Needle EMG · Core

Recognize activity at rest

Spontaneous activity

Describe regularity, morphology and firing pattern before assigning pathological meaning.

3 learning sectionsCompiled 2026-09-08English edition · Traditional Chinese available

01Single muscle fibers

  • Fibrillation potentials and positive sharp waves indicate muscle-fiber membrane instability. They occur with denervation and some myopathies.
  • Endplate noise and spikes are physiological and may accompany local discomfort. Do not confuse them with fibrillations.

02Motor units and grouped activity

  • Fasciculations are spontaneous motor-unit discharges; their presence alone does not establish ALS.
  • Myokymia has grouped firing. Neuromyotonia may show high-frequency trains with decrementing frequency or amplitude.

03Special patterns

  • Myotonic discharges often wax and wane in frequency and amplitude and are not specific to one disease.
  • Complex repetitive discharges have relatively regular repeating morphology and often abrupt onset and offset; etiological specificity is limited.

Pause and explain

Explain in your own words: “Name the discharge, then describe its distribution and clinical significance.” Then think of a situation in which it could be misinterpreted.

Show a review prompt

The amount of spontaneous activity cannot be converted into an exact date of onset.

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References and further reading

Educational synthesis; independent neuromuscular specialist review is pending. Publication dates and compilation dates are distinct. This is an original teaching synthesis; consult the source for complete methods and criteria.