Background: Facioscapulohumeral muscular dystrophy (FSHD) is a progressive muscular dystrophy characterized by clinical heterogeneity in age at onset, rate of disease progression, and severity of phenotypic manifestations. Currently, there are no patient-reported outcome measures available that correlate disease severity with risk of progression to functional outcomes such as wheelchair use. Development of a tool to predict disease progression could also have implications for clinical trial stratification.
Objective: We developed a patient-reported functional ability scale based on expert input to assess functional abilities in four domains commonly affected in FSHD: facial weakness, arm function, leg function, and mobility/transfers, which can be used to track disease progression.
Results: We analyzed prospectively-collected de-identified data from 578 individuals with genetically confirmed FSHD type 1 (FSHD1) enrolled in the US National Registry for FSHD (The Registry) that included an average of 9 years (range 0-18) of follow-up surveys. Participants completed the functional ability scale at enrollment and annually thereafter, in addition to other metrics that were collected as part of The Registry including age, sex, genetics (D4Z4 repeat size) and ambulatory status (wheelchair use). Initial functional scores (IFS) at enrollment were calculated and stratified into mild impairment (4-8), moderate (9-13) or severe (14-19), with a maximum score of 19. Excluding individuals who used a wheelchair at enrollment in The Registry (leaving 354/578 individuals), we found that individuals with higher IFS scores at enrollment were significantly more likely to progress to wheelchair use (p < 0.0001; HR 24.67). When separated by sex, females were more likely to progress to wheelchair use (p = 0.03, HR 6.48) independent of IFS (p < 0.001; HR 38.35). Stratification by small allele size and sex did not predict progression to wheelchair use. Conclusions: This patient-reported functional ability scale can be quickly and easily completed by individuals with FSHD to monitor disease progression and predict progression to wheelchair use. Use of an individual’s IFS may have implications for stratification in clinical trials.