What is electromyography?
Electromyography (EMG) is a diagnostic procedure that evaluates the health of the muscles and the nerve cells that control them. These nerve cells are called motor neurons. These transmit electrical signals that cause muscles to contract and relax. An EMG translates these signals into graphs or numbers, which helps doctors make a diagnosis.
An EMG is often prescribed by a doctor when someone shows signs of a muscle or nerve disorder. These symptoms can include tingling, numbness, or unexplained weakness in the limbs. EMG results can help the doctor diagnose the disorders of the muscle and neurological connection between nerves and muscles.
Some doctors may prescribe electromyography as an electrodiagnostic test.
Types of electromyography
There are two types of EMG: Superficial EMG and intramuscular EMG. Surface EMG assesses muscle function by recording surface muscle activity on muscle on the skin. Surface electrodes can only provide a limited estimate of muscle activity.
Purpose of electromyography
If a nerve or muscle disorder is doubted, the doctor may suggest electromyography. These symptoms can include:
- Muscular weakness
- Muscle pain
- Some types of organ pain
Electromyography results are often necessary to confirm or rule out several conditions:
- Muscle disorders, muscular dystrophy, or polymyositis
- Diseases that interrupt the function of the nerve and the muscle, such as myasthenia gravis
- Nerve disorders outside the spinal cord (peripheral nerves) such as carpal tunnel syndrome or peripheral neuropathy
- Disorders affecting motor neurons in the brain or spinal cord, amyotrophic lateral sclerosis, or polio
- Defects that affect the nerve root, such as a herniated disc in the spine
Before the electromyography
- Your doctor will explain the procedure to you and welcomes any questions on the same.
- Generally, fasting is not required before the test. In some cases, cigarettes and caffeinated beverages like coffee, tea, and cola are restricted before the test.
- Tell your doctor about all the medicines you are taking (prescription and over-the-counter) and herbal medicines.
- Tell your doctor if you have a pacemaker.
- Wear clothing that allows access to the area to be examined or easily removed.
- Avoid using lotions or oils on your skin for a few days before your procedure or the day of the test.
- Depending on your medical condition, your doctor may request specific preparation for others.
During the electromyography
The electromyography can be performed on a patient basis or as part of your hospital stay. The steps may vary depending on your health problem and the practices of your healthcare provider. Talk to your healthcare provider about what to do during your exam.
EMG is performed by a healthcare provider who specializes in neurological disorders. This is usually a neurologist or physical therapist. EMG often occurs after a neural conduction study.
Generally, electromyography tests follow this procedure:
You will be asked to remove clothing, jewellery, hairpins, glasses, headphones, or other metal objects that may interfere with the test.
- You will be given a gown to wear before the test.
- Your position is adjusted before the test.
- A neurologist finds the muscles that need to be studied.
- The skin is cleaned with an antiseptic solution. Next, a clean, fine needle is inserted into the muscle. A metal plate is placed under you.
- Multiple needles may be required to perform the test. You may feel some pain when placing the electrode. But it is often painless.
- If the test is painful, tell the examiner as it may lead to complications.
- You will be asked to relax and then do some full-strength muscle contractions.
- The electrical activity of the working muscles is measured and displayed on the monitor. An audio amplifier can also be used to check the appearance and sound of electrical power. If the recorder is connected to an audio amplifier, you may hear a snowflake on the tin roof as you contract your muscles.
After the electromyography
After testing, the electrodes are removed. You may be given pain relievers. Warm compresses can be placed on the affected area immediately after the test.
Some muscle aches last a day or more after the test. Tell your healthcare provider if you have any symptoms at the injection sites:
- Increased pain
Your healthcare provider may give you other instructions after the test based on your specific situation.
Risks factors of electromyography
Both EMG and NCS are low risk. With EMG, there is a risk of infection or bleeding where the electrodes are inserted. If you are taking anticoagulants (blood thinners) or have hemophilia, inform the neurologist who performs this procedure in advance. A disorder that prevents blood from clotting.
If you are testing the chest muscles with EMG, there is a small risk of air entering the space between the chest wall and the lungs, causing pneumothorax (lung collapse).
If you have NCS, tell your neurologist ahead of time if you have a pacemaker or cardiac defibrillator because you are about to receive mild electrical shocks. Care must be taken in this case.
Results of electromyography
Your doctor can review the results with you after the procedure. However, if another healthcare provider requests an EMG, you may not know the results until you schedule your next appointment with your doctor.
If your EMG shows any electrical activity in your muscles at rest, you may have:
- Muscle disorder
- A disorder that affects the nerves that connect to the muscle.
- Inflammation from injury
- If your EMG shows abnormal electrical activity during muscle contraction, you may have a neurological disorder such as a herniated disc or ALS, or carpal tunnel syndrome.
Depending on your results, your doctor may discuss additional tests or treatments with you.