Convergent validity, responsiveness, and meaningful within-subject change of the PROM-Ataxia in spinocerebellar ataxias

Abstract Background The clinimetric properties of the Patient-Reported Outcome Measure of Ataxia (PROM-Ataxia) have only been partially explored. This study aimed to investigate its convergent validity, responsiveness, and minimal clinically important difference (MCID), as well as its discriminative ability at the earliest disease stages in different types of spinocerebellar ataxia (SCA). Methods Baseline and 1 year PROM-Ataxia data were obtained from three single-center cohort studies involving ataxic and pre-ataxic SCA1, SCA3, and SCA7 mutation carriers and healthy controls. Spearman correlations were assessed between PROM-Ataxia scores and the Scale for the Assessment and Rating of Ataxia, Inventory of Non-Ataxia Signs, SCA Functional Index, Cerebellar Cognitive Affective Syndrome Scale, 5-level EuroQoL 5-Dimensional Visual Analogue Scale, Patient Health Questionnaire−9, Unified Huntington Disease Rating Scale Part IV, and the Activities of Daily Living subscale of the Friedreich Ataxia Rating Scale. Responsiveness was evaluated using standardized response means (SRM), and MCIDs through anchor-based and distribution-based approaches. Results Seventy-six mutation carriers (20 SCA1, 40 SCA3, 16 SCA7) were included at baseline, with 68 completing the 1-year follow-up visit. PROM-Ataxia scores correlated moderately to strongly with other measures (ρ=0.46–0.89, p <0.001) and differentiated pre-ataxic individuals from healthy controls ( p <0.001). Over one year, PROM-Ataxia demonstrated a gradual average increase (+ 3.9, p =0.048) with considerable between-subject variability of change (SD=22.0) and low responsiveness (SRM=0.17). The MCID of the PROM-Ataxia total score was estimated at 9.8–12.7. Conclusion PROM-Ataxia already distinguishes pre-ataxic SCA mutation carriers from healthy controls in physical, ADL, and mental health domains, and demonstrates strong convergent validity. Although responsiveness at the group level was somewhat limited because of large interindividual variability, 1 year follow-up scores adequately reflected the individual patient’s global impression of change.