An EMG, used in conjunction with a neurological examination, helps establish a diagnosis and the extent of a problem by measuring the electrical activity of a muscle in response to stimulation. 

An EMG is done by inserting electrodes in fine needles into the muscles being tested, and by placing electrodes on the skin over peripheral nerves. 

  • The presence, size, and shape of the wave form produced on the oscilloscope (the action potential) provide information about the ability of the muscle to respond to nervous stimulation.
  • Each muscle fiber that contracts will produce an action potential and the size of the muscle fiber affects the rate (how frequently an action potential occurs) and size (amplitude) of the action potential(s).

An EMG may be used to evaluate a variety of problems, including the following: 

  • Nerve damage from compression by a disk in the neck or the back
  • Nerve compression from carpal tunnel syndrome
  • Neuromuscular diseases such as amyotrophic lateral sclerosis (ALS), poliomyelitis, myasthenia gravis and muscular dystrophy
  • Peripheral neuropathy caused by such conditions as diabetes, pernicious anemia and heavy metal toxicity

In many instances, an EMG can provide critical diagnostic information that can not be obtained in any other way. 

Although there is some discomfort associated with the procedure, an EMG is usually done on an outpatient basis. 

Preparation:

 

No special preparation is usually necessary.

Procedure:

  1. The electrical activity detected by this electrode is displayed on an oscilloscope.
  2. You may be asked to contract the muscle.
  3. To perform intramuscular EMG, a needle electrode is inserted through the skin into the muscle tissue. A trained medical professional observes the electrical activity while inserting the electrode.

How It Feels:

  • Afterward, the examined muscle may feel tender or bruised.
  • Some discomfort may be felt with insertion of the electrodes.