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High-frequency vestibulo-ocular reflex (VOR) evaluation in patients with spontaneous downbeat nystagmus: a
T J Odorico1, J L De La Fuente2, F G Urbina2
1Department of Neurology, Hospital César Milstein, Buenos Aires, Argentina. teo.odorico@gmail.com.
Introduction:
Spontaneous downbeat nystagmus (DBN) is generally attributed to vestibulocerebellar dysfunction, although its exact pathophysiological mechanism remains unclear. The video head impulse test (vHIT) quantifies vestibulo-ocular reflex (VOR) gain in semicircular canals, allowing evaluation of VOR imbalance.
Objective:
To elucidate the role of VOR in spontaneous DBN of central origin we measured gain across semicircular canals and gain asymmetry between coplanar canals, compared with matched healthy subjects.
Methods:
Nested case-control study within a retrospective cohort. We included 30 patients with DBN and 30 healthy controls matched for age and sex. Gains of the right horizontal (RH), left horizontal (LH), left anterior (LA), right posterior (RP), right anterior (RA), and left posterior (LP) canals were analyzed, together with horizontal (RH-LH) and vertical (LA-RP and RA-LP) gain asymmetry. Mann-Whitney U test was used for all comparisons (α = 0.05).
Results:
Cases showed significantly lower gains in the RH (p = 0.009), LH (p = 0.002), RP (p = 0.004), and LP (p = 0.016) canals, and a significantly higher gain in the RA canal (p = 0.002). The LA canal showed no significant difference. The LARP (p < 0.001) and RALP (p < 0.001) asymmetries were significantly greater in cases.
Conclusions:
Patients with DBN showed a pattern of VOR impairment characterized by hypofunction of the horizontal and posterior canals, hyperfunction of the anterior canals, and marked asymmetries in the vertical LARP and RALP planes. These findings are preliminarily consistent with the hypothesis of asymmetric cerebellar modulation of the VOR.
