Reliability and minimal detectable change of physical performance measures in individuals with pre-manifest and manifest Huntington disease

Background: Clinical intervention trials in people with Huntington disease (HD) have been limited by a lack of reliable and appropriate outcome measures. Objective: The purpose of this study was to determine the reliability and minimal detectable change (MDC) of various outcome measures that are potentially suitable for evaluating physical functioning in individuals with HD. Design: This was a multicenter, prospective, observational study. Methods: Participants with pre-manifest and manifest HD (early, middle, and late stages) were recruited from 8 international sites to complete a battery of physical performance and functional measures at 2 assessments, separated by 1 week. Test-retest reliability (using intraclass correlation coefficients) and MDC values were calculated for all measures. Results: Seventy-five individuals with HD (mean age=52.12 years, SD=11.82) participated in the study. Test-retest reliability was very high (>.90) for participants with manifest HD for the Six-Minute Walk Test (6MWT), 10-Meter Walk Test, Timed “Up & Go” Test (TUG), Berg Balance Scale (BBS), Physical Performance Test (PPT), Barthel Index, Rivermead Mobility Index, and Tinetti Mobility Test (TMT). Many MDC values suggested a relatively high degree of inherent variability, particularly in the middle stage of HD. Minimum detectable change values for participants with manifest HD that were relatively low across disease stages were found for the BBS (5), PPT (5), and TUG (2.98). For individuals with pre-manifest HD (n=11), the 6MWT and Four Square Step Test had high reliability and low MDC values. Limitations: The sample size for the pre-manifest HD group was small. Conclusions: The BBS, PPT, and TUG appear most appropriate for clinical trials aimed at improving physical functioning in people with manifest HD. Further research in people with pre-manifest HD is necessary