Measurement Properties of the Friedreich Ataxia Rating Scale in Patients with Spinocerebellar Ataxia

Introduction: The Friedreich Ataxia Rating Scale-Activities of Daily Living (FARS-ADL) is a valid, highly utilized measure for assessing ADL impacts in patients with Friedreich ataxia. We provide evidence of the psychometric validity of the FARS-ADL in two cohorts of patients with spinocerebellar ataxia (SCA). Methods: Using data from a cohort of real-world subjects with SCA (recruited at Massachusetts General Hospital [MGH]; n = 33) and a phase 3 trial of troriluzole in adults with SCA (NCT03701399 [Study 206]; n = 217), comprising a subset of patients with the SCA3 genotype (n = 89), the psychometric measurement properties and minimal change thresholds of the FARS-ADL were examined. Results: Ceiling effects for the FARS-ADL were absent within the MGH cohort while floor effects were observed for eight of nine items. Excellent internal consistency reliability was observed (alpha(total) = 0.88; alpha(items-removed) = 0.86-0.87), and item-to-total correlations were acceptable (r = 0.55-0.89 per item). Convergent and divergent validity were supported with strong correlations demonstrated between FARS-ADL and scales measuring similar concepts (Neuro-QOL [Upper], Neuro-QOL [Lower], PROM-ADL, PROM-PHYS, and FARS-FUNC; all P < 0.001) and weaker correlations shown between measures of differing constructs. A two- to three-point threshold for meaningful changes was supported as 0.5 x SD = 2.43, SEM = 2.19. Mean changes from baseline for subjects classified as "improved," "no change," or "deteriorated" were -0.54, 0.22, and 1.47, respectively. Similar trends were observed in the Study 206 all-SCA and SCA3 cohorts. Conclusion: Psychometric evaluation showed that the FARS-ADL performed well on analyses examining the reliability and validity of the measure and can detect meaningful changes in patients with SCA, including those with SCA3. Trial RegistrationClinicalTrials.gov identifier, NCT03701399 (Study 206).