Electromyogram or EMG is a test that helps diagnose a variety of disorders involving peripheral nerves, muscles and spinal nerves and symptoms including numbness or tingling, pain, muscle weakness, low back pain, sciatica, Carpal Tunnel syndrome or radiculopathy.
The test will take 30-45 minutes. There are two parts to the study: the nerve conduction studies and EMG needle study. Each part of the study gives information which will help to determine the functional quality of the peripheral nerves and muscles tested. This test may cause mild to moderate discomfort. A mild analgesic or ice may be used if there is discomfort. Occasional bruising may occur.
Needle electromyography (EMG) refers to the recording of muscle electrical activity using a thin pin electrode. The pin electrode is inserted through the skin into the muscle. During the insertion, the licensed practitoner determines the resistance of the muscle. The practioner also evaluates the electrical activity of the muscle both at rest and during contraction of the muscle. The pin electrode translates the amount and intensity of the electrical activity into waveforms displayed on a computer screen. The sounds of the electrical activity are also emitted and interpreted by the practitoner.
Therefore, the practitoner is not only using sight and touch, but also sound to determine the proper diagnosis. After the practitoner finishes examining one muscle, he or she analyzes all of the data - the waveform, the sounds, and the feel of the muscle - to determine if and which other muscles may need to be studied.
Nerve conduction velocity studies (NCVs) are used to test the speed of impulses through a nerve. To perform this study, surface electrodes are used to stimulate the nerve by placing electrodes on the skin at various locations over the nerve. One electrode stimulates the nerve with a mild electrical impulse and the resulting electrical activity is recorded by the other electrode. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine whether the nerve is functioning appropriately.