OBJECTIVE: To estimate the association between function, measured by NSAA score, and health state utility, measured by HUI2 and HUI3 score, among patients with DMD.
BACKGROUND: DMD is a rare neurodegenerative disease with relentless, progressive functional loss dramatically affecting health-related quality-of-life (HRQoL). Data on utility scores (dead=0 and full health=1), reflecting preferences for HRQoL implications of health states, are limited and the relationship between function and utility is unclear.
METHODS: Family members serving as proxy respondents for ambulatory boys with DMD (recruited under NCT01254019, BioMarin Pharmaceuticals Inc) completed the HUI; and the NSAA (scored from 0-34), by trained assessors. Only placebo-treated boys were included in this analysis. Mean baseline and change over time scores were computed and the correlation between HUI2 and HUI3 utility, and NSAA, at baseline and 48 weeks was calculated using Spearman’s coefficient. The analyses were also conducted for each HUI attribute individually with NSAA score.
RESULTS: Baseline mean (range) ages was 8.0 (5-16; n=61) years and mean (SD) scores were 0.87 (0.13; HUI2), 0.82 (0.19; HUI3), and 21.0 (8.1; NSAA). Mean change over 48 weeks was -0.05 (0.14; HUI2), -0.06 (0.19; HUI3), and -2.9 (4.7; NSAA). Weak positive correlations were observed between baseline NSAA score and overall HUI utility (HUI2: r=0.29, HUI3: r=0.17), and on change over 48 weeks (HUI2: r=0.16, HUI3: r=0.15). Moderate positive correlations were observed between NSAA score and the HUI3 ambulation (r=0.41), HUI2 mobility (n=0.41), and HUI2 self-care (r=0.42) scores; NSAA scores were weakly correlated with HUI3 pain (r=-0.20).
CONCLUSIONS: Among these ambulatory DMD boys, NSAA is not strongly correlated with overall HUI utility, however there were stronger correlations with individual domains including ambulation, mobility and ability for self-care. This suggests that additional important drivers of utility exist; and functional status alone cannot solely explain HUI utility estimates in ambulatory DMD patients.