EMG, Nerve Conduction Velocity, and SSEP
The three most common electrodiagnostic studies are electromyography (EMG), nerve conduction velocity studies (NCVs), and somatosensory evoked potential studies (SSEPs). Electromyography (EMG) and nerve conduction studies (NCV's) are often done at the same time.
Electromyography measures muscular response to electric stimulation in the nervous system. Needle electrodes are inserted through the skin into various muscles or muscle groups. The electrodes then record electrical signals from the muscles. These results measure the ability of the muscle to respond when nerves are stimulated, and help to pinpoint damaged nerves.
During an EMG, you may be asked to contract the muscles by bending your arm or leg. You may experience some discomfort from the insertion of the electrode needles. After the tests, your muscles may feel sore for a day or two. The risks to EMG are minimal, but include bleeding or infection at the site of needle insertion.
Nerve Conduction Velocity
A nerve conduction velocity study measures the ability of a nerve to transmit electrical impulses. During the NCV test, electrodes similar to EKG patches are placed on the skin along the path of the nerve. The nerve is stimulated by a low electrical impulse, and the electrodes assess the speed at which the electric current is transmitted. A damaged nerve will not transmit the electric impulse as well as a healthy nerve.
The test must be done at normal body temperature. During the test, you may feel the electric impulse as an electric shock. This may be uncomfortable for some patients. However, it is unusual to experience significant pain or discomfort from the test. There are no risks associated with NCV.
In a somatosensory evoked potential study, a nerve is stimulated by an electrical impulse. The transmission of that impulse along the spinal cord to the brain is then monitored via electrodes on the scalp. The SSEP study can be helpful when a patient shows signs of neurological damage.
Electrodiagnostic tests can help your surgeon assess your spinal condition by identifying muscle weakness and nerve damage caused by nerve related disorders. These tests are typically done in combination with other tests that your physician thinks might be helpful in evaluating your spine condition. Electrodiagnostic tests can also be used during major spine surgery to help make sure that nerves are not injured or damaged during the surgery.