Vestibular Performance During High Acceleration Stimuli Correlates with Clinical Decline in SCA6

Abstract

Objective: To determine vestibular dysfunction and correlate ocular motor abnormalities with clinical parameters in patients with spinocerebellar ataxia type 6 (SCA6). Methods: We examined vestibular responses over a broad range of stimulus acceleration in 11 individuals with SCA6 (6 men, age range=33-72 years, mean age±SD=59±12 years) using bithermal caloric, rotary chair, and head impulse tests. Correlations were also pursued among disability scores, as measured using the International Cooperative Ataxia Rating Scale, disease duration, age at onset, CAG repeat length and ocular motor abnormalities including spontaneous, gaze-evoked, head-shaking and positional nystagmus, saccades, smooth pursuit and the gain (eye velocity/head velocity) of the vestibulo-ocular reflex (VOR). Results: In response to relatively low-acceleration, low-frequency rotational and bithermal caloric stimuli, VOR gains were normal or increased regardless of the disease severity. On the other hand, with relatively high-acceleration, high-frequency head impulses there was a relative increase in gain in the mildly affected patients and a decrease in gain in the more severely affected patients

therefore the gains were inversely correlated with the disease severity (Spearman correlation, R=-0.927, p<0.001). Smooth pursuit also deteriorated as the disease severity was increased. Conclusions: Selective decrease of the vestibular responses during high-acceleration, high-frequency stimuli may be ascribed to degeneration of either the flocculus or vestibular nuclei. The performance of the VOR during head impulses and smooth pursuit may be quantitative indicators of clinical decline in SCA6.