vHIT Atlas

Acute vestibular syndrome

The acute vestibular syndrome (AVS) is defined as continuous vertigo or dizziness lasting more than 24 hours, with nausea or vomiting, gait instability, head-motion intolerance, and nystagmus^{[Tarnutzer AA 2011]}. The clinically critical question is the same in every case: is this a peripheral vestibulopathy (vestibular neuritis or labyrinthitis) or a posterior- circulation stroke? The two share much of their presentation, and the cost of missing a stroke is high.

Why MRI alone isn't the answer

It might seem that MRI should be the default workup for AVS, but diffusion-weighted imaging in the first 24–48 hours misses around 12% of small posterior-fossa strokes^{[Kattah JC 2009]}. A negative MRI in the first day does not exclude stroke, and the false reassurance can lead to a missed diagnosis. HINTS was developed precisely to outperform early MRI in this setting^{[Kattah JC 2009]}.

HINTS: the three-step bedside examination

Kattah and colleagues in 2009 published the prospective study that defined the modern HINTS examination^{[Kattah JC 2009]}. The three steps:

Head Impulse: a normal head impulse to both sides in a patient with continuous AVS is a central sign. Peripheral neuritis produces an abnormal HIT on the affected side; PICA stroke leaves the labyrinth intact and the HIT remains normal. Normal HIT in AVS = central.
Nystagmus: direction-changing horizontal nystagmus on lateral gaze is a central sign. Peripheral nystagmus obeys Alexander's law — it intensifies when looking in the direction of its fast phase but does not change direction. Central nystagmus can beat one way on right gaze and the other way on left gaze. Direction-changing nystagmus = central.
Test of Skew: vertical misalignment on the alternate cover test, due to imbalance of the otolith-ocular pathway, is a central sign in this context. Skew can occur peripherally but is rare; in AVS it is much more often central. Skew = central (in AVS).

Any one of these three being central is sufficient to call the syndrome central. The mnemonic that captures the rule for sending patients to imaging is INFARCT: Impulse Normal, Fast-phase Alternating, Refixation on Cover Test.

HINTS performance in trained hands

The original Kattah series (101 patients with AVS plus stroke risk factors) reported HINTS sensitivity of 100% and specificity of 96% for stroke when applied by trained neuro- otologists within 72 hours of symptom onset^{[Kattah JC 2009]}. This out- performed early diffusion-weighted MRI, which had sensitivity of approximately 88% in the first 24–48 hours.

HINTS-plus: adding hearing

A weakness of the original HINTS is that AICA strokes involving the labyrinthine artery produce peripheral-pattern HIT plus unilateral hearing loss. They can look completely peripheral on HINTS alone. The fix is HINTS-plus: a brief bedside assessment of hearing (rubbing fingers next to each ear, or formal audiometry where available) added to the three HINTS steps. A new unilateral hearing loss in a patient with AVS is a central sign and mandates imaging^{[Newman-Toker DE 2013]}.

HINTS sensitivity drops in untrained hands

The 100% sensitivity figure came from trained neuro-otologists. In emergency physicians without specific training, HINTS sensitivity is substantially lower — multiple studies suggest sensitivity in the 60–80% range. The implication: HINTS is a deceptively easy- looking test that requires specific training to perform reliably. Training emergency physicians to perform and interpret HINTS is increasingly seen as a high-value educational intervention.

When NOT to use HINTS

HINTS is validated for AVS — continuous vertigo with the full peripheral-syndrome features present at the time of examination. It is not validated for episodic vertigo (used for posterior-circulation TIA), for positional vertigo, or for chronic dizziness. Applying HINTS outside its target syndrome and acting on the result is unsound. A patient with intermittent vertigo and currently no nystagmus or HIT findings cannot be HINTS-ruled-out for stroke; if the suspicion is intermittent posterior-circulation ischaemia, image.

The ABCD2 problem

Newman-Toker and colleagues showed that HINTS outperforms ABCD2 (the standard TIA-stratification score) for screening AVS patients for stroke^{[Newman-Toker DE 2013]}. ABCD2 was designed for TIA, not AVS, and uses age, blood pressure, focal weakness, duration, and diabetes — all of which can be present in vestibular neuritis patients too. Relying on ABCD2 for AVS triage misclassifies neuritis patients as "stroke risk" (driving up imaging rates) and stroke patients as "low risk" (driving up missed-stroke rates). For AVS specifically, use HINTS-plus.

The unidirectional nystagmus trap

Spontaneous nystagmus in vestibular neuritis is horizontal-torsional, beats away from the affected ear, and intensifies on gaze in the direction of the fast phase (Alexander's law). This is fundamentally unidirectional— it doesn't change direction. Central lesions can produce nystagmus that looks at first glance like a peripheral pattern, but on careful gaze testing the direction reverses. Quick lateral-gaze testing can be done in the moment: ask the patient to look 30° right, hold for five seconds, observe; then 30° left, hold, observe. If the fast phase direction changes, the lesion is central^{[Chen L 2014]}.

vHIT in the emergency department

A portable vHIT machine in the emergency department transforms HINTS from a clinical impression into a quantitative test. Quantitative HIT obtained by vHIT in a vertigo patient objectively answers the question "is the HIT abnormal?" — removing the inter-rater variability that limits bedside HIT in untrained hands. In settings where this technology is available, vHIT-augmented HINTS achieves sensitivity comparable to expert neuro-otology assessment, even when performed by emergency physicians.

Practical algorithm

For the patient with acute vestibular syndrome:

Confirm the syndrome: continuous spontaneous vertigo with nystagmus, present at the time of examination.
Perform HINTS-plus: bedside head impulse (or vHIT if available), gaze-evoked nystagmus, alternate cover test, finger-rub hearing.
Apply INFARCT: any of Impulse-Normal, Fast-phase-alternating, Refixation-on-cover, or new hearing loss → central. Image urgently.
If all four are peripheral-pattern (abnormal HIT on the affected side, unidirectional nystagmus, no skew, no hearing loss): vestibular neuritis is the diagnosis. Treat symptomatically and arrange follow-up. Image only if other features warrant it.

Key teaching points

HINTS is for acute vestibular syndrome only; not for episodic or positional vertigo.
INFARCT mnemonic: Impulse Normal, Fast-phase Alternating, Refixation on Cover Test = central.
Add bedside hearing (HINTS-plus): new unilateral hearing loss in AVS = AICA stroke until imaging proves otherwise.
HINTS in trained hands outperforms early MRI; in untrained hands, sensitivity drops substantially.
Available vHIT removes most of the bedside-HIT subjectivity and improves emergency-department triage.

HINTS and acute vestibular syndrome