Electromyography
EMG; Myogram; Electromyogram
Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.
How the Test is Performed
The health care provider inserts a very thin needle electrode through the skin into the muscle. The electrode on the needle picks up the electrical activity given off by your muscles. This activity appears on a nearby monitor, and may be heard through a speaker.
After placement of the electrodes, you may be asked to contract the muscle. For example, by bending your arm. The electrical activity seen on the monitor provides information about your muscle's ability to respond when the nerves to your muscles are stimulated.
A nerve conduction velocity test is almost always performed during the same visit as an EMG.
Nerve conduction velocity
Nerve conduction velocity (NCV) is a test to see how fast electrical signals move through a nerve.
How to Prepare for the Test
No special preparation is usually necessary. Avoid using any creams or lotions on the day of the test.
Body temperature can affect the results of this test. If it is extremely cold outside, you may be told to wait in a warm room for a while before the test is performed.
If you are taking blood thinners or anticoagulants, inform the provider performing the test before it is done.
How the Test will Feel
You may feel some pain or discomfort when the needles are inserted. But most people are able to complete the test without problems.
Afterward, the muscle may feel tender or bruised for a few days.
Why the Test is Performed
EMG is most often used when a person has symptoms of weakness, pain, or abnormal sensation. It can help tell the difference between muscle weakness caused by the injury of a nerve attached to a muscle, and weakness due to nervous system disorders, such as muscle diseases.
Normal Results
There is normally very little electrical activity in a muscle while at rest. Inserting the needles can cause some electrical activity, but once the muscles quiet down, there should be little electrical activity detected.
When you flex a muscle, activity begins to appear. As you contract your muscle more, the electrical activity increases and a pattern can be seen. This pattern helps your doctor determine if the muscle is responding as it should.
What Abnormal Results Mean
An EMG can detect problems with your muscles during rest or activity. Disorders or conditions that cause abnormal results include the following:
-
Alcoholic neuropathy
(damage to nerves from drinking too much alcohol)
Alcoholic neuropathy
Alcoholic neuropathy is damage to the nerves that results from excessive drinking of alcohol.
-
Amyotrophic lateral sclerosis
(ALS; disease of the nerve cells in the brain and spinal cord that control muscle movement)
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis, or ALS, is a disease of the nerve cells in the brain, brain stem and spinal cord that control voluntary muscle movemen...
-
Axillary nerve dysfunction
(damage of the nerve that controls shoulder movement and sensation)
Axillary nerve dysfunction
Axillary nerve dysfunction is nerve damage that leads to a loss of movement or sensation in the shoulder.
-
Becker muscular dystrophy
(muscle weakness of the legs and pelvis)
Becker muscular dystrophy
Becker muscular dystrophy is an inherited disorder that involves slowly worsening muscle weakness of the legs and pelvis.
-
Brachial plexopathy
(problem affecting the set of nerves that leave the neck and enter the arm)
Brachial plexopathy
Brachial plexopathy is a form of peripheral neuropathy. It occurs when there is damage to the brachial plexus. This is an area on each side of the ...
-
Carpal tunnel syndrome
(problem affecting the median nerve in the wrist and hand)
Carpal tunnel syndrome
Carpal tunnel syndrome is a condition in which there is excessive pressure on the median nerve. This is the nerve in the wrist that allows feeling a...
-
Cubital tunnel syndrome
(problem affecting the ulnar nerve in the elbow)
Cubital tunnel syndrome
Ulnar nerve dysfunction is a problem with the nerve that travels from the shoulder to the hand, called the ulnar nerve. It helps you move your arm, ...
-
Cervical spondylosis
(neck pain from wear on the disks and bones of the neck)
Cervical spondylosis
Cervical spondylosis is a disorder in which there is wear on the cartilage (disks) and bones of the neck (cervical vertebrae). It is a common cause ...
-
Common peroneal nerve dysfunction
(damage of the peroneal nerve leading to loss of movement or sensation in the foot and leg)
Common peroneal nerve dysfunction
Common peroneal nerve dysfunction is damage to the peroneal nerve leading to loss of movement or sensation in the foot and leg.
- Denervation (reduced nerve stimulation of a muscle)
-
Dermatomyositis
(muscle disease that involves inflammation and a skin rash)
Dermatomyositis
Dermatomyositis is a muscle disease that involves inflammation and a skin rash. It is a type of inflammatory myopathy.
-
Distal median nerve dysfunction
(problem affecting the median nerve in the arm)
Distal median nerve dysfunction
Distal median nerve dysfunction is a form of peripheral neuropathy that affects the movement of or sensation in the hands. A common type of distal me...
-
Duchenne muscular dystrophy
(inherited disease that involves muscle weakness)
Duchenne muscular dystrophy
Duchenne muscular dystrophy is an inherited disorder. It involves muscle weakness, which quickly gets worse.
-
Facioscapulohumeral muscular dystrophy
(Landouzy-Dejerine; disease of muscle weakness and loss of muscle tissue)
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral muscular dystrophy is muscle weakness and loss of muscle tissue that gets worse over time.
-
Familial periodic paralysis
(disorder that causes muscle weakness and sometimes a lower than normal level of potassium in the blood)
Familial periodic paralysis
Hypokalemic periodic paralysis (hypoPP) is a disorder that causes occasional episodes of muscle weakness and sometimes a lower than normal level of p...
