Electrodiagnostic (EDX) tests are diagnostic testing tools used to assess the health of muscles and the nerves that control them. These tests can help reveal diseases that cause muscle or nerve dysfunction and may be performed alongside a nerve conduction study. Electrodiagnostic testing has two forms: nerve conduction studies (NCV), also known as a nerve conduction velocity (NCV) test, and electromyography (EMG).
The guide below will provide information on an EDX test, including how to prepare for it and what conditions it can help diagnose.
What is an Electromyography Test?
An electromyography (EMG) is a medical test that helps doctors diagnose various conditions affecting muscles and nerves.
Every movement, from walking across the room to lifting your arms, involves communication between your brain, nerves, and muscles. To move, the brain sends signals to your nerves that travel through the spinal cord and then to the muscles. These signals involve electrical stimulation, which causes your muscles to contract.
An EMG test measures muscle response and evaluates the function and condition of your muscles.
A breakdown can occur at any point during this complex message system, affecting muscle movement. Several different diseases and injuries may affect this messaging system.
What Is A Nerve Conduction Study?
Depending on the situation and symptoms, a provider may perform an NCS alongside an EMG test.
A nerve conduction study (NCS) is a diagnostic test that assesses the health and function of your peripheral nerves located outside the brain and spinal cord. These studies are commonly used to identify conditions like peripheral neuropathy1 and nerve compression syndromes2. By measuring the flow of electrical signals through motor nerves (which control muscles and movement) and sensory nerves (which relay information about touch, taste, smell, and vision), an NCS can reveal the cause, severity, and prognosis of this nerve damage.
Healthcare providers may recommend an NCS if symptoms such as tingling or numbness3 in arms, legs, hands, feet, or face appear. They may also be alongside an EMG. The test can be conducted in an outpatient setting or during a hospital stay and provides valuable information for diagnosing, determining the severity, and guiding treatment for nerve-related conditions.
Peripheral neuropathy
Peripheral neuropathy occurs when peripheral nerves become damaged. Various conditions can lead to this damage, and the effects can vary depending on the cause and the specific nerves affected.
Some common causes of peripheral neuropathy include:
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Diabetes4
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Vitamin deficiencies
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Thyroid
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Alcohol use disorder
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Certain autoimmune conditions, like lupus, rheumatoid arthritis, Sjögren syndrome, vasculitis, and Guillain-Barré syndrome
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Infections from viruses, such as HIV, or bacteria (such as Borrelia burgdorferi, which cause Lyme disease)
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Medications, such as chemotherapy
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Direct injury to your nerves from trauma or surgery
Nerve compression syndromes
Nerve compression syndrome can occur when pressure is applied to a peripheral nerve. It can lead to peripheral neuropathy. Examples of nerve compression syndromes include:
- Carpal tunnel syndrome
- Sciatica
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Radial tunnel syndrome
- Thoracic outlet syndrome
- Meralgia paresthetica
EMG Test Vs. Nerve Conduction Test
Although they often occur together, an EMG and nerve conduction test are different and have different uses.
An EMG test measures the muscle's response to the nerve signal and the amount of electrical activity the muscle contraction produces.
A nerve conduction study detects the flow of electrical current through the nerve before it reaches your muscle. It is used to diagnose conditions that cause nerve damage. It is also helpful in evaluating peripheral nerves located outside of the central nervous system.
Why is An EMG Test Performed?
An EMG test may be used for muscle pain, weakness, or abnormal sensation symptoms. The following symptoms may occur with diseases that cause muscle or nerve damage:
- Numbness
- Muscle weakness
- Muscle cramping or pain
- Tingling
- Muscle twitching
- Paralysis
These symptoms can develop due to an injury or disorder related to the nerves or the muscles. An EMG test can help differentiate between muscle weakness caused by a nervous system disorder and an injury to a nerve attached to the muscle.
What is an EDX Test Used to Diagnose?
An EDX test can help diagnose conditions that cause muscle dysfunction, nerve dysfunction, or problems with the signal transmission from the nerves to the muscle. These may include neuromuscular diseases, nerve disorders, and conditions that affect the motor neurons in the brain and spinal cord.
There are many different forms of neuromuscular diseases. The prevalence of neuromuscular disease is about 1 in 3,5004.
Some of the conditions an EDX test may help diagnose include the following:
Carpal tunnel syndrome: Carpal tunnel syndrome occurs when the medial nerve in the hand is compressed or squeezed as it travels through the wrist. It causes tingling, numbness, and pain in the hand and forearm.
