Boring Question: Dizzy, need a few HINTS?

The dizzy patient. If you haven’t seen a patient with this chief complaint, you either don’t work in an emergency department or you work in an imaginary emergency medicine utopia! Admit it, when you pick up the chart that reads “chief complaint…dizzy”, you look around inconspicuously, slowly replace that chart in the rack… and run quickly become preoccupied with some fascinating task from… oh… somewhere over there! But why? It is not because we do not like dizzy patients… It is because when the patient complains of ‘dizziness,’ it can mean so many things that it makes it hard for us to diagnose and solve the problem.

“Dizzy” is a vague problem that can be caused by a long list of diagnoses including critical or life-threatening diagnoses (e.g. posterior circulation infarction) that mimic benign causes of dizziness. Wouldn’t it be great if there was a blood test to rule-out serious pathology among dizzy patients? Unfortunately, we’re more likely to put humans on Mars than come up with such a test, so instead we are left to work up dizzy patients using our clinical skills and some focused diagnostic tests.

This post will present the case of a dizzy patient and outline how the HINTS examination can be integrated into our evaluation.

CASE

A 72 year old woman presents after acute onset “dizziness” that has been continuous for 36 hours. She describes feeling nauseated (without vomiting) and unsteady while ambulating. She has a history of hypertension but no other relevant medical history. Her vital signs are normal and exam demonstrates slight difficulty walking and horizontal nystagmus on right lateral gaze. The remainder of neurologic exam is normal. You wonder if this could be a posterior circulation infarct or is it simply a benign case of vertigo? You can’t get an MRI easily for several days so the decision needs to be made now. While you are considering your super keen medical students asks if the HINTS exam can play a role in sorting out the diagnosis for this patient.

Boring Question: What is the role of the HINTS examination in the evaluation of the dizzy patient?

The Head Impulse Nystagmus Test of Skew (HINTS) exam is a promising bedside test designed to differentiate between peripheral and central causes of acute vestibular syndrome (AVS). AVS is characterized by acute onset vertigo with associated nausea/vomiting, nystagmus, unsteady gait and head motion that persist >24hrs [1]. In most instances, HINTS is used to differentiate between vestibular neuritis and a posterior circulation infarct. However it may also identify other important central causes of AVS including mass lesions or demyelinating syndromes [2].

The HINTS Test comprises 3 parts [2]

Head impulse test (HIT) – the examiner performs rapid, passive head rotation of the patient while the patient fixates on the nose of the examiner; a peripheral etiology will cause a corrective saccade that is considered “abnormal” while a central cause of vertigo will lack any saccade thus considered “normal”. Bottom line is that “abnormal” is a good thing for the HIT and “normal” suggests a central etiology

Nystagmus type – identification of nystagmus type by smooth pursuit of extra ocular movements:
1. Central etiology = bilateral, direction-changing, horizontal nystagmus or primarily vertical nystagmus
2. Peripheral etiology = nystagmus is unilateral, horizontal nystagmus

Test of skew (alternate cover test) – in central causes of vertigo, covering of one eye results in subtle movement of the uncovered eye

This may be a bit overwhelming so I recommend watching this great video describing the HINTS exam [3,4]

HOW TO INTERPRET THE RESULTS OF HINTS?

HINTS exam in peripheral vertigo

Unilateral “abnormal” head impulse test PLUS unilateral horizontal nystagmus without any skew deviation.

HINTS exam in central vertigo

Any of, or combination of the following:

1) bilateral “normal” HIT with any spontaneous or gaze-evoked nystagmus

2) bilateral, direction-changing, horizontal gaze-evoked nystagmus

3) skew deviation

Try using the mnemonic INFARCT to recall the findings in central vertigo. INFARCT = (Impulse Normal or Fast-phase Alternating or Refixation on Cover-Test) [7]

HOW ACCURATE IS HINTS?*

Very accurate – several studies report HINTS to be highly sensitive (96-100%) and highly specific (85-98%) for identifying stroke among patients with AVS [2, 5]
Impressively, HINTS exam was also more accurate than MRI to diagnose stroke in patients with AVS within the first 48hrs of symptoms [2]
Most studies used HINTS to differentiate posterior stroke from peripheral causes of AVS but it can be broadly to differentiate between any central vs peripheral pathology [6]
A recent review highlights the impressive accuracy of HINTS in vertigo [6]

