HINTS

HINTS is an acronym for Head Impulse, Nystgmus, Test of Skew, a three-step bedside examination helpful in distinguishing acute peripheral vestibulopathy from structural disease of the posterior fossa, especially brainstem stroke.(1,2) The head impulse test is a bedside evaluation of the integrity of the vestibulo-ocular reflex (VOR). The examiner briskly rotates the patient’s head while having the patient fixate on a target, usually the examiner’s nose. When impaired, the VOR cannot match the velocity of head rotation, causing the eyes to lag behind and requiring a corrective saccade back to the target. An abnormal HIT indicates peripheral vestibular hypofunction on the side towards which the head was rotated.

One of the characteristics of vestibular nystagmus is consistency of direction. It may vary in intensity, but the fast phase always beats away from the impaired labyrinth. In contrast, nystagmus of central origin often changes direction. Skew deviation is a comitant vertical ocular malalignment, typically due to a stroke involving the prenuclear brainstem vertical ocular control mechanisms. The deviation remains the same in all directions of gaze. With other causes of vertical malalignment, such as IVth nerve palsy, the deviation changes in various directions of gaze (noncomitant). Skew deviation does not occur with peripheral vestibular lesions.

On HINTS testing, the patient with acute peripheral vestibulopathy, as in acute viral labyrinthitis, has an abnormal HIT, showing a corrective saccade, unidirectional nystagmus and no skew deviation. The patient with acute vertigo due to a brainstem stroke or other structural CNS pathology has a normal HIT, with no corrective saccade, direction changing nystagmus and may have skew deviation. A central finding on any of the three tests suggests a central lesion. The pattern of findings on HINTS testing can thus help distinguish an acute peripheral vestibular disturbance from acute structural pathology of the posterior fossa.

MRI is sometimes normal in acute brainstem stroke. In a study of 190 patients with acute vertigo, HINTS substantially outperformed ABCD2 for stroke diagnosis in the ED and also outperformed MRI obtained within the first 2 days after symptom onset. For any central lesion, sensitivity was 96.8%, specificity was 98.5%, LR+ was 63.9, and LR- was 0.03. Initial MRIs were falsely negative in 14.3% of acute infarctions. (3) HINTS can identify acute strokes more accurately than even MRI-DWI. (4). In a study of 91 patients with acute vertigo, HINTS had a sensitivity of 88% and a specificity of 96%. (5) In another study of 114 patients, HINTS had a sensitivity of 100% and a specificity of 94.4%. (6)

Gold and Tourkevich created a demonstration and discussion of the HINTS for the Neuro-Ophthalmology Virtual Education Library at the University of Utah.

References

1. Kattah JC, Talkad AV, Wang DZ, et al. HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke. 2009;40:3504-10.

2. Newman-Toker DE, Curthoys IS, Halmagyi GM. Diagnosing Stroke in Acute Vertigo: The HINTS Family of Eye Movement Tests and the Future of the "Eye ECG". Semin Neurol. 2015;35:506-21.

3. Newman-Toker DE, Kerber KA, Hsieh YH, et al. HINTS outperforms ABCD2 to screen for stroke in acute continuous vertigo and dizziness. Acad Emerg Med. 2013;20:986-96.

4. Saber Tehrani AS, Kattah JC, Mantokoudis G, et al. Small strokes causing severe vertigo: frequency of false-negative MRIs and nonlacunar mechanisms. Neurology. 2014;83:169-73.

5. Batuecas-Caletrío Á, Yáñez-González R, Sánchez-Blanco C, et al. Peripheral vertigo versus central vertigo. Application of the HINTS protocol. Rev Neurol. 201416;59:349-53.

6. Carmona S, Martínez C, Zalazar G, et al. The Diagnostic Accuracy of Truncal Ataxia and HINTS as Cardinal Signs for Acute Vestibular Syndrome. Front Neurol. 2016;7:125.