Mount Auburn Healthcare Connection

Learn More:

• Related Links
• Quiz

The EMG (electromyogram) is a diagnostic procedure for measuring the electrical impulses of muscles. Similar to the EEG (electroencephalogram), which measures electrical impulses of the brain, and the EKG (electrocardiogram), which measures electrical impulses of the heart, the EMG allows physicians to see what is happening in the body’s nerves.

“When there’s evidence that a muscle, peripheral nerve or nerve root is damaged, a patient may be referred for an EMG,” explains Edward Wolpow, M.D., Neurologist at Mount Auburn Hospital in Cambridge, a teaching hospital of Harvard Medical School. It is common for a patient to be referred by an orthopedist, neurologist, neurosurgeon or pain specialist.

The EMG has been in use at Mount Auburn Hospital for more than 30 years. It is regularly used to diagnose carpel tunnel syndrome, which affects the median nerve at the wrist. At Mount Auburn Hospital, the procedure is also used to diagnose muscle and nerve damage caused by injured discs in the lower back or neck, as well as various forms of muscular dystrophy.

“When we suspect a nerve is damaged, this test shows if electrical impulses to muscles are endangered and to what extent,” says Dr. Wolpow. “This information, along with the degree of pain, helps us decide whether surgery is necessary.”

During the EMG, a very thin needle (thinner than those used for drawing blood) is inserted into a patient’s muscle. The needle is then hooked up to a monitor, which records the muscle’s electrical activity as the patient contracts and relaxes the specified muscles. “This is usually less painful than a flu shot because we only insert a needle; we don’t inject anything into the muscle, and no shock is administered,” says Dr. Wolpow. “We are able to see certain diseases electrically when monitoring a muscle that’s in trouble.”

The EMG is a two-part procedure. It is performed in tandem with nerve conduction tests, which are brief electric shocks delivered to the nerves. “This stimulation test allows us to record the speed and amount of electricity nerves are conducting,” says Dr. Wolpow. “It shows us if electricity is blocked or too slow.”

The nerve conduction test is performed on the skin over the nerve and is not invasive. During the test, very brief electrical shocks are delivered to the nerves at several different points along its course. “This may sound scary,” says Dr. Wolpow. “But patients feel more of a tapping sensation than pain. However, they may notice a jump in their fingers or feet.” On the monitor, the nerves appear as if they were little wires. Doctors are able to measure how quickly the nerves conduct electricity and determine if there are any blockages.

The EMG provides information specifically about the electrical activity in the muscles, while nerve conduction tests focus only on the nerves. “Since physicians are often concerned about the whole system, the nerves and the muscles they go to, it’s helpful to receive all this information at once,” explains Dr. Wolpow. “The nerve conduction test and EMG not only pinpoint where a problem is, but also help quantify the amount of damage.”

Patients do not have to undergo any special preparations for the EMG and nerve conduction tests; they can even be on pain relievers. The tests take up to about 30 minutes and do not require any recovery time.

For a free Mount Auburn Hospital physician directory, please call us at 617-499-5094.