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Electromyography/Nerve Conduction Studies (EMG/NCS)

Doctors often order electrodiagnostic studies to diagnose different causes of arm or leg pain, numbness, and/or weakness. They are used when an imaging test such as an MRI does not adequately explain a patient’s symptoms or if the doctor suspects the patient has more than one health problem that could be causing the symptoms.

Electrodiagnostic studies can also help evaluate generalized nerve problems such as polyneuropathies, which can be caused by conditions such as diabetes. With spine problems, doctors often use these studies to further evaluate a pinched nerve in the neck or lower back (radiculopathy).

It takes about 25 to 30 minutes to study a single arm or leg. Your doctor will conduct a brief history and physical exam to identify the nerves and muscles that need to be further evaluated. The electromyography (EMG) portion of the nerve study only takes a few minutes. The rest of the time, your doctor will tape small electrodes over different muscles to evaluate individual nerves.

Once the electrodes are in place, the doctor will use a stimulator to deliver a small electrical impulse to the nerves that connect to the muscle. It feels like a small static electricity shock, and patients often describe the sensation as a “strong tap.”

For the EMG test, your doctor will insert a very small needle – approximately the size of an acupuncture needle – about 1/8” to 1/4” under the skin and into specific muscles. This portion is very short, taking only a minute or two. Your doctor can study approximately three to seven muscles at a time.

Your doctor will ask you to relax and then gently contract the muscle. Your doctor will evaluate the electrical wave forms recorded by the electrode. The EMG test is similar to an EKG study, where the electrode records the electrical signals generated by a muscle when it contracts. If there is damage to the nerve supplying the muscle, the doctor can easily see these abnormalities. The doctor can localize the nerve problem to a specific one in the back, or from a single nerve further down the limb (such as carpal tunnel syndrome).