It's electric—understanding electrodiagnostic testing
Richard L. Pullen EdD, MSN, RN, CMSRN

Nursing Made Incredibly Easy!
June 2014 
Volume 12  Number 3
Pages 12 - 15
  PDF Version Available!

The term electrodiagnostic testing is used to describe two specialized tests: electromyography (EMG) and nerve conduction studies (NCS). EMG and NCS are valuable diagnostic tools to evaluate pathology of the peripheral nervous system that may be a manifestation of a primary neurologic disorder or secondary to systemic disease. Sensory, motor, and autonomic signs and symptoms can be an initial finding of peripheral nervous system dysfunction.Often performed at the same time, EMG and NCS are useful to evaluate unexplained weakness, twitching, paralysis, numbness, tingling, or pain and can differentiate between types of peripheral neuropathy, inflammatory myopathy, neuromuscular disorders, and radiculopathy (see Selected conditions warranting EMG and NCS). A computed tomography scan, magnetic resonance imaging (MRI), and lab data may be used with electrodiagnostic testing to evaluate the etiology of the patient's signs and symptoms.Let's take a closer look at these two diagnostic tests.One type of EMG is called a surface EMG, in which electrodes are placed on the skin to determine muscle activity in particular positions or actions. The electrical activity of individual muscles or muscle groups is detected, amplified, and analyzed by a computer. The surface EMG is helpful in determining whether muscles, especially those located closer to the surface of the skin, are being used during exertion.A needle EMG is obtained by inserting a tiny needle attached to electrodes into the skeletal muscles to determine whether there's damage to nerve fibers of individual muscles. Shown on an oscilloscope, the electrical activity (electrical potential) of muscles is measured at rest and during contraction. Insertion activity, resting activity, and recruitment are among the findings that are evaluated via a needle EMG.A normal muscle is electrically silent when recorded from a needle electrode. Movement of the needle normally elicits a brief burst of electrical activity called insertion

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