Background Assessment of motor phenotype and diagnosis of Huntington's Disease (HD) are based on the Unified HD Rating Scale-Total Motor Score, a categorical scale. We have previously shown that impairments in tongue protrusion forces can be seen in premanifest and manifest HD and correlate with clinical severity as assessed by the Unified HD Rating Scale-Total Motor Score and the disease burden score (Reilmann et al. 2010). In this study we aimed to investigate whether similar impairments of force coordination can be found in different force matching tasks.

Objective To assess whether impairments in isometric force coordination of the upper and lower extremities can be detected in manifest HD gene carriers compared to controls.

Methods Using a precalibrated force transducer, the ability of subjects with symptomatic HD (n=31) to generate and maintain isometric TPF at different target force levels (1.5, and 5.0 N for thumb, 1.0, 5.0 and 10.0 N for big toe) was assessed and compared with age-matched controls (n=22) in a cross-sectional pilot study.

Results All paradigms distinguish controls from symptomatic subjects. The static coefficient of variability (%), assessing the degree of deviation from the target force normalised to the mean force, was the most robust measure in all matching trials. Comparisons between tasks and correlations with clinical measures such as the TMS, DBS and TFC will be presented.

Conclusions Assessment of force matching tasks by hand and feet may provide quantitative objective measures for severity of motor phenotype in symptomatic HD.