Episodic Vestibular Syndrome with Hyperventilation-Induced Downbeat Nystagmus.

Hyperventilation-induced downbeat nystagmus (HV-DBN) has been reported in cerebellar disorders and explained by a loss of the inhibitory cerebellar output via a metabolic effect on cerebellar Ca2+ channels. The aim of this study was to determine the clinical characteristics and underlying pathogenesis of episodic vestibular syndrome (EVS) with HV-DBN. Of 667 patients with EVS, we recruited 22 with HV-DBN and assessed their clinical characteristics, video-oculographic findings, and the results of molecular genetic analyses. The age at symptom onset was 47.5 ± 13.0 years (mean ± SD), and there was a female preponderance (n = 15, 68%). The duration of vertigo/dizziness attacks ranged from minutes to a few days, and 11 patients (50%) fulfilled the diagnostic criteria for vestibular migraine. HV-induced new-onset DBN in 8 patients, while the remaining 14 showed augmentation of spontaneous DBN by HV. The maximum slow-phase velocity of HV-DBN ranged from 2.2 to 11.9°/s, which showed a statistical difference with that of spontaneous DBN (median = 4.95, IQR = 3.68-6.55 vs. median = 1.25, IQR = 0.20-2.15, p < 0.001). HV-DBN was either purely downbeat (n = 11) or accompanied with small horizontal components (n = 11). Other neuro-otologic findings included perverted head-shaking nystagmus (n = 11), central positional nystagmus (n = 7), saccadic pursuit (n = 3), and horizontal gaze-evoked nystagmus (n = 1). Gene expression profiling with a bioinformatics analysis identified 43 upregulated and 49 downregulated differentially expressed genes (DEGs) in patients with EVS and HV-DBN and revealed that the downregulated DEGs were significantly enriched in terms related to the ribosome pathway. Our results suggest that the underlying cerebellar dysfunction would be responsible for paroxysmal attacks of vertigo in patients with EVS and HV-DBN.