Also called: Myogram, EMG, Electromyography, EMG Test
An electromyogram (EMG) is a procedure that tests the electrical activity of a muscle in response to nerve stimulation. The results of this test help physicians to determine the health of a patient’s muscles and nerves. An EMG is most often used to diagnose the source of symptoms such as pain or weakness in the muscles or numbness in parts of the body.
An EMG may be performed in a hospital, clinic or physician’s office. Preparation for
the test is usually minimal, and patients are urged to follow the recommendations of their physician. In general, patients may be advised not to consume caffeine or use tobacco products for up to three hours prior to the EMG. In addition, certain information should be provided to a physician prior to the EMG.
In most cases, an EMG involves inserting a needle electrode into the muscle to be tested. Patients will be asked to contract a muscle (i.e., bend an arm or leg, or make a fist). When this occurs, nerves in the area send signals to the muscles to move. Each muscle fiber that contracts produces electrical activity of its own. This activity is detected and recorded by the needle electrode. The electrical activity of a muscle at rest will also be recorded by the needle electrode (although no activity should occur in a normal muscle at rest).
Needle electrodes may be repositioned during an EMG to different areas of a certain muscle, or into different nearby muscles.
Muscle activity during the test will appear as wavy lines on a special monitor. The presence, size and shape of the waves reveals information about the muscle’s response to nerve stimulation. Sometimes this activity is measured audibly through a speaker. In these cases, rapid-fire popping sounds may be heard when a muscle contracts.
In addition to an EMG, a nerve conduction velocity (NCV) test may also be performed. A NCV records the speed of impulses through a nerve. This test identifies how well certain nerves pass electrical signals. A NCV may help identify whether a patient’s symptoms may be due to problems with a particular nerve.
EMG results are typically available immediately, but they usually need to be interpreted and analyzed by a specialist (e.g., a neurologist) before a proper diagnosis can be made. As a result, it may take a day or two before a patient receives the test results. Typically, there are very few risks associated with an EMG. Some patients may find that the insertion of needle electrodes produces discomfort similar to that of an intramuscular injection. In addition, muscles tested during an EMG may be sore for a few days following the test. Patients may also experience minor bruising in the area. There is a slight risk of bleeding or infection at the needle insertion site following the procedure.
An electromyogram (EMG) is a procedure that tests the health of skeletal muscles (muscles attached to bone that control posture and movement) and the nerves that control them. EMGs measure the electrical activity of a muscle in response to nerve stimulation.
The nature and speed of impulse conduction along a nerve may also be measured during what is typically a companion test to the EMG, a nerve conduction velocity (NCV) test. According to the American Academy of Neurology (AAN), EMGs performed with needle electrodes, together with NCVs, represent the gold standard for diagnosing neuromuscular disorders.
Nerves and muscles work together to allow the body to perform everyday tasks. Motor nerves send signals that stimulate the muscles. This generates electrical activity inside the muscle, causing it to contract. This tightening of the muscle generates electrical activity of its own.
In most cases, an EMG involves inserting a thin needle electrode into skeletal muscles. Patients are asked to contract a muscle, and the electrical activity of the muscle in response is recorded by the electrode and transmitted to a receiving device. This muscle activity is then graphically displayed on a special monitor (oscilloscope). It may also be heard and monitored through a speaker.
EMGs are most often used to help diagnose the cause of certain symptoms, such as pain or weakness in the muscles or numbness in parts of the body. Through this test, a physician often is able to establish whether a patient’s muscle weakness is a result of a problem with the muscle itself, or a byproduct of a neurological disorder. An EMG and NCV can help a physician determine whether the source of the problem is with a muscle, nerve or the neuromuscular junction (connection between a nerve fiber and the muscle it supplies).
The accuracy of EMGs may be limited by certain factors. If a patient’s hands or feet are cool, this may affect EMG results and result in the wrong diagnosis. EMGs may also be difficult to perform on patients who are obese. Furthermore, professionals may have limited training or experience in performing EMGs.
If a patient’s symptoms are related to a recent injury, a physician may schedule the EMG to take place several weeks later. Muscle activity affected by an injury may not show up in an EMG for up to three weeks after the injury.
Aside from the standard EMG, there are various other types of EMG. Two of the most common types are the single-fiber EMG and the surface EMG (SEMG).
A single-fiber EMG is a type of EMG that concentrates on a specific muscle fiber, rather than the entire muscle. It uses very small needle electrodes and its results are generally more sensitive than the standard EMG. This type of EMG may be used when certain disorders are suspected (e.g., myasthenia gravis) that may not be identified with a standard EMG. Single-fiber EMGs may only be available in specialized laboratories.
