Lower Motor Neuron Changes Related to Upper Motor Neuron Lesion: Evidence from Electrophysiological Study in Patients with Hemiplegia

The purposes of our study were to evaluate whether patients with upper motor neuron lesion have functional changes in lower motor neurons, as reflected on nerve conduction velocity (NCV) study and electromyography (EMG), and to investigate the significance of the changes. Twenty-nine patients with hemiplegia due to cerebrovascular accident were included. The patients' ages ranged from 43 to 80 years (average, 61.8±10.9yr). Patients with history or physical findings of peripheral nerve involvement were excluded. Nerve conduction studies of median nerve and ulnar nerve in upper extremities, and tibial nerve and peroneal nerve in the lower extremities, were performed. EMG studies of abductor pollicis brevis and tibialis anterior of the patients with hemiplegia were also carried out. Our nerve conduction studies revealed a significant decreasing in compound motor action potential (CMAP) amplitude of the median and ulnar nerves (p＜0.01), and a significant decreasing in NCV of tibial motor nerve on the hemiplegic side (p＜0.05). EMG examination revealed spontaneous activities in 54% of the hand muscles and 43% of the leg muscles studied on the hemiplegic side. Spontaneous activities tended to occur simultaneously in the upper and lower limb muscles (p＜0.05). Our study supports the hypothesis that there are functional changes in the lower motor neurons as a result of an upper motor neuronal lesion.