Electromyography (EMG) is a diagnostic tool that evaluates muscle or nerve problems. It uses surface electrodes to assess the ability of motor neurons (the nerve cells that control your muscles) to transmit electrical signals. It also uses needle electrodes to evaluate your muscle activity when at rest and when contracted.
Electromyography may also be referred to as an electrodiagnostic exam.
According to Cedars-Sinai, an EMG is a useful way to find the cause, or causes, of certain symptoms (Cedars-Sinai). Some symptoms that may call for an EMG include:
- muscle weakness
- muscle pain or cramping
- involuntary muscle twitching
Conditions that may cause these symptoms could include:
- muscle disorders (such as muscular dystrophy)
- disorders affecting the ability of the motor neuron to communicate to the muscle (such as myasthenia gravis)
- peripheral nerve disorders (such as carpal tunnel syndrome), which affect nerves outside the spinal cord
- nerve disorders like amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease)
If you have a pacemaker or implantable defibrillator, or if you suffer from a bleeding disorder or lymphedema, you may not be able to have an EMG.
It’s also important to talk to your doctor before the test if you are taking blood thinners or any other medications, or if you have other medical conditions.
If you are able to have an EMG, you should do the following beforehand:
- Don’t smoke for at least three hours before the exam.
- Bathe or take a shower to remove any oils from the skin and don’t apply any lotions or creams after washing.
- Wear comfortable clothing that does not obstruct the area that your doctor will test. You may also be asked to change into a gown.
Recently, healthcare providers other than licensed physicians have been asking for the right to perform EMGs.
However, the American Academy of Neurology (AAN) has issued an advocacy statement saying that only physicians should perform intrusive, complex and intrinsically diagnostic tests such as EMGs (AAN).
According to the AAN, EMGs are highly dependent upon the observations of the person conducting the test. To reduce the risk of misdiagnosis, only physicians trained in neuromuscular conditions should conduct an EMG.
The EMG usually has two parts:
- a nerve conduction study, which uses electrodes taped to your skin to evaluate your motor neurons
- a needle electrode exam, which uses a small needle inserted into your muscles to evaluate your muscles’ electrical activity
During the EMG, you will lie down on an exam table or recline comfortably in a chair. Your doctor may ask you to move into different positions during the exam.
Some patients report pain and discomfort during an EMG. If at any point the test becomes too painful, you can ask your doctor to take a break.
The entire procedure should take between 30 and 60 minutes.
Nerve Conduction Study
During this part of the procedure, your doctor will apply several small electrodes to the surface of your skin. This will evaluate how well your motor neurons communicate with your muscles. The electrodes will deliver electrical stimuli to your nerves, and the information is transferred to a small computer as waveforms.
You may feel a tingling or twitching sensation during this portion of the test. Once the test is complete, the electrodes are removed.
Needle Electrode Exam
Next, your doctor will sterilize specific parts of your body and insert a small, thin needle. You may feel slight discomfort or pain while the needle is being inserted.
The needle electrodes evaluate electrical activity in your muscles, both when at rest and when contracted. The computer translates this electrical activity visually as waveforms and audibly as popping sounds.
Once the test is complete, the needle electrode is removed.
An EMG is a low-risk exam. Some patients may feel soreness in the areas being tested. This may last for a few days and can be relieved with an over-the-counter pain reliever.
Some patients also report tingling, bruising and swelling at the needle insertion sites. While the risk of infection is low, you should tell your doctor if the swelling or the pain grows worse.
Your doctor may immediately review the results of the test with you. Or, if another physician ordered the test, you may review the results at a follow-up visit.
At that time, your doctor will also talk to you about any additional tests or treatments that might be needed.