What is an EMG/NCV test?
EMG, or electromyogram is a test used to record the electrical activity of muscles. Active muscles produce an electrical current that is usually proportional to the level of muscle activity. Another name for an EMG is a myogram.
There are two types of EMG — the intramuscular EMG and the surface EMG. The intramuscular EMG is the test most commonly ordered and involves inserting a needle electrode through the skin into the muscle in question. Surface EMG (SEMG) involves placing the electrodes on top of the skin overlying the muscle to detect the electrical activity of the muscle.
EMGs can detect abnormal muscle electrical activity in many diseases and conditions, including inflammation of muscles, pinched nerves, damage to nerves in the arms and legs, disc herniation, and degenerative diseases such as muscular dystrophy, Lou Gehrig’s disease, Myesthenia gravis, among others. The EMG helps to distinguish between muscle conditions in which the problem begins in the muscle and muscle weakness due to nerve disorders.
We typically order EMGs when we want to find out if a patient’s pain is related to a pinched nerve or disc herniation most commonly. Most pain conditions that we see are related to soft tissue injuries such as injuries to the ligaments, tendons, or muscles which do not require EMG testing. These injuries may refer pain down the arm or leg or to other sites. Almost all pain, in our experience, responds well to therapy (at least 85% of all cases seen here). If a patient has a pinched nerve, this person can be experiencing 10/10 level of pain, 24 hours per day, 7 days per week. The patient may experience true numbness, weakness, and decreased grip strength, for example. An EMG in this case helps determine cases of radiculopathy or pinched nerves.
In the nerve conduction velocity (NCV) test, the nerve is electrically stimulated by one electrode while other electrodes detect the electrical impulse “down stream” from the first electrode. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission (the nerve conduction velocity, or NCV). A decreased speed of nerve conduction indicates nerve disease.
The NCV test is often done at the same time as the EMG in order to exclude or detect both nerve and muscle conditions. The interpretation of an abnormal NCV test depends on why the test was done in the first place. It may indicate damage to a nerve from trauma, diabetic or peripheral neuropathy, herniated discs, polyneuropathy, or myasthenia gravis or Guillain-Barre Syndrome, among other things.
We take a very thorough history on each and every patient, as this is the key to determining the root cause of a patient’s pain. EMG/NCV tests are not something that we frequently order considering the number of pain patients who come through our doors, because we find that most conditions respond very well to therapy. Degenerative disc disease, arthritis, bulging discs, spondylolisthesis, and many other conditions are most typically due to an underlying soft tissue weakness/injury – to the ligaments, tendons, or muscles. These types of conditions respond very well to therapy. The history from the patient is one of the key factors to determining the need for these types of studies. The experience of the physician and clinical team at asking the right questions, can be the difference between getting an expensive test that you may or may not need. If a nerve injury is suspected as being the cause of the patient’s pain, then an EMG/NCV study may be ordered.
Visit us at All Injury Rehab for more information and to set up an appointment.