The HINTS test is a rapid, three-part bedside examination designed to help clinicians differentiate between central and peripheral causes of acute vestibular syndrome (AVS). AVS is characterized by acute onset of vertigo, nausea, vomiting, and gait instability. Performing the HINTS test accurately can significantly aid in identifying potentially life-threatening central etiologies, such as stroke, even in the presence of severe vertigo that might initially suggest a benign peripheral vestibular disorder.

The Head Impulse Test (HIT)

The first component of the HINTS battery is the Head Impulse test, sometimes referred to as the vestibulo-ocular reflex (VOR) gain test. To perform this, the examiner quickly and unpredictably rotates the patient's head approximately 10-20 degrees to one side while the patient maintains fixation on the examiner's nose. A normal, intact VOR allows the eyes to remain fixed on the target without corrective saccades. If the VOR is impaired (suggesting a peripheral lesion), the eyes will briefly move off the target and then snap back with a corrective saccade. An abnormal Head impulse test (presence of corrective saccades) typically points towards a peripheral vestibular lesion.

The Nystagmus Test

The second part of the assessment is the nystagmus test. Nystagmus refers to involuntary, rhythmic eye movements. In the HINTS examination, the patient is asked to look straight ahead, and then to gaze approximately 30 degrees to the left and right. The presence and characteristics of nystagmus are observed. Unidirectional nystagmus (beating in the same direction regardless of gaze, often suppressed when looking towards the fast phase) that is horizontal-torsional is typically associated with peripheral vestibular dysfunction. In contrast, direction-changing nystagmus (beating to the left when looking left, and to the right when looking right), purely vertical nystagmus, or purely torsional nystagmus, strongly suggests a central lesion.

The Test of Skew Deviation

The final component is the Skew test, which checks for vertical ocular misalignment. This is performed using a cover-uncover test. The patient is instructed to fixate on a target. One eye is covered for a few seconds, then uncovered, and the uncovered eye is observed for any vertical shift as it refixates. The procedure is then repeated on the other eye. The presence of Skew deviation—a vertical misalignment of the eyes that corrects when one eye is uncovered—is a significant indicator of a central vestibular lesion, often involving brainstem or cerebellar pathways. Unlike the other two components, Skew deviation is rarely seen in isolated peripheral vestibular disorders.

Interpreting the HINTS Battery

When all three tests are considered together, their combination provides powerful diagnostic information:

• HINTS suggestive of a peripheral lesion: An abnormal Head impulse test (corrective saccades), unidirectional nystagmus, and no Skew deviation.
• HINTS suggestive of a central lesion: A normal Head impulse test (no corrective saccades), or direction-changing/vertical/torsional nystagmus, or presence of Skew deviation.

The HINTS examination is a valuable tool in the acute setting, allowing for rapid and accurate differentiation between benign peripheral vertigo and potentially severe central pathology, guiding prompt and appropriate management decisions.