The video head impulse test: an aid to the diagnosis of spinocerebellar ataxias
Reviewed by Victor Osei-Lah

Spinocerebellar and Friedreich ataxias (SCA and FA) by their nature present in neuro-otology clinics. The diagnosis is ultimately genetic but the authors investigated the characteristics of the VOR using the video head impulse test (vHIT) in order to distinguish between the most common SCAs (1, 2 and 3) and FA. Twenty-three subjects were recruited as follows: 15 with SCA 3, four with SCA 2, four with SCA 1 and nine with FA compared to 40 healthy adult controls. They were subjected to horizontal vHIT. Disease severity was assessed with the Scale for the Assessment and Rating of Ataxia (SARA). The VOR gain dynamics were determined at median points after the onset of the head thrust (VOR40, VOR60 and VOR80). Other parameters analysed were VOR latency, gain below mean, asymmetry and characteristics of covert and overt saccades. Compared to controls, bilateral VOR deficits were recorded in FA and SCA3 but not in SCA2. There were many parameters to analyse making the presentation of a summary here challenging. However it is worth noting the following: VOR latency was increased in FA and SCA3 but normal in SCA2 and SCA1. In both FA and SCA3, VOR gain was low, being normal in the others. VOR dynamics distinguished between FA and SCA showing an increase in the former but not the latter. In all four groups, overt saccades were present but covert saccades were absent in all but SCA3. The site of lesion is thought to be central cerebellar flocculus dysfunction and the absence of covert saccades suggests saccadic suppression is not responsible for the oscillopsia experienced by these patients. A table depicts the main findings which used in combination may serve as ‘phenotypic hallmarks of the ataxias to orient genetic diagnosis’, the authors argue. The study also showed a negative correlation between VOR gain and SARA scores prompting the authors to suggest that VOR gain may be used as a neurophysiologic marker for disease severity. It would be interesting to see what the distinguishing features of the vertical canals might have added to diagnosis. This study is a useful addition to diagnostic accuracy but the authors accept that ultimately molecular genetics will remain the main diagnostic tool.

Vestibulo-ocular reflex dynamics with head-impulses discriminates spinocerebellar ataxias types 1, 2 and 3 and Friedreich ataxia.
Luis L, Costa J, Muñoz E, et al.
JOURNAL OF VESTIBULAR RESEARCH
2016;26:327-34.