Psychomotor and non-motor correlates of cognition in spinocerebellar ataxias Types 1, 2, 3, and 6

There is growing evidence of cognitive deficits in spinocerebellar ataxias, with the Cerebellar Cognitive Affective Syndrome Scale (CCAS-S) an increasingly common measure of this dysfunction. There remain ongoing questions as to how Cerebellar Cognitive Affective Syndrome Scale performance relates to day-to-day cognitive function, non-motor and motor features of spinocerebellar ataxias and demographic factors. Via an online study, we evaluated Cerebellar Cognitive Affective Syndrome Scale performance amongst individuals with spinocerebellar ataxia Type 1 (n = 14), Type 2 (n = 16), Type 3 (n = 18), and Type 6 (n = 26) relative to demographically-matched control groups. Furthermore, amongst individuals with spinocerebellar ataxia, we examined associations between performance and (i) age and education, (ii) ataxia motor severity, (iii) psychomotor function measured by computerized finger tapping and reaction time tasks and (iv) self-rated cognition, depression, emotional regulation, psychosocial function and fatigue. Cerebellar Cognitive Affective Syndrome Scale performance was significantly reduced in spinocerebellar ataxia Types 2, 3, and 6 compared to controls, although substantial inter-individual variability in performance was observed in the spinocerebellar ataxia cohort (43.2%/24.3%/21.6%/10.8% met criteria for Definite, Probable, Possible, and No CCAS). Performance in individuals with spinocerebellar ataxias correlated significantly with self-reported ataxia motor severity, fine motor speed, psychomotor trial-by-trial variability, and one of two measures of day-to-day cognitive function. Significant correlations were not observed against age, education, age at disease onset, disease duration, psychomotor reaction time, depression, emotional regulation, psychosocial function, or fatigue. We present evidence that motor function and psychomotor variability are more important correlates of inter-individual variability in cognitive performance amongst people with spinocerebellar ataxia Types 1, 2, 3 and 6, compared to demographic factors, fatigue, or emotional function. Importantly, formalized cognitive testing using the Cerebellar Cognitive Affective Syndrome Scale correlates with self-reported cognitive functioning. This study highlights cognitive dysfunction as a functionally impactful feature of certain spinocerebellar ataxias, and motivates further investigation into the disease- and individual-specific profiles of cognitive impairment in this population.