Double discharges of motor units in neuromuscular disorders

Repetitive discharges (RDs) are observed in electromyograms recorded from healthy as well as diseased muscles. We have evaluated the prevalence of RDs in some neuromuscular diseases and analysed the time parameters of recordings displaying RDs as well as shapes of the potentials. In our clinical material, RDs have been observed exclusively in lower motor neuron lesions, never in healthy or in myopathic muscles. The prevalence index of RDs in amyotrophic lateral sclerosis (0.06) was found to be different from that in chronic spinal muscle atrophy (0.004). The types of double potential shape have been categorised. The relationships between the amplitude of the second component and the interspike duration and that between the interspike duration and the jitter were calculated. The amplitude of the second component diminished and jitter of the components increased with the shortening of the interval between components. The authors suggest that in lower motor neuron lesions, the RDs of the motorunit (MU) may be one of the first signs of the MU's dysfunction.