Electromyography (ee-LECK-tro-my-AH-graf-ee), or EMG, is a test that is used to check the health of the muscles and nerves inside your body.
Nerves that control your muscles are also called motor neurons (NUR-ons), and they work by transmitting electrical signals to your muscles that tell them when to contract, or squeeze.
An EMG test uses these electrical signals to test the health of your muscles and nerves by measuring them, then turning these signals into a graph, or sounds, that can be read by a specialist. An EMG can determine nerve or muscle dysfunction, or other problems with signals that communicate from nerves to muscles.
An EMG test uses tiny devices, called electrodes, to give off or detect electrical signals. During the EMG test, a needle that has an electrode on the end of it will be put into the muscle and used to record that muscle’s activity.
Your doctor may request that you take an EMG test if you have certain symptoms that are usually present with a muscle or nerve disorder. These symptoms include:
- Muscle weakness
- Muscle pain
The doctor will use your EMG results to help diagnose or rule out certain nerve or muscle conditions, such as:
- Nerve root disorders, like a herniated disk in the spine
- Diseases that affect connections between the muscles and nerves, including myasthenia gravis (my-as-THEE-nee-ah GRAV-iss)
- Disorders of the spinal cord or motor neurons in the brain, like polio
- Nerve disorders (other than nerves inside the spinal cord, also called peripheral [peh-RIH-fur-al] nerves), like carpal tunnel syndrome
- Muscular disorders, such as polymyositis (PAH-lee-my-oh-SYE-tiss) or muscular dystrophy
Usually a nerve conduction velocity test will be done in the same visit as an EMG test. The nerve conduction study uses electrodes that are taped to your skin to measure things like the speed and strength of the electrical signals as they move from point to point inside your body.
An EMG test is a low-risk, routine procedure that rarely has complications. However, there is a small risk of infection, excessive bleeding, or nerve injury in the place where the needle electrode was inserted.
Very rarely, when an EMG is done on the muscles along the chest wall, air could leak into the area between the chest and the chest wall. This air leak may cause a lung to collapse. The risk of this happening is very small, but still possible.
There is also a small chance that an EMG test could interfere with the functionality of cardiac pacemakers and implanted cardioverter defibrillators (ICDs). Make sure your doctor knows if you have either of these devices to help evaluate if this is the best procedure for you.
If you have lymphedema (lim-fuh-DEEM-ah), there is some small risk that an EMG in the affected area could worsen the condition. Make sure your doctor knows you have this condition to help determine if an EMG is the best option for you.
An EMG is helpful to diagnose muscle and nerve disorders without requiring surgery.
Your EMG test will be performed by a nervous system specialist, called a neurologist [nu-RALL-oh-jist]. Tell your neurologist if:
- You have a pacemaker or other electrical device in your body
- You have hemophilia, a disorder that causes difficulty with blood-clotting and sometimes excessive bleeding
- You take blood thinners, including acetaminophen (such has Tylenol)
To prepare for your test, make sure to take a shower or bath to remove oils from your skin. Do not put on any lotion or cream before your test.
If you smoke, it is important for you to avoid smoking for at least 3 hours before your test.
Make sure to wear comfortable clothing that does not obstruct the area your neurologist will be testing. You may also be asked to change into a hospital gown before your test.
Tell your doctor, as well as the neurologist, about any over-the-counter or prescription medications you are taking.
When you schedule your EMG test, you may also ask the scheduler what time you should arrive, how to get to the lab, and if you can bring a friend or relative with you to the test.
A neurologist will give you your EMG test. Before the exam, you may be asked to change into a hospital gown and lie down on an examination table.
Usually a nerve conduction study will be performed with the EMG test. If this test will be performed with your EMG, it will usually be performed before the EMG test.
For the nerve conduction study, the neurologist or technician will place electrodes, which look like small stickers with wires coming out of them, on your skin in various places, depending on where you have symptoms.
The electrodes on your skin will give off tiny electrical pulses that may feel like a muscle twinge or muscle spasm. It is usually not painful. Once the test is complete, the electrodes will be removed.
For the EMG test, your neurologist will clean the affected area with an antiseptic. They will then insert the very thin electrode needle at different locations on your body, depending on your symptoms.
The electrode needle may cause some pain or discomfort, especially during insertion, but sometimes throughout the procedure. This pain or discomfort should end as soon as the needle is removed. If you are worried about the pain, you can ask your neurologist to let you take a short break during the test.
During the test, your neurologist will ask you to periodically rest or contract certain muscles. Your neurologist may ask you to change positions — for example, to bend your arm — during the test, depending on the muscles or nerves that they are trying to test at the time.
The needle electrodes will be removed after the test is over.
You may experience some temporary minor bruising where the needle electrode was put into your muscle. The bruising should heal within several days. If your bruising does not fade after a few days, contact your primary care doctor.
The neurologist will interpret the results of your exam and prepare a report. Your primary care doctor, or the doctor who ordered the EMG, will discuss the report with you at a follow-up appointment.