Electromyography (EMG) is a diagnostic procedure that evaluates the health condition of muscles and the nerve cells that control them. These nerve cells are known as motor neurons. They transmit electrical signals that cause muscles to contract and relax. An EMG translates these signals into graphs or numbers, helping doctors to make a diagnosis.
A doctor will usually order an EMG when someone is showing symptoms of a muscle or nerve disorder. These symptoms may include tingling, numbness, or unexplained weakness in the limbs. EMG results can help the doctor diagnose muscle disorders, nerve disorders, and disorders affecting the connection between nerves and muscles.
There are two components to an EMG test: the nerve conduction study and needle EMG. The nerve conduction study is the first part of the procedure. It involves placing small sensors called surface electrodes on the skin to assess the ability of the motor neurons to send electrical signals. The second part of the EMG procedure, known as needle EMG, also uses sensors to evaluate electrical signals. The sensors are called needle electrodes, and they are directly inserted into muscle tissue to evaluate muscle activity when at rest and when contracted.
During each part of the EMG procedure, one electrode releases a very mild electrical signal while the other electrodes measure how long it takes for the signal to reach them. This mimics the natural electrical signals sent by the nerves to the muscles. The distance between the electrodes and time it takes for a signal to reach them is used to determine the speed at which the nerves are able to send and receive signals. An abnormal speed usually indicates a muscle or nerve disorder.
Some doctors may refer to electromyography as an electrodiagnostic exam.
Your doctor may perform an EMG if you’re experiencing symptoms that may indicate a muscle or nerve disorder. Some symptoms that may call for an EMG include:
- muscle weakness
- muscle pain or cramping
- involuntary muscle twitching (or tics)
The results of an EMG can help your doctor determine the underlying cause of these symptoms. Possible causes could include:
- muscle disorders, such as muscular dystrophy
- disorders that affect the ability of the motor neuron to send electrical signals to the muscle, such as myasthenia gravis
- peripheral nerve disorders that affect the nerves outside the spinal cord, such as carpal tunnel syndrome
- nerve disorders, such as amyotrophic lateral sclerosis (ALS)
Make sure to notify your doctor about any over-the-counter or prescription medications you may be taking. It’s also important to tell your doctor if you have a bleeding disorder, or if you have a pacemaker or implantable defibrillator. You may not be able to have an EMG if you have any of these medical conditions or devices.
If you are able to have an EMG, you should do the following beforehand:
- Avoid smoking for at least three hours before the procedure.
- Bathe or take a shower to remove any oils from the skin. Don’t apply any lotions or creams after washing.
- Wear comfortable clothing that doesn’t obstruct the area that your doctor will be evaluating. You may be asked to change into a hospital gown right before the procedure.
You will be asked to lie down on an examination table or to sit in a reclined chair. Your doctor may ask you to move into different positions during the procedure.
An EMG has two parts: the nerve conduction study and the needle EMG. The nerve conduction study is performed first. During this portion of the procedure, your doctor will apply several electrodes to the surface of your skin, usually in the area where you are experiencing symptoms. These electrodes will evaluate how well your motor neurons communicate with your muscles. Once the test is complete, the electrodes are removed from the skin.
After the nerve conduction study, your doctor will perform the needle EMG. Your doctor will first clean the affected area with an antiseptic. Then, they will use a needle to insert electrodes into your muscle tissue. You may feel slight discomfort or pain while the needle is being inserted.
The needle electrodes will evaluate the electrical activity of your muscles when contracted and when at rest. These electrodes will be removed after the test is over.
During both parts of the EMG procedure, the electrodes will deliver tiny electrical signals to your nerves. A computer will translate these signals into graphs or numerical values that can be interpreted by your doctor. The entire procedure should take between 30 and 60 minutes.
An EMG is a very low-risk exam. However, you may feel sore in the area that was tested. The soreness may last for a few days and can be relieved with an over-the-counter pain reliever, such as ibuprofen.
In rare cases, you may experience tingling, bruising, and swelling at the needle insertion sites. Make sure to tell your doctor if the swelling or pain becomes worse.
Your doctor may review the results with you right after the procedure. However, if another health care provider ordered the EMG, then you may not know the results until you attend a follow-up appointment with your doctor.
If your EMG shows any electrical activity in a resting muscle, then you may have:
- a muscle disorder
- a disorder affecting the nerves that connect to the muscle
- inflammation caused by an injury
If your EMG shows abnormal electrical activity when a muscle contracts, then you may have a herniated disc or a nerve disorder, such as ALS or carpal tunnel syndrome.
Depending on your results, your doctor will talk to you about any additional tests or treatments that might be needed.