F03 Characterising Upper Limb Movements In Huntington's Disease And The Impact Of Restricted Visual Cues

Abstract

Background Voluntary motor deficits are a common feature in Huntington’s disease (HD), characterised by movement slowing and performance inaccuracies. This deficit may be exacerbated when visual cues are restricted. Aims To characterise the upper limb motor profile in HD with various levels of difficulty, with and without visual targets. Methods/techniques Nine pre-symptomatic HD (pre-HD), nine early symptomatic HD (symp-HD) and nine matched controls completed a motor task incorporating Fitts’ law, a model of human movement enabling the quantification of movement timing, via the manipulation of task difficulty (i.e., target size, and location). The task required participants to make reciprocal movements between two circular targets, presented on a touch screen computer. After 10 movements, visual cues were removed, and participants continued movements based on their recollection of target location. Results/outcome Symp-HD showed significantly prolonged movement times compared with controls and pre-HD. Furthermore, movement planning was significantly impaired in symp-HD, compared with controls and pre-HD, evidenced by prolonged dwell times (time stationary between movements). Speed and accuracy were comparable across groups, suggesting that group differences observed in movement time and dwell time were evident over and above simple performance measures. No group differences were observed between cue conditions (with or without visual targets), suggesting that the restriction of visual cues may not result in a global deficit of motor planning. Conclusions Collectively these findings provide evidence of a deficiency in motor planning in symp-HD, suggesting that dwell time in particular may provide a more sensitive measure of motor dysfunction than speed and/or accuracy alone.