Postural limits of stability in premanifest and manifest Huntington's disease.

Background: Huntington's disease (HD) is associated with neuronal death in basal ganglia circuits important for postural control. Despite evidence of postural instability associated with HD, postural control at the limits of stability has not been investigated in this disease.

Objective: To use computerized dynamic posturography to measure postural control at the limits of stability during the premanifest and manifest stages of HD.

Methods: Patients with manifest HD, premanifest gene carriers, and matched controls stood on mechanically locked force plates while viewing a computer screen. The participant's estimated center of gravity was represented on the screen as a cursor along with eight target icons arranged in a circular pattern at the theoretical edge of limits of stability. On each trial, one of the eight targets was highlighted and the participant was instructed to control the cursor by rapidly shifting his/her weight in the direction of the target. Measures included reaction time, movement velocity, endpoint excursion, maximum excursion, and directional control.

Results: Analysis of variance revealed significant impairment on endpoint excursion, maximum excursion, and directional control (p≤0.001) in the Huntington's disease group, but not in the premanifest gene carrier group as compared to controls. No differences were found on reaction time or movement velocity measures. Group signal to noise ratios also were examined for the measures.

Conclusions: HD patients, but not premanifest gene carriers, showed impaired postural control at the limits of stability. Impaired performance in HD patients has potential functional consequences including increased risk of falling during weight-shifting activities.