If you were to suddenly be hit with serious symptoms of vertigo, nausea or vomiting – you would likely make your way to the emergency room. If you live in the United States, you would be one among 2.6 million patients who visit the emergency room every year for the exact set of same symptoms.

You would almost definitely be sent off for an MRI and CT scan and very likely be diagnosed with acute vestibular syndrome (AVS). More specifically, your symptoms would likely be attributed to a virally-induced inflammation, known as an acute peripheral vestibulopathy (APV).You might even be told (incorrectly) that you are fine and be sent home.

However, while many patients presenting with AVS symptoms are clustered as APV, they are actually suffering from a different problem altogether – namely, posterior strokes.

Why do such a large number of patients receive a misdiagnosis? The reason is two-fold. First off, brain scans, such as MRI and CT, are unreliable diagnostic tools when used on their own (in fact, false negatives are quite common). Secondly, patients with these posterior strokes often mimic many of the same symptoms found in APV.

Specifically, patients with Acute Vestibular Syndrome (AVS) typically show the following set of symptoms:

• Rapid onset (over seconds to hours) of vertigo
• Nausea and/or vomiting
• Gait unsteadiness in association with head-motion intolerance
• Nystagmus lasting days to weeks.

In a key clinical study, high-risk patients with AVS were put through a battery of bedside oculomotor tests to determine whether these tests could more reliably identify the occurrence of a posterior stroke in patients with AVS. In the study, the researchers assessed the sensitivity of a 3-step oculomotor bedside test, known as the Head-Impulse-Nystagmus-Test-of-Skew (HINTS) for identifying posterior stroke in patients who may have otherwise received an AVP misdiagnosis.

The HI in HINTS: Horizontal Head Impulse test (h-HIT)

The horizontal head impulse test (or h-HIT) is used to assess proper vestibular ocular reflex (VOR) function and is the first step in the 3-step test “HiNTS” used to test for a potential posterior stroke.

The patient is asked to look straight ahead at a fixed point (often the doctor’s nose) and the head is then moved side to side. By displacing the head laterally by approximately 20 degrees and rotating rapidly back to the midline. If the patient is able to successfully remain fixated on the target (nose or otherwise), this is considered a normal response (i.e. intact VOR) and paradoxically is suggestive of a posterior stroke. An abnormal h-HIT is suggestive of a peripheral cause of vertigo.

The N in HiNTS: Nystagmus test

The second step in the 3-step “HINTS” is a test for nystagmus (involuntary, rapid and repetitive movement of the eyes). Most patients who present an AVS show a characteristic and dominantly horizontal nystagmus, which beats only in one direction and increases in intensity when the patient looks in the direction of the nystagmus fast phase. While nystagmus is not unique to patients with AVS, patients with a central AVS will sometimes exhibit a change in the direction of eccentric gaze, whereas those with AVP will not. Thus, this test is another reliable predictor of a central pathology.

The TS in HINTS: Test of Skew Deviation

The third and final step is a test for skew deviation, a vertical ocular misalignment which results from an imbalance in neural firing (predominantly from the otolithic inputs into the oculomotor system). When functioning properly, the otolithic inputs sense motion and tilt of the head and transmit this information into the midbrain. In pathology, skew deviation is suggested to be a specific sign of a central issue in patients presenting with AVS.

The predictive power of HINTS

Previous literature has suggested that the three subtle oculomotor signs described above might, collectively, be the best predictor of stroke in AVS. In the Kattah et al, study results of the HINTS exam were defined (a priori) as either benign or dangerous, as follows:

A benign HINTS exam presents with

• Abnormal h-HIT
• Direction-fixed horizontal nystagmus
• Absent skew

A dangerous HINTS exam presents with

• Normal/untestable h-HIT
• Direction-changing horizontal nystagmus
• Present/untestable skew deviation

The researchers then tested whether a dangerous HINTS exam successfully predicted the presence of a stroke or whether a benign HINTS exam successfully ruled out the presence of a stroke. The results of their analysis demonstrated that the HINTS exam does indeed provide an increased sensitivity and specificity of stroke detection, relative to other methods.

As a bedside test, which takes approximately one minute to conduct, the 3-step HINTS exam not only improves diagnostic accuracy, but also represents a significant advantage in time and cost spent compared to traditional neurological examination methods.

References

Kattah JC, Talkad AV, Wang DZ, Hsieh YH, & Newman-Toker DE (2009). HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke; a journal of cerebral circulation, 40 (11), 3504-10 PMID: 19762709

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