Effectiveness of motor unit potentials classification using various parameters and indexes

Objectives: The aim of this study was to compare the effectiveness of quantities such as amplitude, duration, area, size index, number of peaks and irregularity coefficient applied to the classification of motor unit action potentials (MUAPs) in neuromuscular disorders. Methods: We have analyzed 215 potentials recorded from 20 neurogenic patients and 240 potentials recorded from 14 myogenic patients. The statistical values for each parameter and correlation coefficients between parameters have been analyzed. Results: The percentages of potentials unclassified by amplitude, duration, area/amplitude, area and size index were 31, 34, 28, 15 and 15%, respectively. Neither the number of phases and turns nor the irregularity coefficient may be used for the differentiation between neuro- and myogenic groups. There was also a set of MUAPs that were not properly classified by any of the above parameters. Among the unclassified potentials there were more potentials from myogenic cases. These unclassified myogenic MUAPs were predominantly irregular, whereas most of the unclassified neurogenic MUAPs were simple. In neurogenic cases, parameters describing the size of the potential (amplitude, duration, area) were not significantly correlated with those describing the shape (number of phases and turns), whereas in myogenic cases some correlation between these parameters was significant. Conclusions: MUAP quantities, due to the different correlation between them in myogenic and neurogenic disorders, have different sensitivities. Indexes were more sensitive than simple parameters and were also much more effective in the evaluation of atypical potentials