From the Guidelines
A caloric test is considered asymmetric when there is a difference of 25% or greater between the vestibular responses of the right and left ears. This threshold is crucial in identifying unilateral vestibular hypofunction, which may indicate pathology on the weaker responding side. The calculation of this percentage is typically done using Jongkees' formula, comparing the slow-phase eye movement velocities elicited from each ear during warm and cool water or air stimulation.
When interpreting caloric test results, it's essential to consider the potential impact of various factors, such as:
- Inadequate irrigation technique
- Middle ear pathology
- Patient alertness
These factors can affect the reliability of the test results. However, the 25% cutoff has been established through clinical research as the point where normal physiological asymmetry ends and pathological differences begin, accounting for natural variability between ears in healthy individuals 1.
Key points to consider in the context of caloric test asymmetry include:
- The importance of using a standardized method, such as Jongkees' formula, for calculating asymmetry
- The need to interpret caloric test results in conjunction with other clinical findings
- The potential for factors like middle ear pathology or patient alertness to influence test results, as noted in guidelines for conditions like Ménière's disease 1
From the Research
Caloric Test Asymmetry
- The percentage of asymmetry to consider caloric tests asymmetric is not universally defined, but a study published in 2021 2 used a cutoff point of 25% asymmetry to differentiate between patients with significant and non-significant improvement in Dizziness Handicap Inventory scores.
- This study found that patients with more than 25% asymmetry had no significant improvement in Dizziness Handicap Inventory scores, whereas those with less than 25% asymmetry had significant improvement in functional domain scores.
- Another study published in 2008 3 noted that caloric testing reference values may vary according to each unit, and the cutoff point is defined based on local studies.
Factors Influencing Caloric Test Results
- Age can be a factor in caloric test results, with older subjects showing greater intersubject variability 4.
- The type of dizziness can also influence the vestibular caloric test result, with vertigo associated with tinnitus and/or hearing loss being more frequent in caloric tests with peripheral abnormality 5.
- Electronystagmographical analysis of caloric test parameters can help in the evaluation and diagnosis of vestibular disorders, with different patterns of nystagmus observed in peripheral and central vestibular lesions 6.
Test Reliability and Repeatability
- The reproducibility of caloric tests of vestibular function has been evaluated in young and old subjects, with reasonably reliable test-retest repeatability over time in both age groups 4.
- However, intersubject variability was statistically significant in both age groups, highlighting the importance of establishing a vestibular caloric response baseline for each subject.