Electromyography or EMG is a diagnostic test used to evaluate the electrical activity in your nerves as they transmit messages to your muscles when the muscles are contracting and when they’re at rest. The purpose of an EMG is to assess the health of your muscles and the nerves that control them. During an Electromyography , a thin needle with an electrode is inserted through your skin into a muscle. The electrode records the electrical activity in your nerve and muscle and transmits it to a receiver that displays the electromyography results on a printout or on a computer screen. The electrical activity recorded during an electromyography may also be broadcast over a speaker for your physician to hear.
An EMG can help diagnose disorders that affect muscle and nerve function, such as muscular dystrophies, and nerve disorders, such as neuropathies.
The activity of your muscles and the nerves that control them produce electrical signals. A healthy, relaxed muscle is electrically silent. When you contract your muscle, the nerves create a pattern of electrical signals that cause your muscle to respond. An electromyography records this electrical pattern. If the electrical pattern is abnormal when the muscle is at rest or when a nerve is stimulated, it may indicate a problem with the nerve or muscle. Results from electromyography can help diagnose a condition that interferes with muscle contractions. These conditions include:
- Diseases that affect the muscle, such as muscular dystrophies
- Diseases that affect the connection between the nerve and the muscle (neuromuscular junction), such as myasthenia gravis
- Diffuse nerve disorders that cause peripheral neuropathy
- Disorders that affect the motor neurons (anterior horn cells) in the spinal cord, such as amyotrophic lateral sclerosis or a ruptured spinal disk
To provide a more complete picture of your nerve function, an electromyography is done in conjunction with a nerve conduction study. Using electrodes on the surface of your skin, this test measures the strength and speed of the electrical signals as they travel through your nerves to the muscles. Used along with an electromyography , nerve conduction studies can help diagnose disorders that affect nerve function, such as Charcot-Marie-Tooth disease. nitially, a technician will place electrodes on the surface of your skin and stimulate the nerve with a small electrical stimulus that will make your muscles twitch. This twitch will be measured by the computer. A physician will then insert a thin, sterile needle electrode through your skin into the muscle to detect electrical activity in your nerve and muscle. During the exam, the electrical activity is displayed on a printout or computer screen and broadcast over a speaker. After the electrode is in place, you may be asked to contract the muscle. The electrical activity produced when you do so will provide information about the muscle’s ability to respond when the nerve is stimulated. Electromyography can be uncomfortable, as the needle electrode may cause muscle pain. But, the pain is usually limited and goes away soon after the needle is removed from your muscle.
You may experience some temporary, minor bruising where the needle was inserted into your muscle. This bruising should fade within several days.
Electromyography is a low-risk procedure. Complications are rare, but there’s a very small risk of bleeding, infection and nerve injury where the electrode is inserted. When examining muscles along the chest wall, there’s also a very small risk that it could cause air to leak into the area between your lungs and chest wall, causing your lung to collapse (pneumothorax).
The results of an EMG usually are ready soon after the test is complete. But a physician, or neurologist, must analyze and interpret them. Your physician will discuss the test results with you and next steps, if necessary, at a follow-up appointment.