Diagnosing Back Pain with An Electromyogram (EMG)

An electromyogram (EMG) is a diagnostic test that measures the electrical impulses emitted by muscles while resting and moving. The test involves the insertion of thin needles into the muscle. These needles act as electrodes and conduct electrical impulses to a machine called an electromyograph. The electromyograph records the information and generates the electromyogram report.

When nerve roots are compressed, the electrical impulses to the muscle served by that nerve begin to slow. This may lead to spontaneous contraction of the muscle or to impaired muscle function. An EMG can show when muscles are receiving impaired nerve signals due to compression disorders like a ruptured disc, bulging disc or spondylolisthesis.

Specifics of the dermatome map

Generally, EMGs do not require extensive preparation. Some things to discuss with your physician before taking an EMG include:

  • Medications – Muscle relaxants or anti-cramp medications may interfere with EMG accuracy. Ask your physician if you should stop taking these medications before the test and, if so, how far in advance to discontinue their use.
  • Blood Problems – Since there is a small risk of bleeding from the needle insertion site, you should talk to your physician if you have bleeding problems like hemophilia or if you take blood thinners.

What to expect during and after an EMG

During the test, you will be asked to sit or lie down on a table. The skin above the muscle(s) to be tested will be cleaned, and then small needles will be inserted through the skin into the muscle. The pain is usually less than the pain from an injection because the needles are not hollow, and there is no medication injected.

As soon as the needles are inserted, they begin measuring the electrical impulses of the muscle while it is at rest. The technician may ask you to contract the muscle, and the electrode will measure the electrical impulses during contraction. The needle(s) may be moved to different sites to measure different muscles or different areas of the same muscle. The test generally takes 30-60 minutes.

After the test, you’ll be allowed to go home. Some patients experience soreness in the muscles that were tested. If you have any pain, you may be prescribed pain relievers or directed to take over-the-counter analgesics. The EMG results will be sent to your doctor for study and analysis.