Comparison of Suppression Head Impulse and Conventional Head Impulse Test Protocols

Roh, Kyung Jin; Kim, Ju Young; Son, Eun Jin

Abstract

OBJECTIVES
The head impulse test paradigm (HIMP) assesses semicircular canal function by measuring compensatory saccades during head movements as an indication of an impaired vestibulo-ocular reflex (VOR). The recently introduced suppression head impulse test paradigm (SHIMP) examines anticompensatory saccades after head movements as a measure of intact VOR. Thus, HIMP measures a decrease in vestibular function, whereas SHIMP measures residual function. We evaluated the effectiveness of SHIMP, compared HIMP and SHIMP results in the same subjects, and examined the relationship between the 2 tests.
METHODS
HIMP and SHIMP protocols were performed in 73 patients. The patients were instructed to maintain their gaze on a fixed target for the HIMP, or a moving target for the SHIMP during head impulses. The VOR gain and saccade parameters were compared.
RESULTS
HIMP and SHIMP data were obtained for all ears except in 3 patients. The VOR gain with SHIMP was smaller than for HIMP, but showed significant correlation (r=0.8356, p<0.001) and substantial agreement (k=0.79). However, neither the percentage of saccades (appearance of HIMP compensatory saccades and reduction of SHIMP anticompensatory saccades) nor their amplitudes were correlated between the 2 tests.
CONCLUSIONS
The HIMP and SHIMP protocols are valuable tools to evaluate VOR during high-velocity head movements. Our results confirm their agreement as measures of VOR gain during head impulses, but also show that the relationship between compensatory and anticompensatory saccades is not straightforward. Thus, care should be taken during clinical interpretation of either protocol.