POLYPHASIC action potentials with high amplitude are common in the electromyograms of patients with neurogenic disorders, such as in Charcot-Marie-Tooth disease and hereditary proximal spinal muscular atrophy. On the other hand, a pattern of double discharge is often noted in tetany and some other conditions.1
Occasionally, a specific pattern is found in the same electromyogram (EMG) of some neurogenic muscular atrophies. This pattern consists of two coupled discharges of different shape with constant interval in a long recording. The first discharge is large and often polyphasic, and the second is extremely small and monophasic or biphasic. This pattern of EMG seems to be completely different from the pattern of double discharge that is generally considered to be two repetitive firings of one neuromuscular unit in quick succession.2 Moreover, this specific pattern is differentiated from the polyphasic action potential by the intermittent disappearance of the secondary small discharge. The