Vestibular asymmetry in caloric and video head impulse testing: Do we interpret it correctly?

Area of Science:

• Vestibular diagnostics
• Neuroscience
• Ophthalmology

Background:

• Jongkees' formula (JF) is widely used for vestibular asymmetry quantification in caloric and video head impulse tests (vHITs).
• JF calculates unilateral weakness (UW) using the stronger ear (SE) and weaker ear (WE) responses.
• However, JF's interpretation can be misleading for clinicians regarding the percentage of weakness.

Purpose of the Study:

• To mathematically analyze the information provided by Jongkees' formula (JF).
• To explore alternative, more meaningful equations for assessing vestibular asymmetry in vHITs and caloric tests.
• To address the limitations of JF in accurately reflecting unilateral weakness.

Main Methods:

• Mathematical analysis of Jongkees' formula (JF).
• Comparison of JF with alternative linear and direct asymmetry calculations.
• Evaluation of formula performance in scenarios with unilateral and bilateral vestibular deficits.

Main Results:

• Jongkees' formula (JF) has three key limitations: nonlinear underestimation of paresis, calculation based on an average rather than direct weakness, and inflated values in bilateral deficits.
• Alternative linear calculations do not fully resolve JF's limitations.
• For vHITs, using head velocity and an ideal gain of 1 allows for a simple side-to-side gain difference, avoiding inflated results and simplifying clinical interpretation.

Conclusions:

• Jongkees' formula (JF) provides an unwieldy and potentially misleading measure of unilateral weakness.
• Alternative methods, particularly a simple side-to-side gain difference for vHITs, offer more accurate and clinically intuitive assessments of vestibular asymmetry.
• Revised calculations are crucial for precise vestibular diagnostics.