-
Femoral nerve dysfunction
(loss of movement or sensation in parts of the legs due to damage to the femoral nerve)
Femoral nerve dysfunction
Femoral nerve dysfunction is a loss of movement or sensation in parts of the legs due to damage to the femoral nerve.
-
Friedreich ataxia
(inherited disease that affects areas in the brain and spinal cord that control coordination, muscle movement, and other functions)
Friedreich ataxia
Friedreich ataxia is a rare disease passed down through families (inherited). It affects the muscles and heart.
-
Guillain-Barré
syndrome (autoimmune disorder of the nerves that leads to muscle weakness or paralysis)
Guillain-Barré
Guillain-Barré syndrome is a serious health problem that occurs when the body's defense (immune) system mistakenly attacks part of the nervous system...
-
Lambert-Eaton syndrome
(autoimmune disorder of the nerves that causes muscle weakness)
Lambert-Eaton syndrome
Lambert-Eaton syndrome (LES) is a rare disorder in which faulty communication between nerves and muscles leads to muscle weakness.
-
Multiple mononeuropathy
(a nervous system disorder that involves damage to at least 2 separate nerve areas)
Multiple mononeuropathy
Multiple mononeuropathy is a nervous system disorder that involves damage to at least 2 separate nerve areas.
-
Mononeuropathy
(damage to a single nerve that results in loss of movement, sensation, or other function of that nerve)
Mononeuropathy
Mononeuropathy is damage to a single nerve, which results in loss of movement, sensation, or other function of that nerve.
-
Myopathy (muscle degeneration caused by a number of disorders, including
muscular dystrophy
)
Muscular dystrophy
Muscular dystrophy is a group of inherited disorders that cause muscle weakness and loss of muscle tissue, which get worse over time.
-
Myasthenia gravis
(autoimmune disorder of the nerves that causes weakness of the voluntary muscles)
Myasthenia gravis
Myasthenia gravis is a neuromuscular disorder. Neuromuscular disorders involve the muscles and the nerves that control them.
-
Peripheral neuropathy
(damage of nerves away from the brain and spinal cord)
Peripheral neuropathy
Peripheral nerves carry information to and from the brain. They also carry signals to and from the spinal cord to the rest of the body. Peripheral n...
-
Polymyositis
(muscle weakness, swelling, tenderness, and tissue damage of the skeletal muscles)
Polymyositis
Polymyositis is a rare inflammatory disease. It leads to muscle weakness, swelling tenderness, and tissue damage. It is part of a larger group of d...
-
Radial nerve dysfunction
(damage of the radial nerve causing loss of movement or sensation in the back of the arm or hand)
Radial nerve dysfunction
Radial nerve dysfunction is a problem with the radial nerve. This is the nerve that travels from the armpit down the back of the arm to the hand. I...
-
Sciatic nerve dysfunction
(injury to or pressure on the sciatic nerve that causes weakness, numbness, or tingling in the leg)
Sciatic nerve dysfunction
Sciatica refers to pain, weakness, numbness, or tingling in the leg. It is caused by injury to or pressure on the sciatic nerve. Sciatica is a symp...
-
Sensorimotor polyneuropathy
(condition that causes a decreased ability to move or feel because of nerve damage)
Sensorimotor polyneuropathy
Sensorimotor polyneuropathy is a condition that causes a decreased ability to move or feel (sensation) because of nerve damage.
-
Shy-Drager syndrome
(nervous system disease that causes bodywide symptoms)
Shy-Drager syndrome
Multiple system atrophy (MSA) is a rare condition that causes symptoms similar to Parkinson disease. However, people with MSA have more widespread d...
-
Thyrotoxic periodic paralysis
(muscle weakness from high levels of thyroid hormone)
Thyrotoxic periodic paralysis
Thyrotoxic periodic paralysis is a condition in which there are episodes of muscle weakness. It occurs in people who have high levels of thyroid hor...
-
Tibial nerve dysfunction
(damage of the tibial nerve causing loss of movement or sensation in the foot)
Tibial nerve dysfunction
Tibial nerve dysfunction is a loss of movement or sensation in the foot from damage to the tibial nerve.
Risks
Risks of this test include:
- Bleeding (minimal)
- Infection at the electrode sites (rare)
References
Chernecky CC, Berger BJ. Electromyography (EMG) and nerve conduction studies (electromyelogram)-diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures . 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:468-469.
Katirji B. Clinical electromyography. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice . 7th ed. Philadelphia, PA: Elsevier; 2016:chap 35.
-
Electromyography - illustration
Electromyography is a test that measures muscle response to nervous stimulation. A needle electrode is inserted through the skin into the muscle. Each muscle fiber that contracts will produce an action potential. The presence, size, and shape of the wave form of the action potential produced on the oscilloscope, provides information about the ability of the muscle to respond to nervous stimulation.
Electromyography
illustration
-
Electromyography - illustration
Electromyography is a test that measures muscle response to nervous stimulation. A needle electrode is inserted through the skin into the muscle. Each muscle fiber that contracts will produce an action potential. The presence, size, and shape of the wave form of the action potential produced on the oscilloscope, provides information about the ability of the muscle to respond to nervous stimulation.
Electromyography
illustration
Review Date: 5/30/2016
Reviewed By: Amit M. Shelat, DO, FACP, Attending Neurologist and Assistant Professor of Clinical Neurology, SUNY Stony Brook, School of Medicine, Stony Brook, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.