Electro-diagnostic Studies (EMG/NCS)
Nerves use electrical impulses to coordinate muscle movement in our bodies. Diseases affecting the muscles and nerves can result in abnormal electrical activity.
Electromyography (EMG) and Nerve conduction studies are diagnostic tests used to detect nerve and muscle disorders and to evaluate the functioning of your nerves and muscles. An EMG is designed to record the electrical activity produced by the muscles, during rest and contraction. Nerve conduction studies measure the conductivity of the nerves.
Your doctor may arrive at a diagnosis based on the results of the EMG along with information from your medical history, physical and neurological examinations, and results from other tests.
EMG testing can be used for the diagnosis of a variety of disorders that damage muscle tissue, nerves, or the junctions between nerve and muscle such as a herniated disc, amyotrophic lateral sclerosis (ALS), or myasthenia gravis (MG). An EMG can also be used to evaluate the cause of weakness, paralysis, and muscle twitching.
Nerve Conduction Studies (NCS) are used to detect damage or injury to the peripheral nervous system (PNS), which consists of the extracranial nerves and spinal cord. This test can be used to diagnose neurological disorders, such as carpal tunnel syndrome or Guillain-Barré syndrome.
Before the procedure
Certain medications that act on the nervous system can cause abnormal test results. Therefore, your physician may advise you to stop these medicines 3 to 6 days prior to your procedure. If you are on blood thinners, your doctor may ask you to stop taking them, before the test. Also, inform your doctor if you have a pacemaker implanted. You will be instructed not to smoke, eat or drink foods that contain caffeine for 3 hours before the test.
Electromyography is performed by an EMG technologist or a doctor. It may be conducted in a doctor's office, hospital or clinic. During the test, you will be asked to sit on a reclining chair or lie down on a table or bed so that the muscles being tested are relaxed.
Electromyography: An EMG normally takes about 30 to 60 minutes. The skin over the test site is cleansed and a needle electrode is inserted into the muscle, connected by wires to a recording machine. You may feel a quick, sharp pain during the insertion of the electrode. The doctor then records your readings with the muscle at rest and under contraction. The needle electrode may be moved several times to record the electrical activity in different areas of the muscle. On the computer screen the electrical activity may be depicted as wavy and spiky lines. Electrical impulses may also be monitored through a speaker, in which the electrical signals are denoted by a popping sound or monitored on video. After the test, the needle electrode is removed and your skin is cleansed. Pain medications are given if you experience any soreness at the site of needle insertion.
Nerve conduction studies: A nerve conduction study usually takes about 15 to 60 minutes depending on the number of areas to be studied. Often, nerve conduction studies are done before an electromyography (EMG). This test is usually done with several flat metal disc electrodes that are placed on the skin with a paste or tape. Your doctor places a shock-emitting electrode directly over the nerve to be studied and a recording electrode over the muscles supplied by that nerve. Small and brief electrical impulses are generated to stimulate the nerves. The time taken for the muscle to contract in response to the pulse is then recorded. The speed of transmission of the impulse is called nerve conduction velocity. To compare the conduction velocity, the corresponding nerves on the other side of the body may be studied. After the test, the electrodes are removed.
Some soreness and a tingling sensation may persist for 1 or 2 hours after electromyography. Call your doctor, if you experience increasing pain, swelling, tenderness or pus at any of the needle insertion sites.
In a nerve conduction study, the chance of any risks or complications is minimal as the amount of electricity that is transmitted is very small. You may experience a brief, burning pain, a tingling sensation and a twitching of the muscle during the transmission of the electrical impulses.
Certain factors or conditions may interfere with the test results. These tests are usually avoided in individuals with swelling, bleeding, or obesity and those taking medications, such as skeletal muscle relaxants and anticholinergics.