Muscle tone in Huntington's disease

Tone was evaluated quantitatively in 39 patients with Huntington's disease (HD) by measuring resistance to passive elbow flexion and extension movements on a hydraulic testing device. A velocity dependent increase in resistance to passive elbow flexion and to a lesser extent in resistance to passive extension was found in 10 patients. Increase in muscle tone was related to disease duration but not to the age of the patients nor to the severity of choreatic movements or the amount of cognitive impairment. A hypertonic pattern could be observed also in patients without any medication, and seemed not to be related to neuroleptic treatment. The pattern of tone change in HD is compared to the pattern of hemispasticity in upper motor neuron syndrome and to that of Parkinson's disease. It appears that an increase in muscle tone, with a velocity dependent resistance to flexion more than extension movements, is a frequent feature in advanced stages of Huntington's disease.