The unified Huntington's Disease Rating Scale for advanced patients: validation and follow-up study

The Unified Huntington's Disease Rating Scale (UHDRS) adequately measures decline in patients at early and moderate stages of Huntington's disease (HD). In patients with advanced HD, floor effects hamper the evaluation, thus calling for an adjusted scale. We designed the UHDRS-For Advanced Patients (UHDRS-FAP) to improve longitudinal assessment of patients at the advanced disease stage. Sixty-nine patients with a Total Functional Capacity score ≤ 5 were recruited in France and the Netherlands. Among them, 45 patients were followed longitudinally (mean ± standard deviation, 1.6 ± 1.2 years) with the UHDRS-FAP; 30 patients also were assessed with the UHDRS. In cross-sectional analyses, the psychometric properties and inter-rater reliability of the scale were evaluated. Longitudinal analyses were used to evaluate the sensitivity to decline of the UHDRS-FAP compared with the UHDRS. Internal consistency was higher for motor (0.84) and cognitive (0.91) scores than for somatic (0.70) and behavioral (0.49) scores. Inter-rater reliability was ≥ 0.88 for all scores. The somatic score, which was specific to the UHDRS-FAP, declined over time along with motor and cognitive performance on both scales. Although performance with the two scales was correlated, the UHDRS-FAP appeared to be more sensitive to change and was the only scale that detected decline in patients with a Total Functional Capacity score ≤ 1. Neither scale detected a significant decline in behavioral scores. The results indicate that the UHDRS-FAP is reliable and more sensitive to change than the original UHDRS for cognitive and motor domains. It offers items that are relevant for daily care. Behavioral scores tended to decline, but this may reflect the decline in patients' communicative abilities.