Cranial Nerve Thinning Distinguishes RFC1‐Related Disorder from Other Late‐Onset Ataxias.

Background: RFC1‐related disorder (RFC1/CANVAS) shares clinical features with other late‐onset ataxias, such as spinocerebellar ataxias (SCA) and multiple system atrophy cerebellar type (MSA‐C). Thinning of cranial nerves V (CNV) and VIII (CNVIII) has been reported in magnetic resonance imaging (MRI) scans of RFC1/CANVAS, but its specificity remains unclear. Objectives: To assess the usefulness of CNV and CNVIII thinning to differentiate RFC1/CANVAS from SCA and MSA‐C. Methods: Seventeen individuals with RFC1/CANVAS, 57 with SCA (types 2, 3 and 6), 11 with MSA‐C and 15 healthy controls were enrolled. The Balanced Fast Field Echo sequence was used for assessment of cranial nerves. Images were reviewed by a neuroradiologist, who classified these nerves as atrophic or normal, and subsequently the CNV was segmented manually by an experienced neurologist. Both assessments were blinded to patient and clinical data. Non‐parametric tests were used to assess between‐group comparisons. Results: Atrophy of CNV and CNVIII, both alone and in combination, was significantly more frequent in the RFC1/CANVAS group than in healthy controls and all other ataxia groups. Atrophy of CNV had the highest sensitivity (82%) and combined CNV and CNVIII atrophy had the best specificity (92%) for diagnosing RFC1/CANVAS. In the quantitative analyses, CNV was significantly thinner in the RFC1/CANVAS group relative to all other groups. The cutoff CNV diameter that best identified RFC1/CANVAS was ≤2.2 mm (AUC = 0.91; sensitivity 88.2%, specificity 95.6%). Conclusion: MRI evaluation of CNV and CNVIII using a dedicated sequence is an easy‐to‐use tool that helps to distinguish RFC1/CANVAS from SCA and MSA‐C. [ABSTRACT FROM AUTHOR]