EMG/NCV
Electromyography (EMG) is a diagnostic procedure that evaluates the health condition of muscles and the nerve cells that control them. EMG results can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission.
A nerve conduction study (NCV), another part of an EMG, uses electrode stickers applied to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points.
Why is an EMG/NCV done?
PRI medical staff may order an EMG if you have signs or symptoms that may indicate a nerve or muscle disorder. Such symptoms may include:
- Tingling
- Numbness
- Muscle weakness
- Muscle pain or cramping
- Certain types of limb pain
EMG results are often necessary to help diagnose or rule out a number of conditions such as:
- Muscle disorders, such as muscular dystrophy or polymyositis
- Diseases affecting the connection between the nerve and the muscle, such as myasthenia gravis
- Disorders of nerves outside the spinal cord (peripheral nerves), such as carpal tunnel syndrome or peripheral neuropathies
- Disorders that affect the motor neurons in the brain or spinal cord, such as amyotrophic lateral sclerosis or polio
- Disorders that affect the nerve root, such as a herniated disk in the spine
What happens during an EMG?
You will be asked to lie down on an examination table. The doctor may ask you to move into different positions during the procedure.
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’re directly inserted into muscle tissue to evaluate muscle activity when at rest and when contracted.
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’re 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.
How do I prepare for an EMG?
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’re 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.
Common Conditions for EMG testing
Sciatica
Migraines
Neuropathy
Spinal Stenosis
Trauma/Injury
Lesion