Issues & opinions: Are fibrillation potentials and positive sharp waves the same? No

Electrodiagnostic medicine consultants report electrical activity in muscle recorded at rest and during voluntary movement by means of waveform and firing rate characteristics. This principle allows us to distinguish fibrillation potentials from positive sharp waves. Although in most cases these two potentials have the same clinical significance, there are at least five different situations in which they do not have an identical meaning: (1) positive sharp waves can be recorded earlier after a peripheral nerve injury than can fibrillation potentials; (2) occasionally, nonclinically significant diffuse positive sharp wave activity may be seen in the absence of fibrillation activity (i.e., "EMG disease"); (3) positive sharp waves may be seen in distal muscles of "normal" subjects without the presence of fibrillation activity or clinical significance; (4) positive sharp waves without fibrillation potentials may be seen following local muscle trauma; and (5) positive sharp waves may be seen alone in some demyelinating polyneuropathies. By accurately describing the observed potentials, the electrodiagnostic medicine consultant may be able to obtain more clinically useful information from an electrodiagnostic study.