Poster 19: Validation of the Modified Motor Score (mMS): A Subscale of the Unified Huntington's Disease Rating Scale (UHDRS) Motor Score

Background The UHDRS assesses various aspects of clinical function and capacity in Huntington's disease (HD). Items in the UHDRS motor section are heterogeneous, relate to various aspects of HD motor symptoms, and can be categorized as eye, involuntary, or voluntary movements. Items relating to voluntary movements appear to correlate strongly with the extent of disability, whereas the correlation between chorea and disability is less pronounced. These findings are supported by a preliminary analysis of baseline data from a phase 2 study of pridopidine (ACR16) in patients with HD (ACR16C007). Methods Motor scales from the UHDRS motor section were analyzed according to their metric properties and correlation with measures of functional disability, assessed by total functional capacity (TFC) and functional assessment (FA) scales. The following motor scales were analyzed, using data from the CARE-HD study dataset: UHDRS motor section items (TMS); TMS excluding eye movements; modified motor scale (mMS: TMS excluding eye movements, chorea, and dystonia), which assessed voluntary movements; chorea; and eye movements. Results The mMS subscale correlated strongly with TMS (ρ = 0.89; p Conclusions The mMS subscale appears to be a valid modification of the UHDRS motor score and has functional relevance, as demonstrated by strong correlations with functional assessments. This subscale of the UHDRS motor sections may offer a simple method of assessing response to treatment in patients with HD.