Evoked Potentials

What are evoked potentials? 

Evoked potentials (EPs) are neurological tests that measure the brain’s electrical responses to sensory stimuli, such as visual patterns, sounds, or small electrical pulses applied to the skin. These responses help assess how well signals travel through the nervous system, which allows neurologists to detect abnormalities that may indicate nerve damage or neurological disorders. 

By analysing the timing and strength of these responses, evoked potentials can provide critical insights into conditions such as multiple sclerosis, optic neuritis, spinal cord injuries, and auditory or peripheral nerve dysfunction.

There are three main types of evoked potentials, each designed to evaluate a specific sensory pathway:

• Visual Evoked Potentials (VEP) — VEP assesses the function of the optic nerve and visual pathways in the brain. This test involves showing the patient a checkerboard pattern or flashing lights while electrodes on the scalp record the brain’s response. Delays in these signals may indicate optic nerve damage, often seen in conditions such as optic neuritis or multiple sclerosis. VEP is commonly used to investigate unexplained vision disturbances and monitor progressive neurological conditions.

• Brainstem Auditory Evoked Potentials (BAEP) — also known as Brainstem Auditory Evoked Responses (BAER), evaluate the auditory nerve and brainstem pathways. During this test, patients wear headphones that play a series of clicking sounds or tones while electrodes measure the brain’s response. Abnormal results can indicate hearing impairments, nerve damage, or disorders affecting the brainstem, such as acoustic neuromas or multiple sclerosis.

• Somatosensory Evoked Potentials (SSEP) — SSEP measures the function of sensory pathways from the peripheral nerves, through the spinal cord, to the brain. Small electrical pulses are applied to nerves in the arms or legs, and the brain’s response is recorded. Delays or weak responses can suggest spinal cord injury, nerve compression, or demyelinating diseases. This test is also used during spinal surgeries to monitor nerve function and prevent damage.

How do evoked potentials work? 

Evoked potential testing is a non-invasive procedure that records the brain’s electrical activity in response to sensory stimulation. The process begins with the placement of small electrodes on the scalp and, in some cases, other areas of the body, depending on the type of test being performed. These electrodes detect and record the brain’s response to specific stimuli, which can include visual patterns, auditory sounds, or mild electrical pulses applied to the skin. The recorded signals are then analysed to assess how efficiently and accurately sensory information is transmitted through the nervous system.

Each type of evoked potential test follows a specific process tailored to the sensory pathway being examined. 

• In a visual evoked potential (VEP) test, the patient is asked to focus on a screen displaying a changing checkerboard pattern or flashing lights, stimulating the optic nerve and visual pathways. 

• Brainstem auditory evoked potentials (BAEP) involve the patient wearing headphones while listening to a series of clicking sounds or tones, which helps assess the auditory nerve and brainstem function. 

• For somatosensory evoked potentials (SSEP), small electrical pulses are applied to the skin over peripheral nerves, typically in the arms or legs, to evaluate the conduction of sensory signals through the spinal cord to the brain.

During the test, the recorded signals are compared against standard response times to determine if there are any delays or abnormalities in neural transmission. Since evoked potentials measure nerve conduction speed and efficiency, they can detect disruptions in sensory pathways even before symptoms become apparent. 

The procedure is painless, requires no anaesthesia, and typically lasts between 30 minutes to two hours, depending on the specific test. Results are analysed by a neurologist, who interprets the findings to aid in diagnosing or monitoring neurological conditions affecting sensory function.

What are the benefits of evoked potentials? 

Evoked potential tests provide a reliable, non-invasive method for assessing nerve function and identifying abnormalities in sensory pathways. These tests play a crucial role in diagnosing neurological disorders, monitoring disease progression, and guiding treatment decisions.

• Early detection of neurological disorders — evoked potentials can reveal nerve dysfunction before symptoms become apparent; therefore, they aid in the early diagnosis of conditions such as multiple sclerosis, optic neuritis, and spinal cord disorders.

• Objective assessment of sensory pathways — unlike subjective tests that rely on patient responses, evoked potentials provide measurable data on how well sensory signals travel through the nervous system.

• Monitoring disease progression — for chronic conditions like multiple sclerosis, these tests help track changes in nerve function over time, which allows neurologists to assess treatment effectiveness.

• Surgical and intraoperative monitoring — somatosensory evoked potentials are used during spinal and brain surgeries to monitor nerve function in real-time, which reduces the risk of permanent nerve damage.

• Evaluation of unexplained sensory symptoms — patients experiencing vision disturbances, hearing loss, numbness, or tingling can undergo evoked potential testing to determine whether nerve dysfunction is contributing to their symptoms.

• Non-invasive and painless procedure — the test involves only surface electrodes and does not require injections, anaesthesia, or invasive techniques, which makes it safe and well-tolerated.

What conditions can evoked potentials help diagnose? 

At Siow Neurology, we use evoked potential testing to assess nerve function and identify disruptions in sensory pathways that may not be immediately apparent through standard neurological exams. These tests allow us to detect conditions early, track disease progression, and provide personalised treatment plans based on precise diagnostic insights.

