hours.

After your exam

The SEP test provides instant results. The doctor may be able to give you the results right away. Sometimes your SEP test is one of many tests, so the results may not be meaningful until all tests are complete.

If the test was not performed by the referring doctor, the results will be sent to them. Your doctor will let you know the results after they have had a chance to review them.

SEP tests are considered very safe and do not pose any significant health risk. Be sure to speak with your doctor about any specific concerns you may have before your test.

The results of a SEP test show which pathways in your nervous system are functioning properly and which are dysfunctional. Your doctor can use this information to determine the cause of your symptoms.

A SEP test alone does not usually lead to a diagnosis, but it often helps rule out some conditions.

If you’re expecting a SEP test to be performed, you might have a few questions. Make sure to ask your doctor ahead of time how to prepare and what to expect from the results.

How long does a SEP test take?

If your SEP test is performed as part of a surgical procedure, it will likely last for the duration of the surgery. In this case, you will probably be unconscious the whole time.

If you complete a SEP test alone, you can expect it to take between 1 and 2 hours.

Why is a SEP test performed?

SEP tests are used during some surgeries to provide doctors with feedback on possible nerve damage throughout the procedure. This helps them avoid permanent damage.

You may also need a SEP test if your doctor is trying to diagnose or monitor the progression of a neurological condition. SEP testing can help pinpoint the source of problems with proprioception, or your sense of how your body is aligned in space.

Does a SEP test hurt?

No, SEP tests are not painful. The electrical impulses can cause tingling, which can cause mild discomfort. SEP tests rarely cause mild skin irritation.

SEP tests are used to measure how well your nervous system relays messages from your limbs to your brain. It can be used to diagnose neurological problems or conditions affecting your nervous system.

SEP tests are used during some surgeries so doctors don’t damage your nervous system if you are unable to describe how you are feeling.

It’s a safe and minimally invasive test, and results are usually available quickly.


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