Reliability and Validity of the Reachable Workspace Total Score With Wrist Weight in Facioscapulohumeral Muscular Dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by relentlessly progressive muscular weakness, impacting patients' daily functioning, health-related quality of life (HRQoL), and activities of daily living (ADLs), particularly those that require upper extremity (UE) function. Reachable workspace (RWS) is a performance outcome (PerfO) measure for UE function in FSHD. This study aimed to explore the reliability and validity of RWS average (for both arms) Total relative surface area (RSA) Q1-Q5 with 500 g wrist weight score ("Total Q1-Q5 RSA score") in FSHD. Data were sourced from the Phase 2 ReDUX4 clinical trial. Test-retest reliability and convergent validity of the Total Q1-Q5 RSA score were evaluated. The following outcome measures were included in the analyses: Timed up and go (TUG) and FSHD TUG, manual dynamometry, FSHD-health index, patient's global impression of change, Ricci Clinical Severity Scale (CSS), and musculoskeletal magnetic resonance imaging (MRI). Almost perfect test-retest reliability (ICC = 0.98) and good convergent validity with moderate (|r| ≥ 0.3) correlations with most ADL items, clinical severity and UE muscle strength were shown. Psychometric evidence supports the reliability and validity of the Total RSA Q1-Q5 score as a measure of UE function in FSHD and contributes to the evidence for its use as an outcome in clinical trials of FSHD. Additional study is required to explore responsiveness to change.