Comparison of Vestibular Autorotation and Caloric Testing

Abstract

The two most common stimuli of the vestibular system for diagnostic purposes are caloric and rotational head movements. Caloric stimulation, by delivering thermal energy to the lateral semicircular canal, is a well-studied method of vestibular testing, and its clinical usefulness has been established. Vestibular autorotation testing uses high-frequency (2 to 6 Hz), active head movements to stimulate the horizontal and vertical vestibulo-ocular reflex to produce measurable eye movements that can be used to calculate gain and phase. We compared the alternate bilateral bithermal caloric results with the vestibular autorotation test results obtained from 39 patients with peripheral vestibular disorders and from 10 patients with acoustic neuroma. In the peripheral disorder group, only 2 of 14 patients with equal caloric response (<20% reduced vestibular response) had a normal vestibular autorotation test result. No patients with a reduced vestibular response greater than 21% had a normal vestibular autorotation test result. In the acoustic neuroma group, four patients had a normal reduced vestibular response, but all patients had an abnormal vestibular autorotation test result. We conclude that testing both the horizontal and vertical vestibulo-ocular reflexes in their physiologic frequency range with the vestibular autorotation test provides additional information that could be missed by conventional caloric testing. Therefore high-frequency rotational testing is a valuable addition to the vestibular test battery.