I was recently reading an article titled Evaluating the Diagnostic Accuracy of the Head Impulse Test- A Scoping Review. This article’s primary aim was to assess the ability of the video head impulse test (vHIT) to detect vestibular dysfunction based on an extensive review of the literature.
In recent years, the introduction of different assessment techniques has allowed for more comprehensive assessment of the vestibular system. This has left many clinics wondering what tests they should complete to best identify vestibular disorders. Correct identification of the cause of cause of ones symptoms is paramount to reaching a diagnosis and appropriate treatment.
Vestibular disorders generally result in impairment of the vestibular ocular reflex (VOR) and vestibular spinal reflex (VSR). The primary function of the VOR is to provide visual stability with head movement and the primary function of the VSR is to allow for reflexive postural control in order to stay upright. The vestibular system primarily senses head acceleration and impairment of these reflexes can result in symptoms of vertigo, disequilibrium, disorientation with head movement, as well as nausea and vomiting to name but a few.
Traditionally and still the case in the majority of clinical environments, assessment of the vestibular system is completed with caloric irrigations, which evaluates the low frequency (slow speed of head movement) VOR. This assessment protocol introduces temperature change to the ear by putting warm and cool air or water into the ear canal, causing a change in the temperature of the inner ear fluids. The patient is reclined at a 30-degree angle for this test and the resulting change in density causes the inner ear fluids either to rise or sink, primarily stimulating the horizontal semicircular canal (horizontal head turn sensor) at an extremely low frequency. This creates a horizontal nystagmus (jerking eye movement) and allows for measurement of the vestibular ocular reflex from each ear independently. The responses from each side can then be compared to one another to determine if they are symmetric and of normal amplitude.
Caloric irrigation is currently the reference standard for detecting a unilateral vestibular deficit. This test protocol is rather invasive, time consuming, often uncomfortable for the patient, and can occasionally evoke nausea and vomiting. These factors have led many to look for faster, more comfortable, and functionally relevant means to assess VOR function.
The video head impulse test is one such method that is faster to complete and more comfortable for most patients. This method of assessment also allows for assessment of all of the semicircular canals (head turn sensors) rather than just the horizontal semicircular canal and at realistic speeds of head movement encountered in one’s every day life. This test utilizes a set of tightly fitting goggles that can measure the high frequency (high speed of head movement) VOR in response to impulsive head movements.
The traditional method requires the patient to focus on an earth fixed object while the clinician quickly moves their head in the plane of the semicircular canal pair that is being measured. The VOR response in a healthy individual will create an equal and opposite amount of eye movement to the head movement, allowing the patient to maintain focus on the earth fixed object. For someone with a vestibular deficit, a clinician would observe the eyes moving with the head rather than opposite the head and a corrective saccadic eye movement is required to re-fixate the eyes on the earth fixed object. This assessment technique does require the patient to have at least a somewhat mobile neck to achieve the appropriate head movement, as well as lightweight, tightly fitting goggles to decrease the likelihood of goggle slippage.
Results of the Scoping Review
In general, the majority of the studies showed a relatively low sensitivity, or limited ability to correctly detect those with a vestibular disorder. It seems this low sensitivity was most pronounced with certain vestibular diagnoses such as Meniere’s disease and vestibular migraine. The video head impulse test was better at correctly identifying diagnoses such as vestibular neuritis, bilateral vestibular hypofunction, or vestibular pathologies with greater degrees of caloric hypofunction (reduced caloric response).
So How Does vHIT fit in to the assessment protocol?
In my opinion, vHIT is simply a piece of the vestibular assessment protocol and cannot be directly compared to the caloric as they are really examining different things. The vHIT is a measure of high frequency VOR function while caloric irrigations are a measure of extremely low frequency VOR function. These measures are often complementary to one another.
Meniere’s Disease Vs. Vestibular Migraine
The video head impulse test can be very useful in helping differentiate Meniere’s disease from vestibular migraine, which can have several overlapping symptoms. In our practice, we have found that with repeated episodes of Meniere’s disease, one is likely to have at least some degree of caloric hypofunction, while most often having a normal vHIT. We also perform a hearing test on all patients with suspected Meniere’s disease, as the diagnosis according to the Barany Society requires documented low frequency sensorineural hearing loss. In general, the pattern of low frequency sensorineural hearing loss, caloric hypofunction and normal vHIT is helpful in reaching the diagnosis of Meniere’s disease. This pattern seems to be reflected in this scoping review as well. Most often vHIT, calorics, and hearing tests are normal for those with vestibular migraine.
Vestibular Neuritis/Labyrinthitis
Our findings in the daily clinical assessment of those with vestibular neuritis or labyrinthitis echo the findings of the scoping review. Most often, if a patient has a mildly reduced caloric response, we find a normal vHIT measure but if the patient has a larger caloric hypofunction, then often the vHIT is also abnormal. In cases of labyrinthitis the hearing test will also show some degree of sensorineural hearing loss.
That is assuming the patient is not acutely vertiginous. If a patient recently suffered the vestibular neuritis within days to weeks of assessment, or if they still have spontaneous nystagmus, then vHIT is frequently abnormal. In fact, an assessment called the HINTs is very effective in differentiating a potential brainstem stroke from a vestibular neuritis with an abnormal head impulse being strongly predictive of a peripheral vestibular abnormality.
Bilateral Vestibular Hypofunction
Those with bilateral vestibular hypofunction typically have abnormal vHIT measures in both directions in our experience, which is similar to what was reported in the scoping review.
vHIT in Benign Paroxysmal Positional Vertigo (BPPV)
BPPV is the most common vestibular disorder but was not mentioned in the review. This condition is due to particles (otoconia) within the inner ear migrating into one of the semicircular canals. This produces recurrent brief episodes of vertigo with head movement. If someone has BPPV related to another vestibular abnormality, then the results of vHIT are variable and depend on the underlying vestibular abnormality that caused the individual to develop BPPV. Most individuals with BPPV develop the condition as a natural part of the aging process and this is an otherwise mostly healthy vestibular system sensing abnormal fluid motion due to the otoconia moving when the individuals moves their head. In this scenario vHIT should be normal.
vHIT is a piece of the puzzle
The video head impulse test is a useful and complementary part of a comprehensive vestibular evaluation. This measure can be extremely helpful in separating Meniere’s disease, vestibular migraine, and vestibular neuritis/labyrinthitis from one another due to the different pattern of testing findings observed with these conditions.
Currently the literature would suggest that if someone has an abnormal vHIT, then a diagnosis of a peripheral disorder can be made but if one’s vHIT is normal then additional assessment, including caloric irrigations are most likely warranted.
* featured image courtesy Boys Town & Micromedical Technologies,