A noninvasive type of EMG called a surface EMG (SEMG) may sometimes be performed. No needles are used in this type of EMG. Instead, surface electrodes are placed on the skin overlying the muscle to record muscular activity. SEMG results are not as reliable as those of a needle EMG, and the clinical value of the SEMG has not been well established. For example, SEMGs are not considered an acceptable method of diagnosing neuromuscular disorders, according to the AAN and American Association of Neuromuscular and Electrodiagnostic Medicine. SEMGs are more likely to be used in rehabilitation centers and similar healthcare settings to measure muscle activity (i.e., whether a muscle is being used in exercise). SEMGs may also be used in biofeedback.
Depending on the results of the EMG and NCV tests, additional tests (e.g., blood tests, muscle biopsy) may be recommended by a physician.
Conditions diagnosed with electromyograms
In many cases, an electromyogram (EMG) by itself is not usually enough to diagnose a medical condition. However, an EMG can be invaluable when combined with information from other sources, including physical examinations, neurological examinations and medical histories. EMGs are frequently used along with nerve conduction velocity tests.
An EMG may be performed prior to diagnosing many different neurological conditions, including:
- Amyotrophic lateral sclerosis (ALS). A degenerative disease characterized by muscle weakness. ALS is also known as Lou Gehrig’s disease.
- Carpal tunnel syndrome. Considered a type of focal neuropathy that involves compression of a nerve in the wrist. Symptoms include pain or numbness in the wrist or hand.
- Cervical spondylosis. Arthritis of the neck that may include abnormal growths on the vertebrae of the cervical spine. Symptoms include neck stiffness as well as pain or weakness in the arm or shoulder.
- Guillain-Barre syndrome. A rare condition in which nerve damage inhibits muscle movement. Loss of mobility is usually temporary, although paralysis and death may occur in a small number of cases.
- Myasthenia gravis. An autoimmune disorder that causes muscle weakness. Symptoms worsen with activity and improve after rest.
- Myopathy. A disease that causes progressive muscle weakness. Polymyositis is a type of inflammatory myopathy that causes inflammation of muscle tissue and is believed to be caused by autoimmune dysfunction. Muscular dystrophy is a type of myopathy that is caused by an inherited or spontaneous genetic mutation.
- Neuropathy. Nerve damage that affects nerve and muscle functioning. Major categories of neuropathies include focal neuropathy (localized nerve damage, such as a pinched nerve due to a herniated disc), peripheral neuropathy (nerve damage that affects the limbs) and autonomic neuropathy (nerve damage affecting involuntary body processes and internal organs).
Neuropathies may affect different areas of the body, depending on the nerves involved. For example, brachial plexopathy involves damage to the nerves of the brachial plexus in the shoulder and arm. Axillary nerve dysfunction involves the axillary nerve of the shoulder, and tibial nerve dysfunction involves nerve damage in the leg.
Neuropathies may also be caused by many different conditions such as alcohol abuse (alcoholic neuropathy) and diabetes (diabetic neuropathy). In many cases, the cause of a patient’s neuropathy is unknown.
- Neurosarcoidosis. Disease in which abnormal collections of inflammatory cells form in the tissue of the nervous system, including the brain, spinal cord and other nerves. Symptoms may include facial weakness, muscle weakness and sensory loss.
In addition, EMGs may be used in patients with urinary or bowel incontinence (a symptom of many different conditions, including neurological disorders such as multiple system atrophy and autonomic neuropathy). In these cases, the EMG tests the muscle and nerve function of the external urinary and/or anal sphincters (the ringlike band of muscles that help control bladder and bowel function).
Before the electromyogram
The preparation required of a patient before an electromyogram (EMG) is usually minimal. Patients are urged to follow recommendations made by their physician.
Prior to the test, a physician is likely to perform a physical examination, neurological examination and obtain a medical history of the patient. The following physical characteristics are likely to be checked:
- Blood pressure and heart rate
- Muscle strength
- Sensitivity to position, vibration, temperature and light touch
Patients are generally advised not to consume caffeine or use tobacco products for up to three hours prior to the EMG. Anything that constricts a patient’s blood vessels (such as caffeinated beverages or tobacco products) can restrict the level of nutrients normally supplied through the blood to the peripheral nerves. This may result in inaccurate EMG results, and may potentially worsen a patient’s symptoms. In addition, patients are urged to wear loose-fitting clothing that permits easy access to the muscles to be tested.
