Why is it important to alert the patient during vestibular testing?
Accurate measurement of the Vestibular-ocular reflex (VOR) is essential to diagnosing and managing neuro-vestibular disorders. Alerting the patient can seem counterintuitive since we are measuring a reflex and not something the patient is actively engaged in. This may be why some clinicians believe alerting is not always necessary when testing for vestibular nystagmus. Vestibular nystagmus is significantly suppressed at a cortical level, and this will ultimately affect interpretation measuring a significantly reduced nystagmus and, in the worst cases resulting in a missed diagnosis.
Nystagmus generated from the vestibular system has two components. A slow component (think eye drift) is generated from the vestibular system and brainstem. Secondly, a fast component is generated from a higher cortical level in which the eye makes a saccadic movement back towards the center, which is the VOR's primary function to stabilize vision. Continuous stimulation at the cortical level by alerting maintains the generation of the fast phase component of nystagmus and, therefore, accurate measurements during testing.
Which Tests should Clinician Alert the Patient?
Any Vestibular Tests that are performed in the absence of vision.
- Spontaneous nystagmus measurements;
- Vision Denied Gaze Tests;
- Head Shake, Head Heave, Ocular Counter Roll;
- Mastoid Vibration Test;
- Rotational Chair Testing;
- Positioning Tests for BPPV if clear nystagmus is not visible.
How to Alert the Patient?
Evidence shows that the task needs to be moderately tricky; otherwise, the alerting is not as effective as it should be, and what is difficult for some patients will not be difficult for others. It is also dependent on the type of test being undertaken. For example, a patient doing a vision-denied gaze test will need a more complex alerting task than a patient during a caloric test. Having a good repertoire of tasks available so the clinician can quickly switch once the task becomes too easy, complex, or redundant is a must.
Clinicians should be mindful of anxiety-inducing tasks, as anxiety can lead to artefactual eye movements affecting the VNG results. For example, unnecessarily complicated maths tasks ("count backward from 200 in 13s") are not comfortable tasks for many of the population. Additionally, the less anxious the patient is during specific tests such as the caloric, the less likely they are to suffer emesis.
A further tip is to find out what interests the patient. Do they like to cook? Or do they take a particular interest in cars/animals/sports? A topic of interest could be easily integrated into mental alerting tasks.
- Boys/Girls names that begin with the letter "D." (As soon as the patient struggles to think, change the letter);
- Animals from different continents;
- Breeds of dogs beginning with different letters;
- Street names from their local area;
- Reciting their favorite recipe;
- Naming family members in age order.
Sometimes, it may be necessary to task patients non-verbally, for example, if there is a language or communication barrier. Makowiec et al. (2021) found no significant difference between verbal and non-verbal alerting tasks on the rotary chair and caloric testing. The task they used was a braiding task. At the Hypatia clinic, we ask the patient to mold different shapes with plasticine.
To conclude, alerting tasks should be utilized appropriately throughout the vestibular test battery, and several factors should be considered when deciding how to task the patient. Effective tasking will lead to clearer, more accurate vestibular nystagmus measurements and more straightforward laboratory test interpretation.
Makowiec, K., Smith, K., Deeb, A., Bennett, E., & Sis, J. (2021). Influence of tasking during vestibular testing. American Journal of Audiology, 30(3), 755-760.
Resources for More Information
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