How is electromyography (EMG) used in the workup of cervical radiculopathy?

Updated: Oct 08, 2018
  • Author: Gerard A Malanga, MD; Chief Editor: Sherwin SW Ho, MD  more...
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  • Electromyography (EMG)

    • Electrodiagnostic studies are important in identifying physiologic abnormalities of the nerve root and in ruling out other neurologic causes for the athlete's complaints. EMG has been shown to be useful in the diagnosis of radiculopathy and has correlated well with findings on myelography and surgery.

    • EMG has 2 parts: (1) nerve conduction studies and (2) a needle-electrode examination. The nerve conduction studies are performed by placing surface electrodes over a muscle belly or sensory area and stimulating the nerve that supplies either the muscle or sensory area from fixed points along the nerve. From this, the amplitude, distal latency, and conduction velocity can be measured. The amplitude reflects the number of intact axons, whereas the distal latency and conduction velocity is more indicative of the degree of myelination.

    • The needle EMG portion of the electrodiagnostic examination involves inserting a fine-needle electrode into a muscle. Electrical activity is generated by the needle insertion into the muscle, voluntary muscle contraction, and the spontaneous firing of motor units. The activity is observed on an oscilloscope screen and quantified; an audible sound is also generated.

      • Denervated muscle produces spontaneous electrical activity while the muscle is at rest. These potentials are called fibrillations or positive sharp waves based on their characteristic shape and sound. Changes can be also seen in the configuration of the individual motor unit, as well as an increase in the firing rate of the individual motor units.

      • The timing of the EMG evaluation is important because positive sharp waves and fibrillation potentials first occur 18-21 days after the onset of a radiculopathy; therefore, it is best to delay this study until 3 weeks after an injury, to ensure that the results are as accurate as possible.

    • The primary use of EMG is to confirm nerve root dysfunction when the diagnosis is uncertain or to distinguish a cervical radiculopathy from other lesions when the physical examination findings are unclear. Although electrodiagnostic studies are very sensitive and specific, normal EMG results in a patient with signs and symptoms consistent with a cervical radiculopathy do not exclude the diagnosis of cervical radiculopathy.

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