Take a HINTS

A 65-year-old gentleman with hypertension and hyperlipidemia presents to your emergency department one evening complaining of continuous vertigo that began suddenly two hours prior to arrival. He notes significant head motion intolerance, is nauseated, and has vomited several times. On exam, he has horizontal nystagmus in lateral gaze, is very unsteady on his feet, but otherwise has a normal neurologic exam.

A 65-year-old gentleman with hypertension and hyperlipidemia presents to your emergency department one evening complaining of continuous vertigo that began suddenly two hours prior to arrival. He notes significant head motion intolerance, is nauseated, and has vomited several times. On exam, he has horizontal nystagmus in lateral gaze, is very unsteady on his feet, but otherwise has a normal neurologic exam. He denies hearing changes, recent URI symptoms and lightheadedness. His head CT, ECG, and labs are normal, and after receiving 25 mg of oral meclizine, he notes moderate improvement in his symptoms. He is now able to ambulate without assistance, with minimal ataxia, and is asking if he can go home. You ask yourself how confident you are that this gentleman’s vertigo is peripheral in nature, and you entertain the possibility that he has suffered a cerebellar stroke. You then consider the options: 1) discharge the patient home with oral meclizine to take as needed; 2) admit the patient to the hospital for a brain MRI and a neurology consult; or 3) call the neurologist at home to ask for assistance. What you really want is a cheap, quick bedside test to help differentiate central from peripheral vertigo.

Dizziness remains one of the more challenging chief complaints encountered in the emergency department. This complaint encompasses a wide variety of symptoms, including vertigo, lightheadedness, weakness, and just plain not feeling good. Even when the symptom truly is vertigo, the diagnostic conundrum is no less daunting, as the symptom type is not a good predictor of cause. The challenge becomes differentiating benign peripheral vertigo from potentially life-threatening central vertigo, often the result of a cerebellar stroke. While a normal neurologic exam may feel reassuring to most clinicians, focal neurologic deficits are unfortunately frequently absent in cases of posterior circulation stroke. CT scan is often the initial imaging modality when stroke is being considered, but is notoriously insensitive, particularly when it comes to the posterior fossa, missing 60-90% of acute ischemic strokes in the brainstem or cerebellum. MRI with diffusion-weighted imaging, considered by many to be the “gold standard” for the diagnosis of stroke, is more reliable than CT, but is still far from perfect. Around 15-20% of patients with posterior circulation stroke will have a normal MRI in the early period. In addition, MRI is expensive, costly, and not available in most emergency departments. When posterior circulation stroke is considered in patients with vertigo, hospital admission or transfer is often required to complete the necessary work-up.

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A rapid, bedside test to help differentiate central from peripheral vertigo would therefore have great value. The HINTS exam has been proposed as just such a test. HINTS stands for Head Impulse, Nystagmus, and Test of Skew, and is a three-part oculomotor test. If any portion of the test indicates a central etiology, the test is considered positive and further evaluation for stroke (or other central pathology) is warranted. The three components of the exam are as follows:

1 – Patients with peripheral vertigo will have abnormal (positive) head impulse testing, while patients with central vertigo typically have a normal (negative) head impulse test.

Horizontal head impulse testing involves rapid head rotation by the examiner with the subject’s vision fixed on a nearby object (often the examiner’s nose). With rapid low-amplitude rotation of the head toward the midline, the patient’s eyes should remain fixed on the target. In cases of peripheral vertigo, in which the vestibulo-ocular reflex is impaired, rapid rotation of the head toward the affected side will result in loss of fixation and movement of the eyes away from the target. This is followed by a corrective saccade as the subject looks back toward the target. Observation of this corrective saccade is abnormal, and considered a positive test. There is typically no corrective saccade in patients with central vertigo, in whom the vestibulo-ocular reflex usually remains intact. In rare cases of combined stroke and inner ear infarction, patients may have an abnormal head impulse test. In such cases, the central nature of the lesion will be revealed instead by one of three other findings: direction-changing nystagmus, skew deviation, or unilateral hearing loss.

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2 – Patients with peripheral vertigo will have unidirectional, horizontal nystagmus, while patients with central vertigo can have rotatory or vertical nystagmus, or direction-changing horizontal nystagmus. 

In peripheral vertigo, it is common to have a horizontal-beating nystagmus with a fast phase that is unidirectional, beats away from the affected side, and increases in intensity when the patient looks in the direction of the fast phase. While vertical or rotational nystagmus reliably indicates an underlying central pathology, patients with central vertigo more typically have horizontal-beating nystagmus, mimicking peripheral vertigo. In such cases, the direction of the fast phase may change on eccentric gaze, i.e., the fast phase beats in one direction when looking to the right, and the opposite direction when looking to the left (or on returning to the midline). This direction-changing nystagmus reliably excludes a peripheral etiology.

3 – Alternate eye cover testing may reveal skew deviation in patients with central vertigo, and should be absent in peripheral vertigo.

