THE REORGANIZATION OF MOTOR UNITS IN MOTOR-NEURON DISEASE

We studied 78 patients with motor neuron disease (MND) using concentri c needle electromyography. Analysis on weak and maximal effort was per formed using our own, fully automated, computer method, EMG-LAB. In ad dition to the conventional parameters of single motor unit action pote ntials (MUAPs) and interference pattern, new criteria were applied: th e range of the acting motor units and the functional recruitment order . A total of 375 muscles of MND patients and 120 control muscles were investigated. The electromyographic data were analyzed separately in f ive groups of muscles, classified A, B, C, D, and E according to their clinical condition. Those results allowed us to discern six neurophys iological stages (N-0,N-1,N-2,N-3,N-4,N-5) from the early to the most advanced phase. It has been confirmed that reinnervation in MND is ade quate to compensate for the loss of over 50% of motor neurons but it i s only a transitory phase in the morbid course. At stages N0-5, the el ectrophysiological data reflect structural and functional integrity of the functioning motor units. Evaluation of not only single MUAPs but also of the full range of acting motor units and their recruitment ord er allowed a deeper look into the underlying pathophysiological mechan isms. (C) 1997 John Wiley & Sons, Inc.