The two otolith organs (the saccule and utricle) are positioned perpendicular to each other and sense linear acceleration, head tilt, and gravity, with the primary role of providing input to the vestibulospinal reflex for postural stability. The vestibulospinal reflex serves to modulate posture via two descending pathways that aid in tonic contractions of the antigravity muscles in the arms and legs (lateral vestibulospinal tract) and activate neck motoneurons for the coordination of neck and eye movements (medial vestibulospinal tract). The lateral vestibulospinal tract receives the majority of its input from the otoliths and the cerebellum, whereas the medial vestibulospinal tract receives the majority of its input from the semicircular canals.

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Background: Vestibular function (specifically, horizontal semicircular canal function) can be assessed across a broad frequency range using several different techniques. The head impulse test is a qualitative test of horizontal semicircular canal function that can be completed at bedside. Recently, a new instrument (video head impulse test [vHIT]) has been developed to provide an objective assessment to the clinical test. Questions persist regarding how this test may be used in the overall vestibular test battery. Purpose: The purpose of this case report is to describe vestibular test results (vHIT, rotational testing, vestibular evoked myogenic potentials, and balance and gait performance) in an individual with a 100% unilateral caloric weakness who was asymptomatic for dizziness, vertigo or imbalance. Data Collection and/or Analysis: Comprehensive assessment was completed to evaluate vestibular function. Caloric irrigations, rotary chair testing, vHIT, and vestibular evoked myogenic potentials were completed. Results: A 100% left-sided unilateral caloric weakness was observed in an asymptomatic individual. vHIT produced normal gain with covert saccades. Conclusions: This case demonstrates the clinical usefulness of vHIT as a diagnostic tool and indicator of vestibular compensation and functional status.