Correlation between caloric test results and VHIT VOR gains in unilateral horizontal canal deficits: a cross-sectional study.

The purpose of the study is to evaluate the correlation between caloric test results and video head impulse test (VHIT) vestibulo-ocular reflex (VOR) gains in unilateral horizontal canal deficits in order to define a possible threshold value above which caloric deficits should be associated with predictable low VHIT VOR gains. Caloric test and VHIT were realised in 105 patients presenting with symptoms of rotational vertigo occurring within the last 2 weeks. The authors defined the cutoff value for a caloric abnormality as more than 15% of canal deficit, which allowed us to divide our patients on groups based on the severity of their caloric asymmetry. Then, the authors performed the VHIT considering abnormal horizontal gain as less than 0.8 with catch-up saccades. The authors evaluated the prevalence of results dissociation between the two tests and the correlation between the caloric asymmetry and the horizontal VHIT VOR gains in each group according to the severity of canal deficit. The correlation was considered statistically significant if less than 0.05 (Fisher's exact test). The caloric test revealed a significant unilateral deficit in 50 patients (47.6%). The interval of deficit between 21 and 40% included 25 patients, 18 (72%) presenting with normal VHIT VOR gains versus 7. On the other hand, for the 12 patients in the intervals of 81-100% of deficit, the VHIT VOR gain was highly abnormal in all cases. In comparison with the normal caloric test group, a correlation between each interval of caloric deficits and VHIT VOR gains has been assessed. This correlation was significant in the interval of 41-60% (=0.04 <0,05) and in the interval of 81-99% next to patients with a total deficit of 100% (=0.006 <0.05 for each). It appears that simultaneous affection of high vestibular frequencies evaluated on VHIT may be more likely and predictable above a minimal threshold of 40% caloric asymmetry, with better discrimination between normal and abnormal VHIT above 80%. Thus, they are two complementary tests to use as a couple rather than a replacement one for the other.