Electromyography (EMG) and Nerve Conduction Velocity Tests (NCV)
Electromyography (EMG, myogram, or nerve conduction test) is a neurodiagnostic test used to assess the health and function of the muscles and the nerves that control the muscles. It can be used to determine whether muscle weakness and loss of muscle strength are caused by a muscle injury or by an underlying neurological disorder.
Nerve Conduction Velocity tests (often referred to as NCV tests or NCS, nerve conduction studies) are commonly performed during the course of an EMG test and provide additional valuable diagnostic information to the physician. This test evaluates nerves by measuring how fast the electrical impulse travels through them. Certain nerve diseases cause electrical signals to be transmitted more slowly than normal.
EMG/NCV tests can be used to detect many disorders and conditions, including the following:
Other nerve and muscle related injuries and disorders
There is no special preparation required for an EMG. Patients may be advised to avoid the use of creams and lotions on the day of the test.
When a muscle is at rest, it is electrically "silent." When a muscle is contracted, it generates a variety of signals known as “action potential.” An EMG measures this action potential.
During an EMG, a needle electrode is inserted through the skin into the muscle being tested and the patient is asked to contract the muscle in some way. The electrical activity produced during the test is displayed as waves on an oscilloscope, and may be heard on a speaker as loud pops. The presence, size, and shape of the waves indicate the ability of the muscle to respond to nerve stimulation and can help diagnose nerve or muscle damage.
The test normally takes 30 to 60 minutes to perform.
The NCV test procedure is normally conducted during the EMG testing. While a patient is resting on the exam table, several small recording wires are taped to the patients hand or foot. A small electric stimulator is placed on the skin close to the wires, and an electrical impulse is administered. The signal, after traveling down the nerve, is recorded by the electrode wires and printed on a graph.
During the test, there may be some discomfort when the needle is inserted into the muscle. Following an EMG, the area may feel tender or sore for a few days.
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