Estimation of the relationship between the noninvasively detected activity of single motor units and their characteristic pathological changes by modelling.

Neuromuscular disorders are often related to specific changes in the structure of single motor units (MUs). One approach for the detection of these changes is high-spatial-resolution EMG (HSR-EMG), which allows non-invasive recording of the activity of a single MU. Early investigations with patients suffering from various neuromuscular disorders have shown that there is a distinct difference between the HSR-EMG signals of healthy volunteers, patients with muscular disorders, and patients with neuronal disorders. In this study, the relationship between typical HSR-EMG patterns and characteristic pathological changes in the structure of the MUs is considered. Therefore, a muscle model has been developed which is adapted to the physiological properties of the m. abductor pollicis brevis. The effects of the loss of single muscle fibres (muscular disorders) and the loss of entire MUs (neuronal disorders) on the HSR-EMG pattern have been simulated. These simulations show the same HSR-EMG patterns as seen in patients and healthy volunteers. As a consequence, it can be assumed that the muscle model is an appropriate tool for the simulation of HSR-EMG signals. Furthermore, the simulation results support the hypothesis that the typical changes in the HSR-EMG pattern found in patients with neuromuscular disorders can be attributed to the characteristic changes in the structure of the MUs.