Stage‐Specific Health Status in Multiple System Atrophy: EQ ‐ 5D Findings from a European Cohort

Abstract Background Multiple system atrophy (MSA) is a rare neurodegenerative disorder that severely impairs health‐related quality of life (HRQoL). Disease progression is assessed using the Unified Multiple System Atrophy Rating Scale Part IV (UMSARS IV), which defines five stages. However, stage‐specific HRQoL estimates, particularly health‐utility values, are unavailable. These estimates are essential for health‐economic evaluation of treatments and for supporting HRQoL as a clinical trial endpoint. Bayesian methods offer a practical approach for analyzing HRQoL in rare diseases. Objective To estimate EQ‐5D‐based health‐utility values across UMSARS IV stages in MSA. Methods EQ‐5D data from the European MSA Study Group cohort were analyzed. EQ‐5D‐3L responses were mapped to EQ‐5D‐5L health‐utility values using the German value set, where a value of 1 represents perfect health and lower or negative values indicate worse health. Bayesian modeling estimated stage‐specific health‐utility values, reporting posterior means and 95% credible intervals (CrI). Sensitivity analyses included alternative model specifications and imputations of missing UMSARS IV stages. Results Stage‐specific EQ‐5D‐5L health‐utility values were 0.672 (95% CrI 0.628–0.719) for UMSARS IV Stage 1, 0.606 (95% CrI 0.523–0.679) for Stage 2, 0.517 (95% CrI 0.416–0.615) for Stage 3, 0.262 (95% CrI 0.158–0.364) for Stage 4, and 0.084 (95% CrI −0.045 to 0.217) for Stage 5. Bayesian models demonstrated good fit, capturing variability within stages and across countries. Sensitivity analyses confirmed robustness, with health‐utility values reflecting expected MSA progression. Conclusions This study is the first to provide stage‐specific health‐utility values across all UMSARS IV stages, enabling health‐economic evaluations of emerging interventions and supporting HRQoL as a clinical trial endpoint. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.