Electromyography (EMG) and Nerve Conduction Study (NCS)
What are they?
Electromyography (EMG) and nerve conduction studies (NCS) are two tests used to help diagnose nerve and muscle disorders. Although they are sometimes ordered independent of each other, they are often ordered together to be done in the same appointment. You can normally expect to complete both during your appointment.
• EMG measures electrical impulses in the muscles.
• Nerve conduction studies measure the speed and intensity of electrical signals that travel along the nerves, and the time it takes muscles to respond to these signals.
When are these tests helpful?
They are often used when a patient has symptoms such as muscle weakness, numbness, spasms, paralysis or pain.
A nerve conduction study is used to help evaluate or diagnose:
• Carpal tunnel syndrome and other mononeuropathies of the extremities
• Focal numbness and weakness
• Peripheral polyneuropathies
• Generalized weakness
• Myasthenia gravis
An EMG is used to help evaluate or diagnose:
• Muscle diseases
• Amyotrophic lateral sclerosis (Lou Gehrig’s disease)
• Nerve compression in the neck, back or extremities
• Peripheral polyneuropathies
• Disorders of neuromuscular transmission
• Cervical and lumbar radiculopathies
• Generalized weakness
• Focal weakness
Why are these tests helpful?
Nerves send electrical signals to muscles, cueing them to contract or relax, and muscles produce electrical activity when they move. When injury or disease affects nerves or muscles, the electrical activity changes. Electromyography and nerve conduction studies show those changes and help your physician make a diagnosis and determine treatment options.
How is a nerve conduction study performed?
In nerve conduction studies, stimulating electrodes are held against your skin. No needles are used. A tiny impulse is sent through your nerves and the responses are recorded. This test may be done by either our experienced EMG technician or the same doctor who will conduct the EMG.
This current is harmless and lasts 0.1 to 0.2 milliseconds. You may feel a tingling, or your muscles, fingers or toes might twitch.
Usually, the test takes about an hour and is done on an outpatient basis. You can resume normal activities once the nerve conduction study is completed.
How is an EMG conducted?
In EMG, the health care provider gently inserts a thin needle electrode into each muscle to be studied. You may feel a brief pain as the electrode is inserted, but because of its small size and because nothing is inserted through the electrode, the pain is less than a typical hypodermic injection. Most people tolerate the minor discomfort quite well.
A fine wire connects the electrodes to an electronic instrument that measures electric currents in the muscle. You’ll be asked to slowly flex muscles so the electrical activity can be measured.
Usually, the test takes about a half hour and is done on an outpatient basis. You can resume normal activities once the EMG is completed.
Who conducts these tests?
A board-certified neurologist typically conducts these tests and interprets the results. Some neurologists are board certified in electromyography, indicating advanced training in the field. In some appointments, a qualified EMG technician will conduct the first nerve conduction study portion of the testing, while a neurologist will always conduct the EMG.
The specialized neurologist also interprets the results, which requires analysis of the data transmitted to the computer and listening to the electrical impulses during the tests. Results are forwarded to your physician.