Nerve compression syndromes: This syndrome can develop when pressure is applied to nerves within the peripheral nervous system. These nerves are connected to various body parts, such as the feet and hands, and can lead to significant pain.
Peripheral neuropathy: This is a condition that causes nerve damage to the nerves located outside of the spinal cord and brain.
Muscular dystrophy: Muscular dystrophy involves a group of diseases that lead to progressive muscle weakness and a decrease in muscle mass.
Polymyositis: Polymyositis is a rare condition caused by the immune system attacking the muscles. It causes weakness and inflammation in the muscles.
Myasthenia gravis: This chronic autoimmune condition affects communication between muscles and nerves, leading to muscle weakness.
Amyotrophic lateral sclerosis (ALS): Also known as Lou Gehrig's disease, this condition affects the motor neurons in your spinal cord and brain.
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How is an EMG Test Performed?
An EMG procedure is performed in a healthcare professional’s office.
Your physician will clean the area with an antiseptic before the procedure to reduce the risk of infection.
To perform an EMG test, the physician inserts a needle electrode sensor through the skin into the muscle tissue. You may be asked to move into different positions during the procedure.
The electrode picks up and records the electrical signals given off by the muscle. The electrical activity is transmitted to a nearby monitor for your doctor to view while the procedure is performed.
Once the electrodes are placed in your muscle, your healthcare provider may ask you to contract the muscle. For instance, you may be asked to bend your arm or straighten your leg.
The electrical activity your physician will watch on the monitor provides information about the muscle's ability to respond to the nerves.
Once the test is completed, the doctor will remove the needle from your muscle tissue.
How Do You Prepare for an EMG Test?
In general, not much preparation is required before an EMG test. Patients are provided with specific instructions to follow and may be asked about prescription drugs, over-the-counter medications, and herbal supplements being taken that may increase the risk of bleeding. For example, if you are taking blood thinners, the doctor must determine if you can still have the procedure.
It is also essential to inform the physician of any bleeding disorder. Individuals with implantable defibrillators or pacemakers should discuss that with their physician. You may not be able to have an EMG if you have these devices.
Before An EMG Scan
Usually, no special preparation is needed on the day of your test. However, you may be instructed not to wear any lotions, creams, or oils on the day of the test.
It is also helpful to wear comfortable, loose clothing that doesn't obstruct the muscle the physician evaluates. However, in some cases, you may be asked to change into a hospital gown before the procedure.
What Can You Expect After an EMG Nerve Test?
When the electrode needle is inserted, some discomfort may occur. However, the test uses a very thin needle, so the pain is mild. Most patients tolerate the test without issues.
After the procedure, the muscle may experience soreness or bruising for a few days.
The doctor may discuss the results immediately after the procedure. If the EMG test shows electrical activity in a resting muscle, a disorder may be affecting the nerves that connect to the muscle, or inflammation due to an injury may be present.
The physician may discuss additional recommended tests or treatments depending on the results.
Are There Risks with an EMG Test?
An EMG is a low-risk test. Most patients do not have any complications. Muscle soreness may last a few days. It is typically mild and can be relieved with an over-the-counter pain reliever.
Although uncommon, swelling, bruising, and tingling can occur at the needle insertion site. If you experience any symptoms of an infection, such as significant pain or swelling, it's essential to inform your physician immediately.
Conclusion
EMG tests are often performed in conjunction with nerve conduction studies. Combining these two tests can help doctors diagnose various injuries and muscle and nerve disorders.
If you have any questions about an EMG or symptoms of muscle or nerve disorder, we are happy to help. If you would like to schedule a consultation, please contact us online or call 480-573-0130
today!
- Cleveland Clinic. “Peripheral Neuropathy: What It Is, Symptoms & Treatment.” Cleveland Clinic, Cleveland Clinic, 14 Oct. 2022, my.clevelandclinic.org/health/diseases/14737-peripheral-neuropathy
- Cleveland Clinic. “Nerve Compression Syndromes: Causes, Treatment & Prevention.” Cleveland Clinic, 23 Nov. 2021, my.clevelandclinic.org/health/diseases/22137-nerve-compression-syndrome
- “Numbness (Paresthesia and Neuropathy).” Cleveland Clinic, 21 Aug. 2023, my.clevelandclinic.org/health/symptoms/21015-numbness
- Emery, A. E. (1991). Population frequencies of inherited neuromuscular diseases—a world survey. Neuromuscular disorders, 1(1), 19-29.https://www.sciencedirect.com/science/article/abs/pii/096089669190039U#:~:text=A%20conservative%20estimate%20of%20the,childhood%20or%20in%20later%20life.
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