Validation of the SODA in Spinocerebellar Ataxia Type 2.

Oculomotor disturbances hallmark hereditary ataxias. While video-oculography provides biomarkers, clinical tools like the Scale for Ocular Motor Disorders in Ataxia (SODA) offer reliable, specific bedside assessment, but the scale has not been validated in specific subtypes of cerebellar ataxias. This study aimed to determine the usefulness of the SODA in a Cuban cohort of Spinocerebellar Ataxia type 2 (SCA2) patients and to assess relationship of SODA scores with disease severity scores and quality of life measures. The original SODA underwent forward and backward translation into Spanish, followed by a pilot study to assess comprehensibility. The validation study included evaluations of internal consistency, discriminant validity, and convergent validity in 47 individuals with SCA2 (9 in the prodromal stage) and 30 sex- and age-matched healthy controls. Complementary instruments assessed cerebellar and non-cerebellar motor parameters, cognitive function, and quality of life. Despite the SODA scale’s low internal consistency (α = 0.557) due to poor contribution from the saccadic intrusions, ocular alignment, and nystagmus items, it demonstrated excellent discriminant validity (p < 0.0001 vs. controls, including preclinical cases). The most frequent deficits were horizontal saccade slowing and dysmetria, observed in 95.7% of the whole cohort and 77.8% of preclinical carriers. The SODA score correlated significantly with the INAS oculomotor count (supporting concurrent validity), as well as SARA, CAG repeats, and quality-of-life measures. This study validates the SODA for detecting oculomotor deficits in SCA2, including prodromal stages. These findings underscore its potential as a bedside tool for tracking integrated disease burden in future clinical trials and management strategies.