What is the role electrodiagnostic testing in an acute injury?

Updated: Jan 27, 2020
  • Author: Adam B Agranoff, MD; Chief Editor: Stephen Kishner, MD, MHA  more...
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A frequent misconception is that electrodiagnostic testing is not useful in an acute injury. Immediately following complete nerve transection, a complete loss of motor unit recruitment is noted distally (neurotmesis). Even with incomplete nerve injuries (neurapraxia and axonotmesis), decreased motor unit action potential recruitment patterns may be seen acutely.

Within the first 2-3 days, a decrease in motor amplitudes proximally may be noted. Sensory amplitude reductions are noted toward the end of the first week following injury. Slowing of conduction velocity across the site of injury suggests a demyelinating injury. Membrane instability can be detected by needle examination in 1-4 weeks, with proximal muscles showing up the soonest (due to Wallerian degeneration). At 2-6 months, axonal sprouting occurs, which results in increased motor unit action-potential amplitude and prolonged duration.

In a traumatic nerve injury or acute neuropathic process, serial EMG is often performed to assess disease progression or response to treatment, as well as to aid in prognosis.

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