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LESSON 154

The head impulse test and HINTS

Year 2
Spring semester
Vestibular Assessment I
Vestibular assessment
Duration: 13:14

This lesson covers the bedside head impulse test, what a corrective saccade means, and the HINTS exam, which helps separate central from peripheral causes in the acute vestibular syndrome. We go through the head impulse, nystagmus and test of skew components, the HINTS plus approach, the evidence and the limitations.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will learn the bedside head impulse test and what a corrective saccade tells us.
Then we will cover the HINTS exam, which helps separate central from peripheral causes: head impulse, nystagmus and test of skew.
The head impulse test is a bedside test that examines each side of the vestibulo-ocular reflex, or VOR, separately.
In the graph, the navy line shows head velocity during a fast head impulse.
With an intact VOR, the eyes turn at almost the head's speed in the opposite direction; the blue dashed line follows the head curve.
On the weak side, eye velocity lags far behind the head, and gaze slips off the target.
The patient makes a fast eye movement to regain the target; this is called a corrective saccade.
The video head impulse test measures these curves; at the bedside, we only watch the eyes with the naked eye.
Before starting, ask whether the patient has neck pain, previous neck surgery or a problem with the neck vessels.
The patient looks at the nose of the examiner sitting opposite and keeps gaze on this target.
The head is held with both hands and turned very quickly to one side through a small angle of about ten to twenty degrees.
The direction and timing of the impulse are varied so the patient cannot predict them; a predicted impulse spoils the result.
As soon as the impulse ends, the examiner watches the eyes for a saccade back to the target.
Several impulses are made in each direction, and the finding is recorded together with the impulse direction in which the saccade appeared.
At the bedside, we meet three possible findings.
If the eyes stay on the target throughout the head impulse, the VOR in that direction is working adequately.
If the eyes jump back to the target after the head stops, this is an overt saccade.
The weak side is the side toward which the head was turned; for example, a saccade on rightward impulses means the right VOR is weak.
Some saccades, however, appear while the head is still moving; these are called covert saccades.
Because covert saccades cannot be seen with the naked eye, the bedside test may miss partial or compensated losses.
In patients with serious neck problems, the test is done only after a joint decision with a physician, and with great care.
The patient must not blink and must keep gaze on the target for the saccade to be interpreted correctly.
If the impulse is not fast enough, the visual pursuit system takes over and a weak side may look normal.
The bedside test is reliable in marked losses, but its sensitivity is low in mild or compensated losses.
Doubtful findings can be confirmed with the video head impulse test, or vHIT, which also shows covert saccades.
The acute vestibular syndrome is severe dizziness that begins suddenly and continues without a break.
The symptoms are not limited to hours; they usually last for days.
The patient has nausea, vomiting and complaints that worsen with head movement.
Examination often shows spontaneous nystagmus and unsteadiness when walking.
The most common cause of this picture is a peripheral problem such as vestibular neuritis.
However, the same picture can also be caused by a stroke affecting the brainstem or the cerebellum.
A stroke in the posterior circulation, especially in the cerebellum, can mimic vestibular neuritis very closely.
Some of these patients have no obvious neurological signs such as slurred speech, weakness or double vision.
So it is not always possible to make the distinction from the general neurological examination alone.
Diffusion-weighted MRI taken in the first hours and days may fail to show some small brainstem strokes.
CT is even more limited in showing small strokes in the posterior fossa.
This is where a bedside examination based on eye movements becomes a valuable guide.
HINTS is a three-step eye examination made up of the head impulse, nystagmus and test of skew.
In the first step, the head impulse test checks whether the VOR is working on that side.
In the second step, we look at whether the nystagmus changes with the direction of gaze.
In the third step, eye covering is used to look for vertical misalignment of the eyes, that is, skew deviation.
The examination takes a few minutes and needs no special equipment, but it does require experience.
Within HINTS, the interpretation of the head impulse test can seem reversed at first glance.
In vestibular neuritis the problem lies in the labyrinth or vestibular nerve, so impulses toward that side cause a corrective saccade.
So in the acute vestibular syndrome, an abnormal head impulse test fits a peripheral cause.
In most cerebellar or brainstem strokes, however, the labyrinth and nerve are intact and the VOR pathway is preserved.
So in a patient with continuous dizziness and nystagmus, a normal head impulse test suggests a central cause.
In this setting, a normal test is not reassuring; on the contrary, it is a finding that calls for attention.
