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Electrodiagnostic Testing

What is Electrodiagnostic Testing and Why is My Doctor Ordering This Test?

By  Dallin L. DeMordaunt, MD in “We’ve Got Your Back Magazine”

Electrodiagnostic Testing: What is it?

Electrodiagnostic testing includes a variety of tests that a doctor may request to examine the function of a patient’s muscles and nerves.  The most common electrodiagnostic tests are an electromyogram (EMG) and nerve conduction studies (NCS).  These tests are often done when a patient complains of neck or back pain associated with numbness, tingling, burning or pain radiating into the arms and legs. These tests also evaluate for other nerve or muscle abnormalities along the path of the nerve as it travels from the spine to the hands and feet such as carpal tunnel syndrome or neuropathy.

A nerve is very similar to an insulated wire commonly used in home electronics. If the insulation to the wire is damaged, it no longer conducts electricity as well.  Also if the wire itself is damaged, conduction is impaired.  A nerve is comprised of an axon, which is analogous to the wire and its sheath which is similar to a wire’s insulation.  If either of these are damaged, the nerve cannot transmit information to our body appropriately. When the nerve is injured, a patient may develop symptoms of numbness, tingling burning, weakness, and occasionally a change in bowel or bladder control.

When the nerve is injured at the spot where the nerve exits the spine, it is called a radiculopathy.  The nerve can be injured as it exits the spine usually in two ways: by being squeezed or by chemicals damaging the nerve.  The nerve can be squeezed if the canal or tunnel that the nerve travels through as it exits the spine is narrowed by arthritis or other medical problems.  This narrowing is called stenosis.  Also a nerve can be compressed by an injured disk in the spine. Disks act like shock absorbers for the spine and the nerves travel behind the disks.  When the disks are injured, they may push outward (a disk herniation) and compress the nerve that is traveling nearby.

Chemicals, released when the spine is injured, can also cause a radiculopathy. The chemicals irritate the nerve and can cause nerve damage.  When it is damaged, a nerve slows down, responds weakly, and poorly communicates with the muscles for which it is responsible.

How is electrodiagnostic testing done?

Electrodiagnostic testing typically consists of an electromyogram (EMG) and nerve conduction studies (NCS).  An EMG records normal and abnormal electrical activity in the muscles.  The examiner will test several muscles by inserting a small needle into the muscle which detects the electrical impulses.  The examiner will both see and hear these impulses on a screen and determine whether they are normal or not.  With nerve conduction studies (NCS), the nerve is electrically stimulated. Small recording pads (electrodes) are placed on the nerve or muscle in a different location than where it is stimulated.  The examiner measures the distance between these points and calculates the velocity and strength of the nerves response.   Most patients tolerate the tests without difficulty but do report some temporary discomfort during the testing procedure and may have some muscle soreness after the test.  A patient should notify the examiner prior to examination if they are on any blood thinning medications; have a pacemaker, defibrillator, or other implanted devices; have a blood transmitted illness; or have had recent fevers or symptoms of infection.  Do not apply creams or moisturizers to the skin on the day of the exam.

Who Performs Electrodiagnostic Testing?

Electrodiagnostic testing should only be performed by doctors specifically trained in this test.  The physicians at Sierra Regional Spine Institute are professionally trained and certified in electrodiagnostic testing and have years of experience. If you have concerns  about nerve or muscle function, please contact Sierra Regional Spine Institute for an expert evaluation.