An "EMG" examination has two parts, the electromyogram study and the nerve conduction studies. Together, these procedures measure the functional integrity of nerves and the muscles they supply. Images of nerves and muscles, such as MRI, cannot show if the nerve is functioning properly or not.
The electromyographic (EMG) study measures the electrical impulses of muscles at rest and during contraction by inserting a fine needle electrode into the muscle. Nerve conduction studies determine how well individual nerves can transmit electrical signals. Nerves control the muscles in the body using electrical impulses, and these impulses make the muscles react in specific ways. Nerve and muscle disorders cause the muscles to react in abnormal ways. Measuring the electrical activity in muscles and nerves can help detect the presence, location, and extent of diseases that can damage muscle tissue or nerves. In the case of nerve injury, the actual site of nerve damage can often be located. EMG and nerve conduction studies are usually done together to provide more complete information. The muscle's electrical activity is displayed on an oscilloscope and heard through a speaker. The presence, size, and shape of the wave form produced on the oscilloscope provide information about the ability of the muscle to respond when the nerves are stimulated.
The second part of the test is a set of nerve conduction studies. Nerves transmit information by electrical impulses. Thus, to test a nerve's health, a brief, mild electrical stimulus is applied to the nerve. This electrical impulse may feel like a brief, mild electric shock. Although it may be uncomfortable during the test, there should be no discomfort following the test's completion. This stimulus produces a diagram and from which measurements can be obtained. The nerve is stimulated, usually with surface electrodes, which are patch-like electrodes (similar to those used for ECG) placed on the skin over the nerve at various locations. The resulting electrical activity is recorded by the other electrodes.
