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 (α = 0.88; α = 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 × 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 Registration: ClinicalTrials.gov identifier, NCT03701399 (Study 206).