Diagnosing Stroke in Acute Vertigo: The HINTS Family of Eye Movement Tests and the Future of the "Eye ECG"

Abstract

Patients who present to the emergency department with symptoms of acute vertigo or dizziness are frequently misdiagnosed. Missed opportunities to promptly treat dangerous strokes can result in poor clinical outcomes. Inappropriate testing and incorrect treatments for those with benign peripheral vestibular disorders leads to patient harm and unnecessary costs. Over the past decade, novel bedside approaches to diagnose patients with the acute vestibular syndrome have been developed and refined. A battery of three bedside tests of ocular motor physiology known as "HINTS" (head impulse, nystagmus, test of skew) has been shown to identify acute strokes more accurately than even magnetic resonance imaging with diffusion-weighted imaging (MRI-DWI) when applied in the early acute period by eye-movement specialists. Recent advances in lightweight, high-speed video-oculography (VOG) technology have made possible a future in which HINTS might be applied by nonspecialists in frontline care settings using portable VOG. Use of technology to measure eye movements (VOG-HINTS) to diagnose stroke in the acute vestibular syndrome is analogous to the use of electrocardiography (ECG) to diagnose myocardial infarction in acute chest pain. This "eye ECG" approach could transform care for patients with acute vertigo and dizziness around the world. In the United States alone, successful implementation would likely result in improved quality of emergency care for hundreds of thousands of peripheral vestibular patients and tens of thousands of stroke patients, as well as an estimated national health care savings of roughly $1 billion per year. In this article, the authors review the origins of the HINTS approach, empiric evidence and pathophysiologic principles supporting its use, and possible uses for the eye ECG in teleconsultation, teaching, and triage.

Figure 1.. Timeline showing major milestones in the development of HIT, HINTS, and VOG-HINTS testing

Figure 2.. Receiver operating characteristic curve analysis for the ‘HINTS family’ compared to neuroimaging (CT or MRI) and vascular risk stratification by ABCD² score for detecting stroke in patients presenting the acute vestibular syndrome.

Receiver operating characteristic (ROC) curves shown for three different diagnostic approaches to diagnosing stroke in the acute vestibular syndrome. The reference diagonal line indicates a hypothetical useless diagnostic test with a likelihood ratio of 1.0 at all threshold cutoffs. Such a test provides no additional information about the underlying diagnosis. A perfect test or decision rule has threshold cutoffs in the upper left corner (100% sensitivity, 100% specificity) and an area under the curve (AUC) of 1.0. The AUC for the HINTS family of tests is estimated to be 0.995 in this patient population. Note that the horizontal HIT alone outperforms MRI for diagnosing stroke in the first 24–48 hours after the onset of acute, continuous vertigo. Abbreviations: ABCD2 – age, blood pressure, clinical features, duration of symptoms, diabetes; CT – computed tomography; HINTS – head impulse, nystagmus, test of skew; HINTS “plus” – HINTS plus new hearing loss detected by finger rubbing; HIT – head impulse test; MRI – magnetic resonance imaging Adapted from Newman-Toker, et al., Academic Emergency Medicine, 2013

Figure 3.. Physiologic attributes and parameter definitions for a single, typical, abnormal h-HIT trace.

Head velocity traces are shown in red, eye velocity in black. Note that eye movements are in the opposite direction to head movements, but are displayed graphically as superimposed to make visual assessment of VOR gain (eye movements relative to head movements) clearer. H0 = Head velocity onset; E0 = eye velocity onset; H _peak = peak head velocity; E _peak = peak eye velocity; H _bounce = head velocity crosses baseline with head reversal following deceleration (bounce); H _stop = head movement stops; E _stop = eye movement stops; CCS = covert corrective saccade (during head movement); OCS = overt corrective saccade (after head movement) with dotted line (slope = saccade acceleration) to identify E1 saccade onset; VOR latency = E0 – H0; VOR gain = eye velocity divided by head velocity at a specific time during the HIT (generally E _peak /H _peak ) or across a range of times (E _times /H _times ) (generally the ratio of the areas under the two curves over the entire HIT duration); saccade latency = E1 – E0. Reproduced with permission from Mantokoudis, et al. Audiology & Neuro-otology, 2015

Figure 4.. Physiologic (VOG) diagnosis of neuritis vs. stroke in two acute vertigo patients in the ED.

Clinical features were the same for both patients (vertigo, nausea, and gait disturbance without neurologic or auditory symptoms or signs). Both had unidirectional nystagmus (first degree in light with visual fixation) without skew deviation. Shown are physiologic tracings from high-speed video recordings of multiple rightward (A;E) and leftward (B;F) h-HIT maneuvers temporally superimposed with a single maneuver bolded. The abnormal h-HIT (A) has both a quantitative abnormality (reduced VOR gain during the head movement, downward red arrow) and a qualitative, clinically-evident abnormality (fast, corrective eye movements to realign the eye on the target after the head stops moving, red chevrons). Each h-HIT result is mapped in the corresponding VOR gain plot (C;G) where the central ‘x’ denotes the mean right- or left-sided VOR gain across h-HIT trials. Representative axial MRI-DWI images through the inferior cerebellum show no stroke in the older vestibular neuritis patient (D) and a large acute, left posterior inferior cerebellar artery territory infarction in the younger stroke patient (H, arrow). The 60 year old is the typical patient who would most likely undergo an unnecessary $10,000 stroke workup and admission; the 30 year old, whose stroke spanned 8 axial slices (lesion 3.0×5.0×4.4 cm), is the typical patient who may be missed and sent home as a ‘peripheral’ and whose stroke may swell, causing hydrocephalus, herniation, and death. Abbreviations: h-HIT – horizontal head impulse test; MRI-DWI – magnetic resonance imaging with diffusion weighted imaging; VOR – vestibulo-ocular reflex; °/s – degrees per second; yo – year old Adapted from Newman-Toker et al., Stroke 2013