Scanning EMG in normal muscle and in neuromuscular disorders

The spatial distribution of motor units in normal subjects and in patients with neurogenic and myogenic conditions was studied. The possibilities and the difficulties in quantifying the records are discussed. Normal values are presented for the brachial biceps and anterior tibial muscles. The results are compared to the previous multielectrode studies. The findings in pathological conditions compared to normals are evaluated. The scanning EMG verified the rearrangement of muscle fibres in abnormal muscles. The most striking finding was the presence of long polyphasic sections in abnormal muscles. However, this parameter did not differentiate neurogenic from myogenic cases. The length of the motor unit cross-section did not differ significantly in the abnormal muscles compared to normal. Thus, the size of motor unit territory does not seem to be a useful parameter to detect pathology. Scanning EMG gives a new dimension to exploring the motor unit characteristics not attainable by conventional methods and provides important information towards a better understanding of concentric needle EMG. Examples are shown from healthy subjects and from patients with neuromuscular diseases, both for the different parameters and special phenomena.