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Patients with central pathology as a cause of vertigo will frequently have a right-left imbalance in otolith (gravity-sensing) function, resulting in a vertical misalignment of the eyes (i.e. one eye’s gaze slightly higher than the other). While focused on a fixed target, each eye is alternately covered. As the cover is moved from one eye to the other, the now uncovered eye must correct for the misalignment and will look up (or down) to focus back on the target. As the cover is moved back to the other eye, the newly uncovered eye will have to look down (or up) to correct its gaze back to the target. This slight correction is observed repeatedly as the cover is moved back and forth, from one eye to the other. Such ocular misalignment and skew deviation (with or without an associated head tilt and ocular fundus torsion) is frequently seen in patients with posterior fossa abnormalities (i.e. brainstem strokes). Alternate cover testing in patients with peripheral vertigo should result in no skew deviation or ocular tilt in the vast majority of cases.

Several points need to be considered when using the HINTS exam.  Most importantly, the exam should be performed only on patients with continuous vertigo.  In patients without active, continuous vertigo, the vestibulo-ocular reflex will remain intact and head impulse testing will be normal, with no corrective saccade observed.  This will be true in both patients with BPPV and in those without vertigo at all.  Such a finding is misleading, as it is considered indicative of a central pathology. This can lead to further unnecessary testing or hospital admission in such patients.

Before implementing the HINTS exam in one’s practice, the practitioner must exercise extreme caution. The HINTS exam has demonstrated excellent accuracy in distinguishing central from peripheral vertigo, but studies thus far have evaluated its use in the hands of neuro-ophthalmologists and neuro-otologists, whose familiarity with each component of the exam is likely to be much higher than the average emergency physician’s. In one study, neurologists tasked with performing the HINTS exam underwent a 4-hour tutorial prior to testing. Studies thus far have not evaluated the HINTS exam in the hands of the emergency physician, and additional training may be necessary before its routine use can be recommended.

Some may argue that the HINTS exam has limited utility in emergency department patients. Many feel that patients in whom stroke is considered should undergo MRI, or be admitted for further evaluation by a neurologist. However, the HINTS exam has been proven reliable when performed appropriately, and when negative should obviate the need for further testing in all but the highest-risk patients. Given the lack of objective findings in most patients with central vertigo, the HINTS exam will be a means of detecting central pathology in many patients who would otherwise be discharged home. Additionally, given the lack of sensitivity of MRI early in the course of posterior stroke, patients with a negative MRI but positive HINTS exam should still be admitted for further observation and testing. The key to the HINTS success will lie in appropriate training. Most emergency physicians are either entirely unaware of the HINTS exam, or are at least unfamiliar with its performance and interpretation. In such cases, a low threshold for imaging and neurologic consultation should remain in place. In an effort to improve patient care, emergency physicians should look to become adept at performing and interpreting the HINTS exam, and this tool should become a part of emergency medicine residency training.

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Dr. Cohn practices emergency medicine at Washington University in St. Louis and is the director of the Washington University EM Journal Club

References

• Newman-Toker DE, Kerber KA, Hsieh YH, Pula JH, Omron R, Saber Tehrani AS, Mantokoudis G, Hanley DF, Zee DS, Kattah JC. HINTS Outperforms ABCD2 to Screen for Stroke in Acute Continuous Vertigo and Dizziness. Acad Emerg Med. 2013 Oct;20(10):986-996.
• Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE. HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke. 2009 Nov;40(11):3504-10.
• Newman-Toker DE, Kattah JC, Alvernia JE, Wang DZ. Normal head impulse test differentiates acute cerebellar strokes from vestibular neuritis. Neurology. 2008 Jun 10;70(24 Pt 2):2378-85.
• Oppenheim C, Stanescu R, Dormont D, Crozier S, Marro B, Samson Y, Rancurel G, Marsault C. False-negative diffusion-weighted MR findings in acute ischemic stroke. AJNR Am J Neuroradiol. 2000 Sep;21(8):1434-40.

Central vertigo video links

• www.youtube.com/watch?v=QaV2KuG6cnw (normal head impulse test)
• www.youtube.com/watch?v=B0ihEfYXPs0 (direction-changing nystagmus)
• www.youtube.com/watch?v=zgqCXef-qPs (positive test of skew)

Peripheral vertigo video links

• www.youtube.com/watch?v=Wh2ojfgbC3I (head impulse)
• http://www.youtube.com/watch?v=YntJiBCz3pA (unidirectional nystagmus)
• www.youtube.com/watch?v=eNpoGOANULI (negative test of skew)

Social Media

• Podcast http://emjclub.com/
• Twitter @emjclub
• Facebook https://www.facebook.com/emjclub
• Journal Club http://emed.wustl.edu/education/emergencymedicinejournalclub 

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For an easier Head Impulse Test, try using a slow motion app on your iPhone

by Scott Weingart, MD

The patient is asked to fixate on the lens of the iPhone as a partner moves the head laterally; the eye movements are filmed with the slowmo app.

The HiNts exam is a series of tests to evaluate patients with vestibular syndrome to see if the cause is a possible posterior stroke. One aspect of the exam, the Head Impulse test requires movement of the head in sudden, lateral, jerking motions while observing the eyes for catch-up saccades. Coordinating head movement with eye observation can be difficult for practitioners who are not neuro-ophthalmologists or stroke neurologists. By recruiting a helper to do the head motions, you only need to watch the eyes. Even easier is to film the eye motions and then watch the ocular motions in slow motion. Luckily, there’s an app for that: “slowmo”. This $0.99 app allows easy filming and playback of the Head Impulse test. Another app, “slowpro” is available for free, though I have not tried this one clinically.

No conflicts of interest with the app or iphones