What is spontaneous activity in nerve conduction studies?

Updated: Aug 20, 2018
  • Author: Stephen Kishner, MD, MHA; Chief Editor: Jonathan P Miller, MD  more...
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Answer

Resting or spontaneous activity is the electrical activity present when the muscle is at rest and the electrode is not being moved. This includes both normal and abnormal spontaneous activity.

Normal muscle should be silent after the needle is inserted; however, if the needle happens to be near the neuromuscular junction, miniature endplate potentials or endplate potentials may be heard or seen. The most common abnormal spontaneous activity is reported as a gradation of either positive sharp waves (PSWs) or fibrillation potentials on a scale of 1+ (transient but reproducible discharges) to 4+ (abundant spontaneous potentials).

Fibrillations result from motor axonal loss that is not balanced by reinnervation. Conditions that cause this include any nerve disorder that affects the motor axon, inflammatory myopathies, and direct muscle injury. Depending on the amplitude of the PSWs and/or fibrillation potentials, the electromyographer can determine how recently the injury to the nerve occurred. Low-amplitude fibrillation potentials suggest that denervation occurred in the remote past, whereas high-amplitude fibrillation potentials suggest an ongoing active denervation process.


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