Electro Diagnostic Studies (EMG)
Electromyography (EMG) is a diagnostic tool used to evaluate the health of muscles and the nerve cells that control them. These groups of nerves are known as motor neurons and they transmit electrical signals that cause muscles to contract. EMGs can study the electrical activity of muscle fibers individually and collectively. As an EMG records the communication between these nerves and their muscles it translates signals into graphs, sounds or numerical values that are then interpreted by a trained physician.
EMGs are often ordered when some sort of neuromuscular disorder is suspected. Symptoms that typically warrant an EMG include tingling, numbness, muscle weakness, muscle pain/cramping or other types of limb pain. EMGs help reveal dysfunctional nerves, muscles or problems in the communication between the two. Conditions that can be ruled out or diagnosed by EMGs include muscle disorders, such as muscular dystrophy or polymyositis; diseases that affect 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 polio; and disorders that affect the nerve root, such as a herniated disk in the spine.
EMGs use tiny devices called electrodes to transmit or detect electrical signals sent by motor neurons. Electrical activity is recorded by either surface or needle electrodes. Needle electrodes are used far more commonly in the clinical setting, and are evaluated during needle insertion, during periods of rest (spontaneous activity), and during periods of voluntary muscle contraction. During the EMG, a tiny needle electrode is inserted directly into a muscle and records the electrical activity in that muscle. An EMG can also be combined with a nerve conduction study. Nerve conduction studies use electrodes taped to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points.
Once completed the readings are interpreted by a specialist, usually a neurologist. When analyzing the results, the findings are looked at as a whole and the clinical symptoms are taken into accounts to help identify a disease pattern if one exists. No single abnormality on an EMG is solely diagnostic of a single disease process. The EMG is only an extension of the clinical investigation and must be interpreted in the proper clinical context.