Nerve Conduction Study and Electromyography
In the nerve conduction study (NCS) and electromyography (EMG) tests, nerves are stimulated to record responses from the muscles and to identify the status of the disease. These tests measure the electrical activity of muscles and the speed of the conduction of impulses through nerves. Measuring the electrical activity of muscles and nerves can determine whether muscle weakness is caused by a disease of the neurons, muscles, or neuromuscular junctions.
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If neuropathy is suspected, a nerve conduction study can determine
whether symptoms are caused by damage to the nerve fiber (axon) or
by disease of the insulating sheath (myelin) that surrounds the
nerve.
The selection of muscles and nerves to be tested is based on
neurological symptoms. A small thin, needle is inserted into
several muscles to measure electrical activity, and the nerve
response to a small electrical stimulation is recorded by a small
surface electrode. The speed of this electrical current is measured
as it moves down the nerve axon. The needle is moved within the
muscle to stimulate electrical activity in the muscle. The patient
is asked to contract the muscle while the needles are within the
muscle. No electrical stimulation is applied when studying the
muscle's electrical activity.
The physician observes and listens to the electrical signals from
the muscles transmitted to the EMG machine by the needle. The
signals are interpreted by the physician to establish a diagnosis.
The discomfort reported by patients having an EMG is comparable to
an intramuscular injection, although brief and less painful. Nerve
conduction studies may be slightly uncomfortable when the needle
goes through the skin and when the electrical stimulation is
applied. Some patients experience a tingling sensation and muscle
twitch when the electrical current is applied. Nerve conduction
studies are safe and usually well tolerated by most patients.
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