Denervation activity in the EMG of patients with upper motor neuron lesions: time course, local distribution and pathogenetic aspects.

EMG denervation activity was studied in patients without peripheral neuron disorder but with upper motor neuron lesions. The time course of such central denervation activity, the local distribution and the quantitative relationship between denervation activity and the degree of paresis and spasticity were also studied. A total of 101 patients, who had developed hemiplegia or hemiparesis as a result of a cerebral vascular accident, underwent needle electromyographic examination at regular intervals in proximal and distal muscle groups. The maximum observation time was 1 year. Denervation activity in cases of central paresis first occurred 2-3 weeks after stroke. This could be observed most frequently in the distal arm and hand muscles. In the course of weeks and months the frequency of the denervation activity decreased in parallel with the development of spasticity and the increasing voluntary innervation. The occurrence and the dynamic properties of the denervation activity in cases of central paresis support the assumption of a trans-synaptic degeneration of alpha-motoneurons and of a compensating segmental "sprouting" of afferents.