Objective:

This study investigates the otolith-ocular function in patients with spinocerebellar ataxia 27B (SCA 27B) using video ocular counter-roll (VOCR) test. 

Background:

Spinocerebellar ataxia27B (SCA27B) is a recently recognized yet relatively common form of cerebellar ataxia. Patients often present with dizziness and imbalance, and recent studies have identified vestibular hypofunction with marked impairment of semicircular canal function. However, the contribution of the otolith system —the other key component of vestibular function— remains unknown in SCA27B.  In this study, we examined otolith-ocular function using vOCR test in patients with SCA 27B. By characterizing this previously unexplored aspect of vestibular involvement, we aim to refine understanding of the underlying vestibular pathology and support the development of diagnostic tools for more accurate clinical detection.  

Design/Methods:

VOCR results were obtained from patients with genetically confirmed SCA27B, along with video head impulse testing (vHIT) and clinical history. As part of routine clinical testing, vOCR was performed to evaluate otolith function and vHIT to evaluate semicircular canal function. The vOCR test was performed with 30° en-block lateral tilt of the head and body to each side. The vOCR value was quantified as the difference in ocular torsion between the upright head position and the static head tilt (i.e., ocular counter-roll).

Results:

SCA27B patients had reduced vOCR with average of 1.7° ±0.22°(SD).  Compared with the established normal value of 4.5° during a 30° head tilt, these results indicate a markedly reduced vOCR in patients with SCA27B. The vHIT results also revealed some gain reduction in the horizontal (0.78 ± 0.39), anterior (0.54± 0.28), and posterior (0.50±0.3) canals .   

Conclusions:

This study presents the first evidence of otolith pathway dysfunction in SCA27B, suggesting that otolith–ocular impairment may be more pronounced than canal deficits. Together, these results help define the vestibular profile of this disorder.