THE DISTRIBUTION OF MUSCULAR WEAKNESS IN UPPER MOTOR NEURON LESIONS AFFECTING THE ARM

TLDR

The study measured the strength of 12 arm muscle groups to map the distribution of upper motor neuron weakness in humans. Three groups were studied: 14 intact volunteers, 10 patients with unilateral arm paresis, and 6 patients with severe arm paralysis, with bilateral measurements for volunteers and unilateral for the intact arm. Contralateral weakness varied among patients, with shoulder muscles relatively spared and wrist/finger flexors markedly weakened, while ipsilateral muscles were also reduced, refining clinical descriptions of upper motor neuron weakness and suggesting pathophysiological implications.

Abstract

SUMMARY The strength of 12 muscle groups of the arm was measured to determine the distribution of upper motor neuron weakness in man. Three groups of subjects were studied 14 intact volunteers (both sides recorded), 10 patients with unilateral arm paresis (both sides recorded) and 6 patients with severe paralysis of the arm (the 'intact' arm only measured). On the side contralateral to the causative lesion the pattern of weakness was not the same in all patients. Shoulder muscles were relatively spared while the wrist and finger flexors were relatively severely affected, the difference being statistically significant. In hemiparetic and hemiplegic patients the strength of muscles ipsilateral to the lesion was reduced compared with normal controls. These observations refine previous clinical descriptions of upper motor neuron weakness and have implications for its pathophysiology.