• Multiple sclerosis — one of the most common uses of evoked potentials is in detecting nerve damage caused by multiple sclerosis. Delayed or abnormal responses in visual, auditory, or sensory pathways can indicate demyelination, even before symptoms fully develop.

• Optic neuritis — visual evoked potentials help assess inflammation of the optic nerve, which can cause sudden vision loss, blurriness, or pain with eye movement. This test is crucial for early detection and monitoring of optic nerve health.

• Spinal cord injuries — somatosensory evoked potentials are used to evaluate nerve conduction through the spinal cord, which helps assess the severity of spinal cord damage and monitor recovery over time.

• Acoustic neuromas and hearing disorders — brainstem auditory evoked potentials help detect tumours affecting the auditory nerve, as well as other conditions that impact hearing and balance.

• Peripheral neuropathies — evoked potentials can reveal abnormalities in nerve conduction that suggest conditions affecting peripheral nerves, such as diabetic neuropathy or Guillain-Barré syndrome.

• Demyelinating diseases — aside from multiple sclerosis, other conditions that damage the protective myelin sheath around nerves can be detected through evoked potential testing. 

• Unexplained sensory disturbances — for patients experiencing numbness, tingling, hearing loss, or visual disruptions without a clear cause, evoked potential tests help determine whether nerve dysfunction is involved.

What results can I expect? 

From the moment you arrive at Siow Neurology for your evoked potential assessment, our team ensures a smooth and comfortable experience. After discussing your symptoms and medical history, a neurologist or trained technician will explain the procedure and place small electrodes on your scalp and, depending on the test, other key areas such as your ears, wrists, or ankles. These electrodes record your brain’s response to specific sensory stimuli, such as visual patterns, clicking sounds, or mild electrical pulses applied to the skin. The entire process is non-invasive and painless, typically lasting between 30 minutes to two hours, depending on the type of test.

Once the procedure is complete, you can resume your normal activities immediately, as there are no side effects or recovery time required. Our specialists will then analyse the recorded signals and assess how quickly and effectively nerve impulses travel from the stimulated area to the brain. In a healthy nervous system, these responses occur within a predictable timeframe. Any delays or abnormalities in signal transmission may indicate nerve damage, demyelination, or other neurological conditions affecting sensory pathways.

The results of your evoked potential test will be reviewed in detail by your neurologist, who will discuss the findings with you during a follow-up consultation. If abnormalities are detected, further tests such as MRI or blood work may be recommended to pinpoint the underlying cause. For patients already diagnosed with conditions like multiple sclerosis or neuropathies, these tests help track disease progression and guide treatment adjustments. 

How many sessions are needed for evoked potentials? 

Evoked potential testing is typically completed in a single session. Most patients require only one appointment, during which the necessary tests are conducted based on the symptoms being evaluated. Depending on the condition being assessed, you may undergo one or multiple types of evoked potential tests; Visual Evoked Potentials (VEP), Brainstem Auditory Evoked Potentials (BAEP), or Somatosensory Evoked Potentials (SSEP), all of which can usually be performed within the same visit.

Each test generally takes 30 minutes to two hours, depending on the complexity and the number of tests needed. If ongoing monitoring is required for conditions like multiple sclerosis, your neurologist may recommend follow-up testing at specific intervals to track disease progression and treatment effectiveness. However, for most diagnostic purposes, one session is sufficient to gather the necessary information.

During your consultation at Siow Neurology, our specialists will determine the appropriate tests based on your symptoms and discuss whether any follow-up assessments may be necessary for long-term monitoring.

If you are experiencing unexplained vision changes, hearing difficulties, numbness, or other sensory disturbances, schedule a consultation with us for a comprehensive evoked potential assessment.

Frequently Asked Questions (FAQs) 

Is an evoked potential test the same as an EEG?

No, an evoked potential test measures the brain’s electrical response to specific stimuli, while an electroencephalogram (EEG) records the brain’s spontaneous electrical activity. 

How should I prepare for an evoked potential test?

Generally, you should wash your hair the night before the test and avoid conditioners or hair products, as they can interfere with electrode placement. Continue taking your usual medications unless advised otherwise by your healthcare provider. 

Are there any risks or side effects associated with evoked potential tests?

Evoked potential tests are very safe and typically have minimal or no side effects. A small number of patients may experience minor skin irritation from the electrodes. 

Can I eat or take my medications before the test?

Yes, in most cases, you can eat normally and continue taking your prescribed medications before the test. However, always follow any specific instructions provided by your healthcare provider. 

When will I receive the results of my evoked potential test?

The results are typically analysed after the test and sent to the clinician who requested it. They will discuss the findings with you during a follow-up appointment. 

Is sedation required during an evoked potential test?

Sedation is generally not needed for evoked potential tests, as they are non-invasive and painless. However, children or individuals who have difficulty remaining still may require sedation to ensure accurate results. 

What should I wear to the appointment?

It’s advisable to wear loose-fitting clothing so that areas like your arms, legs, and shoulders can be easily accessed during the test. You may also be asked to remove any jewellery that could interfere with the procedure. 

Are evoked potential tests used during surgeries?

Yes, somatosensory evoked potentials are often used intraoperatively to monitor the functional integrity of neural pathways, which helps prevent nerve damage during surgical procedures.