An electromyogram (EMG) measures the electrical activity of muscles at rest and during contraction. Nerve conduction studies measure how well and how fast the nerves can send electrical signals. Nerves control the muscles in the body with electrical signals called impulses. These impulses make the muscles react in specific ways. Nerve and muscle problems cause the muscles to react in abnormal ways.
The nerve testing is performed by our certified electrodiagnostic clinical specialist. For electromyogram, the skin over the areas to be tested is cleaned. A needle electrode that is attached by wires to a recording machine is inserted into a muscle. When the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. Our electrodiagnostic clinical specialist asks you to tighten (contract) the muscle slowly and steadily. This electrical activity is recorded. The electrode may be moved a number of times to record the activity in different areas of the muscle or in different muscles.
The electrical activity in the muscle is shown as wavy and spiky lines on a video monitor and may also be heard on a loudspeaker as machine gun-like popping sounds when you contract the muscle. An EMG may take 30 to 60 minutes. When the test is done, the electrodes are removed and those areas of the skin where a needle was inserted are cleaned. You may be given pain medicine if any of the test areas are sore.
You may be a candidate for electrodiagnostic testing if you suffer from tingling, numbness, weakness, or pain that radiates from your spine or neck. Using electrodiagnostic testing, your doctor or therapist can evaluate the cause of symptoms and make a diagnosis. This helps eliminate confusion over whether muscle weakness is a result of pain or physical damage.
A nerve conduction velocity test (NCV) is an electrical test that is used to determine the adequacy of the conduction of the nerve impulse as it courses down a nerve. This test is used to detect signs of nerve injury. In this test, the nerve is electrically stimulated, and the electrical impulse ‘downstream’ from the stimulus is measured. This is usually done with surface patch electrodes (they are similar to those used for an electrocardiogram) that are placed on the skin over the nerve at various locations. One electrode stimulates the nerve with a very mild electrical impulse.
The resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission (nerve conduction velocity). A decreased speed of transmission indicates nerve disease. A nerve conduction velocity test is often done at the same time as an electromyogram (EMG) in order to exclude or detect muscle conditions.
During an EMG, a very fine, sterile needle will be inserted through the skin and into the muscle being examined. You may experience some discomfort, but it should not exceed that of an injection. You’ll be asked to gently flex the muscle while data is collected. The nerve conduction study is less invasive, using topical electrodes rather than needles. Electrical pulses will be sent between electrodes to determine how quickly the energy is transferred through the nerves. It usually takes about an hour to perform electrodiagnostic testing, which may consist of EMGs, nerve conduction studies, or both.
In most cases, you will receive the preliminary results of electrodiagnostic testing on the same day as the tests. Depending on those results, Dr. Vossoughi may be able to pinpoint the cause of your symptoms. Sometimes, the results of EMGs and nerve conduction studies are not definitive. However, they may provide diagnostic clues from which Dr. Vossoughi may determine your treatment.