Uncontrolled flailing of an arm is a symptom of?

Hemiballismus is associated with a lesion of the sub thalamic nucleus of the motor system. Lesions in this nucleus produce uncontrolled flailing and involuntary movement, especially of the upper extremity. Amyotrophic lateral sclerosis, a disease of the lower motor neurons, produces weakness in skeletal muscles, which may eventually lead to paralysis and muscle atrophy. Athetosis refers to slow writhing movements of the limbs. This finding is characteristic of lesions in areas of the basal ganglia that are not subthalamic.