Insights on different analysis techniques in the monothermal and bithermal caloric test – which parameter should we use to quantify vestibular function?

Abstract

Objective: To investigate the use of maximum slow component velocity (MSCV) and time-constant duration (TC_d) of elicited nystagmus in quantifying the caloric response and to assess the efficacy of these parameters in the monothermal screening test. Design: Retrospective analysis of caloric results obtained from 150 patients. Bithermal unilateral weakness (UW), directional preponderance (DP), monothermal caloric asymmetry (MCA) based on warm or cool irrigations only, were calculated using both MSCV and TC_d. Study sample: 66 males and 84 females, aged 16–88 years (μ = 50, σ = 17), who underwent vestibular assessment. Results: The correlation-coefficient between bithermal caloric unilateral weaknesses calculated using either MSCV or TC_d is 0.155 (p < 0.01). Using MSCV and setting significant MCA at 10%, the sensitivity and specificity were respectively 100% and 34% for monothermal warm and 82% and 53% for monothermal cool tests. Using TC_d and setting significant MCA at 5%, the sensitivity and specificity were respectively 90% and 77% for monothermal warm and 100% and 74% for monothermal cool tests. Conclusions: In the monothermal warm caloric test, MSCV can be used more reliably than monothermal cool to predict normal bithermal caloric response. The reverse is true if using TC_d. Unilateral-weakness calculated using TC_d and MSCV were poorly correlated and therefore likely to be demonstrating different aspects of vestibular function.

Key Words:

• Anatomy & physiology
• instrumentation
• medical audiology
• vestibular