The UCSF Electromyography Clinic offers electromyography (EMG) testing, which assesses the health of your muscles and the nerves controlling those muscles. You may have an EMG if you are experiencing weakness or signs of impaired muscle strength. The test can help distinguish between muscle conditions and muscle weakness caused by neurologic disorders.
We also offer nerve conduction velocity (NCV) testing, which is often performed with an EMG. An NCV measures the speed of signals through a nerve and is used to diagnose nerve damage or destruction. Occasionally, the test may be used to evaluate nerve or muscle diseases, including myopathy, Lambert-Eaton syndrome and myasthenia gravis.
We are part of the UCSF Weill Institute for Neurosciences.
In most cases, no special preparation is necessary. Avoid using any creams or lotions on the day of the test. Risks are few, but you may experience some bleeding or infection at the electrode sites.
For an EMG, we insert a needle electrode through your skin into the muscle. The electrical activity detected by this electrode displays on a laboratory instrument called an oscilloscope and may be heard through a speaker.
After placement of the electrodes, you may be asked to contract the muscle – for example, by bending your arm. The presence, size and shape of the waveform shown on the oscilloscope provide information about the muscle's ability to respond when the nerves are stimulated.
You may feel some pain or discomfort when the electrodes are inserted, but most people are able to complete the test without significant difficulty. Afterward, the muscle may feel tender or bruised for a few days.
Tell your doctor if you have a cardiac defibrillator or pacemaker, as precautions may need to be taken. Otherwise, there are essentially no risks associated with NCV.
We place surface electrode patches – similar to those used for an electrocardiogram – on your skin over the nerve at various locations. Each electrode gives off a very mild electrical impulse, which stimulates the nerve. The other electrodes record the nerve's resulting electrical activity. The distance between electrodes and the time it takes for electrical impulses to travel between them allow us to determine the speed of nerve signals.
The impulse may feel like an electric shock and may be uncomfortable. You will feel it to varying degrees, depending on how strong the stimulus is. You should feel no pain once the test is finished.
Doctor referral required
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