Electromyography
Electromyography (EMG) is a diagnostic procedure that can help assess the health of muscles and the nerve cells controlling them. This procedure can reveal muscle dysfunction, nerve dysfunction, or problems with nerve-to-muscle signal transmission.
Electrical signals are transmitted by motor neurons that cause the muscles to contract. An EMC uses small devices known as electrodes, in order to translate these signals into graphs, sounds, or numerical values that can be interpreted by a specialist.
Purpose
An EMG is generally ordered by your doctor, if you show signs or symptoms such as tingling, numbness, muscle pain or cramping, muscle weakness, or certain kinds of limb pain.
This procedure also helps to diagnose or rule out several conditions, which includes:
- Muscle disorders, like muscular dystrophy or polymyositis
- Disorders of the nerves outside your spinal cord (peripheral nerves), like peripheral neuropathies or carpal tunnel syndrome
- Diseases that affect the connection between the nerve and the muscle, such as myasthenia gravis
- Disorders affecting nerve root, such as a herniated disk in the spine
- Disorders that affect the motor neurons in your brain or your spinal cord, such as polio or amyotrophic lateral sclerosis
Preparation
Before your procedure, make sure you notify your doctor about any medications or supplements that you are taking. It is also important to inform your doctor if you have any bleeding disorder, or if you have an implantable defibrillator or a pacemaker. You might not be eligible for an EMG if you have any of these medical devices or certain conditions.
If you are considered eligible for the procedure, you need to remember to:
- Avoid smoking on the day of the procedure
- Wear comfortable clothing that will not obstruct the area that your doctor is going to evaluate. Sometimes you might also be asked to change into a hospital gown right before the procedure is performed.
- It is important to bathe or take a shower so that any oil from your skin is removed. Remember not to apply any lotions or creams afterward.
Procedure
It is likely that you will be able to change into a hospital gown for the procedure before you lie down on an examination table. In order to prepare for the study, the neurologist or a technician places surface electrodes at different locations of your skin depending on where you are experiencing symptoms. Depending on your symptoms, the neurologist may insert needle electrodes at different sites.
During the procedure, the surface electrodes will transmit a tiny electrical current which you may feel as a twinge or a spasm. The needle electrode might cause some pain or discomfort, though it will end shortly after the needle is removed.
During the needle EMG, the neurologist is going to assess whether there is any spontaneous electrical activity when the muscle is at rest, an activity that isn’t present in healthy muscle tissue, and the degree of activity when you contract the muscle slightly.
He/she will also give you instructions on resting and contracting your muscle at appropriate times. You might also need to change positions during the exam, depending on what muscles and nerves the neurologist is examining. If you are concerned about discomfort or pain at any time during the exam, you can talk to your neurologist about taking a small break.
Results
Right after the procedure, your doctor will be able to review the results with you.
If your EMG shows any electrical activity in a resting muscle, then you may have:
- a muscle disorder
- inflammation caused by an injury
- a disorder that affects the nerves that connect to the muscle
If your EMG is showing abnormal electrical activity when a muscle contracts, then you might be having a herniated disc or a nerve disorder, which can be as ALS or carpal tunnel syndrome.
Your doctor will discuss additional tests or treatments with you, depending on your results.
Risks
An EMG carries very low-risks. However, it might feel sore in the area that was tested. The soreness can last for a few days and it can be relieved with an over-the-counter pain reliever.
Sometimes, you might also experience tingling, bruising and swelling at the needle insertion sites. If your swelling or pain becomes worse, then make sure to tell your doctor.