In the second step, nystagmus is observed while the patient looks straight ahead, then to the right and to the left.
Peripheral nystagmus is unidirectional; it is horizontal and torsional and usually beats toward the healthy ear.
It increases when looking toward the fast phase and decreases when looking the other way; this is Alexander's law.
Nystagmus that beats right on right gaze and left on left gaze, however, is direction-changing gaze-evoked nystagmus.
Direction-changing gaze-evoked nystagmus, or purely vertical or purely torsional nystagmus, suggests a central cause.
However, in some central lesions the nystagmus can also be unidirectional, so this sign alone is not enough.
The test of skew is done with the alternate cover test.
While the patient looks straight ahead, the examiner covers one eye with a hand, then quickly covers the other eye.
The examiner watches whether the uncovered eye makes an upward or downward correction to regain the target.
A vertical correction shows that the vertical alignment of the two eyes is disturbed, that is, a skew deviation.
Skew deviation arises when the brainstem pathway carrying gravity information from the otolith organs is disrupted.
Because it is rare in peripheral losses, its presence in the acute vestibular syndrome suggests a central cause.
Now let us put the three components together.
In the peripheral pattern the head impulse test is abnormal; in the central pattern it is normal.
Peripheral nystagmus is unidirectional; in the central pattern it may change direction with gaze.
There is no skew deviation in the peripheral pattern; its presence is a central sign.
All three components must fit the peripheral pattern; even a single central finding suggests a central cause.
The last row added to the table is new-onset hearing loss; we will explain it shortly.
New-onset hearing loss together with acute dizziness is a fourth component added to HINTS.
The labyrinthine artery of the inner ear usually arises from the anterior inferior cerebellar artery, or AICA.
A stroke affecting this vessel can also involve the labyrinth, so the head impulse test may be abnormal, as in a peripheral loss.
So a simple bedside hearing check, such as finger rubbing, is added; this approach is called HINTS plus.
New hearing loss together with the acute vestibular syndrome also calls for urgent assessment because of the possibility of stroke.
The key study showing the value of HINTS is the one by Kattah and colleagues in 2009, with one hundred one patients.
In this study, HINTS identified strokes with one hundred percent sensitivity and about ninety six percent specificity.
In the same patients, the initial diffusion MRI did not show eight strokes that were confirmed later.
However, the study was done in patients at high stroke risk, with the examination performed by an experienced neuro-ophthalmologist.
Later studies showed that accuracy can drop markedly when the examination is done by people without adequate training.
HINTS is not a test to be applied to every patient with dizziness.
It is meaningful only in patients whose dizziness began acutely, is continuous and is still present during the examination.
Spontaneous nystagmus must be present during the examination; without nystagmus, the head impulse result can be misleading.
HINTS is not used for brief attacks when turning in bed or for episodes that come and go; here, positional tests and the history come first.
Gait examination also matters; a patient who cannot stand even with help needs urgent assessment, whatever the HINTS result.
HINTS is not a diagnostic tool but a bedside examination that supports the decision on urgent referral.
The audiologist's task in this process is not to make a diagnosis but to observe accurately and refer at the right time.
In a patient with acute dizziness, the direction of nystagmus, its change with gaze and the head impulse finding are carefully observed.
If possible, eye movements are recorded with video goggles; the recording makes the physician's assessment easier.
If even one finding suggests a central pattern, the planned test battery is put on hold.
The patient is referred without delay for urgent medical assessment, with a short, clear summary of the findings.
A clinical tip: in a patient with acute, continuous dizziness, do not read a normal head impulse test as good news.
In this setting, a normal head impulse is a finding that brings a central cause to mind.
Even one of direction-changing nystagmus, skew deviation or new hearing loss is enough for urgent referral.
Record the findings together with the time of onset; timing is critical information for the emergency team.
In the head impulse test, a corrective saccade shows that the VOR is weak on the side of the impulse.
HINTS consists of the head impulse, nystagmus and test of skew; HINTS plus also asks about new hearing loss.
A normal head impulse, direction-changing nystagmus or skew deviation suggests a central cause.
HINTS is meaningful only in patients with acute, continuous dizziness and nystagmus, and it requires training.
Test yourself: in a patient with acute, continuous dizziness, which finding suggests a central cause?
The correct answer is C: a normal head impulse test.
In a peripheral loss the head impulse is abnormal; in most strokes the VOR pathway stays intact, so the test is normal.
In the next lesson we will learn the positional tests, namely the Dix-Hallpike maneuver and the supine roll test.
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