Electromyogram (EMG) | ||
What is an electromyogram? EMGs can be used to detect abnormal muscle electrical activity that can occur in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), amyotrophic lateral sclerosis (ALS) (also known as Lou Gehrig disease), myasthenia gravis, disc herniation, and others. Why is an EMG test done? What kinds of EMG are there? Intramuscular EMG (the most commonly used type) involves inserting a needle electrode through the skin into the muscle whose electrical activity is to be measured. Surface EMG (SEMG) involves placing the electrodes on (not into) the skin overlying the muscle to detect the electrical activity of the muscle. Intramuscular EMG is the "classic" form of EMG (and is the main subject here). How is an intramuscular EMG done? Since skeletal muscles are often large, several needle electrodes may need to be placed at various locations to obtain an informative EMG. After placement of the electrode(s), the patient may be asked to contract the muscle (for example, to bend the leg). The presence, size, and shape of the wave form (the action potential) produced on the oscilloscope provide information about the ability of the muscle to respond to nervous stimulation. Each muscle fiber that contracts produces an action potential. The size of the muscle fiber affects the rate (how frequently an action potential occurs) and the size (the amplitude) of the action potential. How do you prepare for an intramuscular EMG? Does an EMG hurt? What is the current status of a surface EMG (SEMG)? The American Association of Electrodiagnostic Medicine has reported: "There is in fact almost no literature to support the use of SEMG in the clinical diagnosis and management of nerve or muscle disease." Still, the SEMG may prove of value in the future in helping to monitor the progression of disorders of the nerves and muscles. What other test is done during an intramuscular EMG? The NCV test can be used to detect true nerve disorders (such as neuropathy) or conditions whereby muscles are affected by nerve injury (such as carpal tunnel syndrome). Normal body temperature must be maintained for the NCV test, because low body temperatures slow nerve conduction. The word "electromyography" looks dauntingly long but it is made up of three parts: "electro-" + "-myo-" + "-graphy." ("-myo-" is from the Greek "mys", meaning muscle and "graphy" comes from the Greek "grapho" meaning to write) . So electromyography literally is the writing (recording) of muscle electricity. ¡@ cited from http://www.medicinenet.com/Electromyogram/article.htm ¡@ | ||