Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.
EMG; Myogram; Electromyogram
How the Test is Performed
The health care provider will insert 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.
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, wait in a warm room for a while before the test is performed.
If you are taking blood thinners or anticoagulants, inform the person 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.
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
- Amyotrophic lateral sclerosis (ALS)
- Axillary nerve dysfunction
- Becker muscular dystrophy
- Brachial plexopathy
- Carpal tunnel syndrome
- Cubital tunnel syndrome
- Cervical spondylosis
- Common peroneal nerve dysfunction
- Denervation (reduced nerve stimulation of a muscle)
- Distal median nerve dysfunction
- Duchenne muscular dystrophy
- Facioscapulohumeral muscular dystrophy (Landouzy-Dejerine)
- Familial periodic paralysis
- Femoral nerve dysfunction
- Friedreich ataxia
- Guillain-Barre syndrome
- Lambert-Eaton syndrome
- Mononeuritis multiplex
- Myopathy (muscle degeneration caused by a number of disorders, including muscular dystrophy)
- Myasthenia gravis
- Peripheral neuropathy
- Radial nerve dysfunction
- Sciatic nerve dysfunction
- Sensorimotor polyneuropathy
- Shy-Drager syndrome
- Thyrotoxic periodic paralysis
- Tibial nerve dysfunction
This list is not all-inclusive.
- Bleeding (minimal)
- Infection at the electrode sites (minimal risk)
Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 403.
Katirji B. Clinical neurophysiology: clinical electromyography. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC, eds. Bradley's Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Saunders Elsevier; 2012:chap 32B.