Reaction time and rhythm of movement in Huntington's disease.

Huntington disease (HD) is characterized by several hyperkinesias though motor slowness is also another cardinal in this disease. In addition, self-paced timing movements are also disturbed in HD, which may also affect several rhythmic voluntary movements such as gait. Motor slowness can be measured with clinical scales such as the Unified Huntington's Disease Rating Scale (UHDRS) and timed tests, but also with the reaction time (RT) paradigm. We evaluated RT as a measure of motor slowness in 30 patients with genetically confirmed Huntington's disease and 24 control subjects. We also evaluated self-paced timing precision (SPTP) by applying a simple software program devised by our group. Clinical assessment was performed according to the UHDRS, including motor section, total functional capacity (TFC) and cognitive section (verbal fluency test, symbol digit, and Stroop test) The mean values obtained for RT and SPTP were statistically different in HD as compared with those from controls (p<0.0005). We observed a statistically significant correlation between RT and TFC scores (rs=-0.57, p<0.005 Spearman's correlation) and also between SPTP values and TFC scores (rs=-0.40, p<0.05 Spearman's correlation). In addition, RT and SPTP significantly correlated with cognitive scores (including digit symbol, verbal fluency and Stroop tests). Simple tests such as RT and SPTP provide an objective evaluation of motor impairment in HD yielding measures that correlate with clinical assessment and functional disability.