Certain medical information should be disclosed to a physician before an EMG, including:
- Current medications. Certain medications that affect the nervous system may interfere with the ability to get an accurate reading from an EMG. These include muscle relaxants and anticholinergics, which inhibit transmission of nerve impulses. Patients should also inform their physician of the use of anticoagulants, including aspirin, which are commonly taken for heart conditions. These medications may increase the risk of bleeding at the injection site.
- History of bleeding problems. People with bleeding problems may have an increased risk of bleeding at the needle site.
- Pacemakers and implantable defibrillators. EMGs are generally considered safe, even for patients with these implanted devices. However, these devices may affect how a nerve conduction velocity test (which commonly accompanies an EMG) is conducted.
Patients may be asked to avoid using any creams or lotions on the day of the test, as these could interfere with test results. Children may need extra parental attention and support to calm fears about the testing. It is best to be honest with children and to warn them that the test may involve minor discomfort or pain.
During and after the electromyogram
An electromyogram (EMG) may be performed in a hospital, clinic or physician’s office. Immediately prior to the test, an antiseptic solution is used to clean the area to be tested. Patients may be asked to lay on a table or bed or recline in a chair so that the muscles being tested are relaxed and accessible.
In most cases, a needle electrode will be inserted into the muscle to be tested. Wires attached to the needle connect it to a recording device. Patients may feel slight discomfort during needle insertion.
Once the needle electrode is in place, the activity of the resting muscle is recorded and displayed on a monitor called an oscilloscope. Muscle tissue is electrically silent at rest, so no activity should appear on the recording at first. If activity occurs while muscles are at rest, it may indicate a problem with the nerves supplying that muscle, or inflammation or disease of muscle tissue.
Patients may then be asked to contract certain muscles, such as bending an arm or leg, or making a fist. Each muscle fiber that contracts produces electrical activity. The electrical activity produced is graphically displayed in wave-like form on the oscilloscope. The morphology (shape) of these waves reveal information about the muscle’s response to nerve stimulation. In some cases, the activity is measured audibly through a speaker. As the muscle contracts, rapid-fire popping sounds may be heard. Abnormal levels of activity may indicate various muscle or nerve disorders.
An EMG usually takes between 30 and 60 minutes. Once the test is finished, the needle electrodes are removed and the skin is cleaned. The muscles involved in the testing may be tender or bruised for a few days afterward. Over-the-counter (OTC) pain medications may alleviate any lingering pain, although patients should consult their physician before taking any type of medication, including OTC remedies.
Although the results of an electromyography (EMG) are typically available right away, they usually need to be read by a specialist (e.g., a neurologist) before the information can be properly interpreted, analyzed and a diagnosis made. Thus, it may take a day or two before a patient receives the test results.
Potential risks with electromyograms
Typically, there are very few risks associated with electromyogram (EMG). Some patients may find that the insertion of the needle electrode produces discomfort similar to that of an intramuscular injection.
Muscles involved in the test may be sore and bruising may occur for a few days following the test. There is a slight risk of bleeding and infection at the insertion sites following the procedure.
Patients should call their physician if the following signs or symptoms appear at insertion sites and either increase in severity or persist for a long period of time:
Patients should be aware that trauma caused to the muscle during an EMG may temporarily raise the levels of certain enzymes in the body (e.g., aldolase, lactate dehydrogenase, creatine phosphokinase). This can affect the results of muscle biopsies, blood tests and other tests for up to 10 days after the EMG. Patients should consult the physician about the timing of other tests after an EMG.
Questions for your doctor on electromyogram
Preparing questions in advance can help patients to have more meaningful discussions regarding their healthcare. Patients may wish to ask their doctor the following questions related to electromyogram (EMG):
- When and where will my test take place? How long will it take? Who will perform it?
- How do I prepare for this test? Do I need to abstain from anything (e.g., caffeinated beverages, tobacco products) prior to the test? For how long?
- What should I expect during the test? Is it likely to be painful?
- When will the results be ready, and who will explain them to me?
- What do the results of my test show?
- Do I need additional tests or treatments?
- At what point should I contact you if I have pain or other side effects after an EMG?
- Do I need to avoid blood tests, biopsies or other assessments for a certain period after having an EMG?
- How often should I have an EMG?
- Can EMG biofeedback ease my neuropathic pain, musculoskeletal condition, high blood pressure or other condition? If so, can you recommend a biofeedback therapist?