Limited responsiveness related to the minimal important difference of patient-reported outcomes in rare diseases

OBJECTIVES: To explore the responsiveness of patient-reported outcomes (PROs) in interventional studies involving patients with rare lysosomal storage diseases (LSDs). STUDY DESIGN AND SETTING: We searched eight databases for experimental and nonexperimental studies. Pairs of trained reviewers independently screened articles and subsequently extracted data from the eligible studies. Among studies with 10 or more patients using a valid PRO, we assessed the responsiveness of PROs based on a reanalysis of the data using minimal important difference estimates. Our analyses focused on statistically significant within-group differences in PROs for observational studies or the statistically significant between-group differences in PRO scores for controlled studies. RESULTS: Of 2,679 unique records, 62 interventional studies addressing patients with Fabry (55%), Gaucher (19%), Pompe (16%), and mucopolysaccharidoses (11%) proved eligible. The most frequently used PROs were the Short-Form-36 (25 studies), Brief Pain Inventory (20 studies), EuroQoL-5D (9 studies), and the Fatigue Severity Scale (6 studies). Observational studies suggest that PROs sometimes detect significant within-group changes when present. Randomized trials raise questions regarding the responsiveness of PROs to small differences between groups. CONCLUSIONS: Most studies have relied on generic PROs to evaluate quality of life and symptoms in patients with rare LSDs. PROs appear more responsive in observational studies than randomized trials.