Ocular Motor and Vestibular Profile in Spinocerebellar Ataxia Type 27B: Toward a Practical Bedside Diagnostic Framework

Spinocerebellar ataxia type 27B (SCA27B), caused by GAA repeat expansions in FGF14 , is an increasingly recognized form of late-onset cerebellar ataxia. However, early diagnosis remains challenging due to mild or absent cerebellar motor signs and often normal brain magnetic resonance imaging (MRI). Oculovestibular abnormalities, although prevalent, are frequently overlooked and not captured by standard clinical scales such as the Scale for the Assessment and Rating of Ataxia (SARA). This study aimed to perform a detailed and dedicated evaluation of vestibulo-ocular function in patients with SCA27B, and to develop a practical diagnostic framework that highlights the most prevalent findings and their anatomical correlates.We retrospectively analyzed 20 patients with genetically confirmed SCA27B who underwent structured bedside and quantitative neuro-visual assessments, including video-oculography (VOG) and video head impulse testing (vHIT). All patients exhibited cerebellar ocular motor abnormalities, including downbeat, gaze-evoked, and rebound nystagmus. Quantitative vHIT revealed bilateral vestibular hypofunction, most pronounced in the posterior canals (mean gain: 0.44), followed by anterior (0.54) and horizontal canals (0.83; p < 0.001). Brain MRI was normal in two-thirds of patients, and SARA scores indicated only mild ataxia, underscoring the diagnostic limitations of conventional tools. Based on our results, we developed a bedside diagnostic framework that anatomically links eye movement and vestibular signs to specific cerebellar structures, providing a clinically useful tool for early recognition of SCA27B. Our results emphasize the value of oculovestibular evaluation as a sensitive disease marker and support its integration into future composite diagnostic scales for cerebellar ataxias. Trial Registration Information : Not applicable (retrospective study)