TABLE 1

Commonly observed or notable abnormal spontaneous activity

TermDescriptionClinical significance
Fibrillation potentials and positive sharp wavesSpontaneous muscle fiber potentials recorded during rest; morphology and firing regularity determine categorization as fibrillation potentials or positive sharp wavesMuscle fibers are remaining without innervation, generally a sign of recent or ongoing denervation in neurogenic conditions
In myopathic conditions, they may indicate inflammatory or necrotizing myopathies
Fasciculation potentialsSpontaneous, irregularly firing motor unit dischargesMay be seen occasionally in chronic neurogenic conditions of any kind, but are seen more diffusely in disorders of the anterior horn cell and motor neuron disease
Myotonic dischargesSingle muscle fiber firing repetitively in a waxing andwaning pattern at high frequencyWhen diffuse and prominent, indicates a myotonic disorder
Can also rarely be seen in any chronic neurogenic or myopathic condition
Complex repetitive dischargesTime-locked repetitive firing of a group of muscle fibers, with sudden start and stop of burstsVery chronic neurogenic or myopathic conditions
Neuromyotonic dischargesSingle motor unit firing repetitively at a very high frequencyTypically, disorders of voltage-gated potassium channels
Myokymic dischargesSingle motor unit firing in regularly recurring burstsMost commonly associated with chronic demyelination and radiation plexopathy