The spinal and bulbar muscular atrophy-health index: a disease-specific outcome measure

Objective: Basic science research in spinal and bulbar muscular atrophy (SBMA) has facilitated the development of disease modifying therapeutics. However, there remains a need for disease-specific patient-reported outcome (PROs) measures to monitor changes in disease status. The spinal and bulbar muscular atrophy-health index (SBMA-HI) was designed to address this gap. Methods: Initial interviews with 21 individuals with SBMA and a subsequent international cross-sectional study with 232 participants were conducted to identify the most prevalent and impactful symptoms in SBMA. The most relevant symptoms were included in the SBMA-HI. We subsequently used patient interviews, test-retest reliability evaluation, known groups validity testing, and factor analysis to evaluate and optimize the SBMA-HI. Results: The SBMA-HI tool includes fourteen subscales and one supplemental subscale (for those who are able to ambulate independently) to measure SBMA disease burden from the patients' perspectives. Fifteen adults with SBMA participated in semi-structured beta interviews and found the SBMA-HI to be clear and relevant to them. Twenty-nine adults with SBMA participated in test-retest reliability assessments, which demonstrated high reliability of the SBMA-HI. The final SBMA-HI and its subscales demonstrated a high internal consistency. Conclusion: The SBMA-HI is a reliable disease-specific patient-reported outcome measure capable of quantifying disease burden in SBMA.