Normal and abnormal spontaneous activity

Assessment of spontaneous waveforms recorded in a resting muscle during needle electromyography is important to determine the type of underlying neuromuscular disorder, temporal course of a disease, and severity and prognosis. A variety of different spontaneous waveforms may be recorded. Some waveforms may be recording in patients without neuromuscular disorders, such as end-plate activity or fasciculation potentials, while others occur only in abnormal muscles. Fibrillation potentials are the most common abnormal spontaneous waveform and are encountered in a wide variety of neuromuscular disorders causing denervation or damage to muscle fibers. Myotonic discharges, when diffuse, are seen in a small number of myopathies or muscle channelopathies. Complex repetitive discharges are nonspecific spontaneous waveforms that may be encountered in chronic or longstanding neurogenic or myopathic disorders. Myokymic and neuromyotonic discharges are rare spontaneous waveforms that suggest either focal or diffuse peripheral nerve hyperexcitability. When interpreted in conjunction with voluntary motor unit potentials as well as nerve conduction study findings, spontaneous waveforms are useful to fully assess the types of disorders of patients with neuromuscular complaints.