Electromyography, or EMG, is a test that is performed to diagnose neuromuscular disorders (medical conditions that affect the nerves and muscles).
An EMG records the electrical signals that travel from the spinal cord to the muscles in the arms and legs. It may be performed for people experiencing certain symptoms, such as the following:
- Muscle weakness
- Muscle pain or cramping
An EMG is frequently used to diagnose a variety of neurological conditions, including:
- 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 a herniated disk in the spine
How is an EMG performed?
During an EMG, very fine wire electrodes are inserted into a muscle. The electrodes are attached through a series of wires to a recording instrument.
Testing usually takes place at a testing facility and lasts about an hour but may take longer, depending on the number of muscles and nerves to be tested. Most patients find this test to be somewhat uncomfortable.
An EMG is usually done in conjunction with a nerve conduction velocity test (NCV), which measures electrical energy by assessing the nerve’s ability to send a signal. This two-part test is conducted most often in a hospital.
A technician tapes two sets of flat electrodes on the skin over the muscles. The first set of electrodes is used to send small pulses of electricity (similar to the sensation of static electricity) to stimulate the nerve that directs a particular muscle. The second set of electrodes transmits the responding electrical signal to a recording machine. The physician then reviews the response to verify any nerve damage or muscle disease.
Patients who are preparing to take an EMG or NCV test may be asked to avoid caffeine and not smoke for 2 to 3 hours prior to the test, as well as to avoid aspirin and non-steroidal anti-inflammatory drugs for 24 hours before the EMG. There is no discomfort or risk associated with this test.
Reference: The National Institute of Neurological Disorders and Stroke