Purpose: This study aimed to elucidate the relationship between motor function and quality of life (QoL) in patients with Duchenne muscular dystrophy (DMD), using the North Star Ambulatory Assessment (NSAA) and the EuroQol 5-Dimension 3-Level (EQ-5D-3L) utility score.
Background: DMD is a genetic disorder associated with progressive muscle degeneration due to lack of dystrophin. The NSAA is a standardized assessment tool for evaluating motor function and tracking disease progression in individuals with DMD. Higher scores on the NSAA indicate better motor function. The EQ-5D-3L measures health status across five dimensions and is used to evaluate overall health-related quality of life (QoL). By mapping NSAA total scores onto EQ-5D-3L utility score, we sought to gain valuable insights into the impact of motor function on individuals’ health status and quality of life.
Methods: A repeated measures longitudinal model was employed to estimate the relationships between the EQ-5D-3L utility score and the NSAA total score. Preference weights for the United States were used to calculate the EQ-5D-3L utility score. Data from a completed DMD interventional study were collected from initial screening and from follow-ups at week 13, 25 49, and 73. In total, 136 observations from 53 subjects were modeled in the analysis.
Results: The model with NSAA total score as a continuous predictor demonstrated a robust relationship between NSAA total score and EQ-5D-3L utility score (p<0.001). The following equation describes relationship between continuous NSAA and EQ-5D-3L utility scores: EQ-5D-3L = 0.5523 + 0.01312 × NSAA (both intercept and slope are significant with P<0.0001).
Conclusion: An approximately linear relationship was found between NSAA score and EQ-5D-3L utility scores. The study indicates that NSAA is a validated measure for assessing motor function and a predictor of patients’ QoL.