The Facioscapulohumeral Muscular Dystrophy-Health Index: Development and evaluation of a disease-specific outcome measure

Abstract

Introduction/Aims: As promising therapeutic interventions are tested among patients with facioscapulohumeral muscular dystrophy (FSHD), there is a clear need for valid and reliable outcome tools to track disease progression and therapeutic gain in clinical trials and for clinical monitoring. Our aim was to develop and validate the Facioscapulohumeral Muscular Dystrophy-Health Index (FSHD-HI) as a multifaceted patient-reported outcome measure (PRO) designed to measure disease burden in adults with FSHD. Methods: Through initial interviews with 20 individuals and a national cross-sectional study with 328 individuals with FSHD, we identified the most prevalent and impactful symptoms in FSHD. The most relevant symptoms were included in the FSHD-HI. We used patient interviews, test–retest reliability evaluation, known groups validity testing, and factor analysis to evaluate and optimize the FSHD-HI. Results: The FSHD-HI contains 14 subscales that measure FSHD disease burden from the patient's perspective. Fourteen adults with FSHD participated in semistructured beta interviews and found the FSHD-HI to be clear, usable, and relevant to them. Thirty-two adults with FSHD participated in test–retest reliability assessments, which demonstrated the high reliability of the FSHD-HI total score (intraclass correlation coefficient = 0.924). The final FSHD-HI and its subscales also demonstrated a high internal consistency (Cronbach α = 0.988). Discussion: The FSHD-HI provides researchers and clinicians with a reliable and valid mechanism to measure multifaceted disease burden in patients with FSHD. The FSHD-HI may facilitate quantification of therapeutic effectiveness, as demonstrated by its use as a secondary and exploratory measure in several clinical trials.