Landscape and Heterogeneity of Treatment Outcome Measures in Facioscapulohumeral Muscular Dystrophy: A Systematic Literature Review

Facioscapulohumeral muscular dystrophy is a rare genetic disorder that manifests as progressive weakening and loss of skeletal muscles, with the face, shoulder girdle, and upper arms typically affected in early stages. Currently, there are no approved therapies, and no consensus on the outcome measures used to assess disease progression or effects of new interventions. This systematic literature review identified treatment outcomes used to date, and the extent of their psychometric validation. Electronic searches were executed from inception to October 2022, supplemented with manual searches of relevant conferences. Eligible studies evaluated patients with the disease; reported on treatment outcomes or their validation; were clinical trials or observational studies; and published in English. Across the 65 studies identified reporting on treatment outcomes, 89 measures were used to assess outcomes following interventions in patients with the disease, including 58 efficacy/effectiveness, 6 safety, and 25 humanistic outcomes. Only 22/89 treatment outcomes were previously validated. Measures of motor function, upper/lower limb function, and muscle strength were the most frequently used efficacy and effectiveness measures. Significant heterogeneity exists among outcomes used. A total of 38 full text articles and 15 conference abstracts reported data on the humanistic burden in FSHD. The most reported domains included general QoL, followed by fatigue then pain. QoL was assessed in both adult and pediatric FSHD patients, with some instruments developed exclusively for use among children and adolescents (for example, Kidscreen for general QoL and the FSHD-HI Peds for disease-specific QoL). Based on the available evidence, it is evident that FSHD impacts QoL, with pain and/or fatigue impacting QoL. 18 studies were identified that reported on economic burden. While limited, the available evidence suggests that FSHD is associated with a substantial economic burden for patients, their caregivers and society. Overall, the findings of this SLR indicate that despite being the second most prevalent form of muscular dystrophy, FSHD is not well characterized in the literature. Further effort is needed to build consensus around the most relevant measures, such that trials for emerging interventions are designed with the consistent evaluation of patient-relevant benefits in mind.