Shape irregularity of motor unit potentials in some neuromuscular disorders.

The aim of this study was to test whether analysis of the irregularity of the motor unit potential waveform may supplement conventional evaluation. We have found that the irregularity is not a characteristic feature of potentials either in neurogenic disorders or in myopathy. We have found, however, that within myo- and neuropathic disorders, the irregularities differ between slow (such as Becker muscle dystrophy and chronic spinal muscle atrophy) and fast progressing processes (such as amyotrophic lateral sclerosis and Duchenne muscle dystrophy). These differences depend on the different number of phases and turns contributing to wave formation. In slowly progressing processes, very irregular potentials are more often polyphasic, whereas in acute processes they may be polyturn or polyphasic. The results suggest that it is the irregularity of the potential that provides new information, not available so far, on the activity of the pathological process.