Validity and Reliability of Outcome Measures Assessing Dexterity, Coordination, and Upper Limb Strength in Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay

Objective To document in adults affected by autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) the intra- and interrater reliability, standard error of measurement, agreement, minimal detectable change, and construct validity of the 9-Hole Peg Test (NHPT), the Standardized Finger-to-Nose Test (SFNT), and grip strength. Design Metrologic study. Setting Neuromuscular rehabilitation clinic. Participants Genetically confirmed adult patients with ARSACS (N=42; 21 women; mean age, 38.6y). Interventions Not applicable. Main outcome measures Intra- and interrater reliability was determined using the intraclass correlation coefficient (ICC). Construct validity was determined by assessing the capacity of the NHPT, the SFNT, and grip strength to distinguish between participants based on sex, mobility stages, and age groups, and on performance on the Archimedes spiral and fast alternating hand movements tests. Results All 3 tests have shown excellent reliability (ICC=.90-.98). However, the limit of agreement was influenced by the participant's performance on the NHPT, and the minimal detectable change was very different for both hands (right=9.7 vs left=28.0). Construct validity was confirmed for the SFNT and NHPT, but it was not demonstrated for grip strength. Conclusions Given the metrologic properties assessed in this study, the SFNT is an excellent measure to assess upper limb coordination, whereas the NHPT must be used with caution. The grip strength is reliable but does not seem to reflect disease severity.