PP1406 - Clinical Utility of a Caloric Perception Threshold in Patients with Postural Instability

Abstract:
This pilot investigation compared behavioral measures of caloric perception to postural stability tasks that required vestibular cues to maintain balance. Subjects were recruited from a specialized dizzy clinic and enrolled if they reported symptoms of dizziness and/or imbalance but were found to have normal vestibular testing. Temporal characteristics of caloric perception were collected using a response button and used to define a perceptual threshold. Postural stability was assessed using equilibrium scores from condition 5 of the sensory organization test (SOT), which was compared to caloric perception. Behavioral measures of caloric perception may be useful in identifying patients with abnormal motion perception.

Summary:
Postural instability and falls are commonly reported in patients referred for vestibular function testing related to dizziness and/or imbalance. Yet, in some patients, vestibular testing is normal. Recent evidence has suggested that postural instability may be related to altered self-motion perception of vestibular cues, a phenomenon known as vestibular agnosia or neglect. The absence of self-motion perception during the caloric exam has been shown to result in a greater occurrence of falls on tests of functional balance. Few research investigations have examined caloric perception beyond binary yes or no responses. The purpose of this prospective study was to compare behavioral measures of caloric perception to postural stability in adults with normal vestibular testing. Subjects were part of an unselected group of clinical patients referred for routine vestibular function testing. Subjects were included if they had normal peripheral and central vestibular function based on the following assessments: videonystagmography (VNG) including caloric testing, rotary chair, video head impulse testing (vHIT), and vestibular evoked myogenic potentials (VEMPs). Patients were excluded if they reported a history of peripheral neuropathy, significant musculoskeletal diagnoses, or if their slow-phase velocity during caloric testing was less than 15 degrees/second.

Caloric perception was measured using a custom MATLAB program and a three-button response keypad. During a 30-second warm caloric irrigation, patients were asked to press and hold the keypad if they felt an increase or decrease in self-motion perception. They were also asked to press the button as soon as the sensation went away. From these button presses, perception onset time relative to the magnitude of their corresponding slow-phase velocity was tabulated and used to define a caloric perception threshold. The starting ear was counterbalanced to account for novelty effects. The SOT was then administered on all patients to assess postural stability, specifically results from their equilibrium score on condition 5, which evaluates how well vestibular cues are utilized to maintain balance.

Data collection is ongoing. However, we hypothesize that patients with caloric perception thresholds that exceed our normative cutoff will also have greater postural sway on condition 5 of the SOT. Behavioral measures of caloric perception may provide a useful clinical tool to accurately and reliably measure motion perception during routine vestibular testing.