CONSIDERATIONS FOR HINTS EXAM

It should ONLY be used for persistent and continuous vertigo. A patient without vertigo during the exam will have a “normal” head impulse test which is the same finding that will occur in a patient with central vertigo

The few studies that exist have enrolled patients with vertigo >1hr since most patients present soon after the onset. So while AVS is technically defined as >24hrs, you can use the HINTS exam if it’s <24hrs as long as the symptoms are continuous

Most of the studies required that patients had at least one risk factor for stroke. As a result the populations studied may have a higher risk of a central etiology. At this time it is unclear the accuracy of HINTS among lower risk populations (e.g. 40 year old male without any other risk factors)

In one study patients were included if they had “vertigo” or “dizziness” plus the other components of AVS . So don’t necessarily exclude your patient because they don’t use the term “vertigo” [2]. However, do your best to establish that they’re experiencing the sensation of movement (either self- or external referenced)

Finally, the majority of studies evaluating the utility of HINTS had highly trained clinicians performing the neurologic evaluations [2,5,8]. The data has not been externally validated among a general population of emergency physicians. So proceed with caution! We shouldn’t expect the same high sensitivity and specificity when used by non-expert clinicians.

BACK TO THE CASE

Symptomatic relief using anti-nausea medications results in some symptomatic improvement of the patient but the symptoms do not entirely resolve. You perform the HINTS exam on the patient. She has a “normal” head impulse test without any saccade. She has unilateral, gaze-evoked nystagmus without any vertical or bidirectional nystagmus. And there is no skew deviation. Based on these findings you’re concerned there is a central cause for her vertigo. She is referred and admitted to the neurology team. An MRI the following day confirms a cerebellar infarct.

CONCLUSION

The HINTS exam has an important role in the evaluation of AVS based on existing data
It is highly accurate in identifying central causes of AVS, perhaps superior to MRI in early stages
These impressive results we however comes from one centre where highly trained experts performed the exam so if there is any uncertainty do not rely exclusively on HINTS for diagnosis

This post was edited by Teresa Chan (@TChanMD)

*16/5/15: A previous version of this post stated that the evidence for HINTS was ‘VERY STRONG’ but referred to its accuracy. This has been modified to be more clear that this statement was referring to HINTS’ accuracy. Thanks to the good folks at the SOCMOB blog for pointing out the potential confusion.

References

1. Hotson, J. R., & Baloh, R. W. (1998). Acute vestibular syndrome. New England Journal of Medicine, 339(10), 680-685. DOI: 10.1056/NEJM199809033391007

2. Newman‐Toker, D. E., Kerber, K. A., Hsieh, Y. H., Pula, J. H., Omron, R., Saber Tehrani, A. S., … & Kattah, J. C. (2013). HINTS outperforms ABCD2 to screen for stroke in acute continuous vertigo and dizziness. Academic Emergency Medicine, 20(10), 986-996. Link

3. EMCrit http://emcrit.org/misc/posterior-stroke-video/ and the original source of the videos is http://novel.utah.edu/Newman-Toker/collection.php

4. Newman-Toker D. 3-Component H.I.N.T.S. battery. (2009). Retrieved at: http://content.lib.utah.edu/cdm/singleitem/collection/ehsl-dent/id/6

5. Chen, L., Lee, W., Chambers, B. R., & Dewey, H. M. (2011). Diagnostic accuracy of acute vestibular syndrome at the bedside in a stroke unit. Journal of neurology, 258(5), 855-861. DOI: 10.1007/s00415-010-5853-4

6. Cohn, B. (2014). Can Bedside Oculomotor (HINTS) Testing Differentiate Central From Peripheral Causes of Vertigo?. Annals of emergency medicine. In Press. DOI: 10.1016/j.annemergmed.2014.01.010

7. Newman-Toker D. Acute Vestibulary Syndrome (n.d.) Retrieved at: http://content.lib.utah.edu/utils/getfile/collection/ehsl-dent/id/7/filename/5.pdf

8. Kattah, J. C., Talkad, A. V., Wang, D. Z., Hsieh, Y. H., & Newman-Toker, D. E. (2009). HINTS to diagnose stroke in the acute vestibular syndrome three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke, 40(11), 3504-3510. DOI: 10.1161/STROKEAHA.109.551234