The spectrum of motor disorders in Huntington's disease.

EMG of involuntary muscle contractions and their correlation with clinical pictures in Huntington's disease disclosed a series of motor disorder from chorea to parkinsonism. Irregular brief contractions appearing reciprocally in flexor or extensor muscles were observed in typical chorea with hypotonia. Tonic nonreciprocal contractions appeared in the rigid form. In athetoid movement or dystonic postures, more slowly nonreciprocal fluctuating contractions appeared. In some cases phasic contractions changed from a reciprocal to nonreciprocal pattern by psychic stress. In contrast to the activation of motoneurons in choreatic movements, involuntary brief suppression of voluntary contraction appears in typical chorea. Difference in involuntary movements and muscle tone may result from quantitative differences in involvement of striatal neurons which are the origin of parallel pathways proposed by DeLong and colleagues.