Tuesday, March 08, 2016

Review: HINTS to Diagnose Stroke in the Acute Vestibular Syndrome

AVS is characterized by rapid onset of vertigo, nausea/vomiting, and gait unsteadiness with head motion intolerance and nystagmus.  The most common cause tends to be viral in nature, affecting the inner ear.  While this may be the domain of our esteemed neurology colleagues, there are 2.6 million ED visits for dizziness or vertigo annually in the United States, where the differential between a benign viral cause of vertigo or dizziness must be delineated from potentially lethal causes such as brainstem or cerebellar strokes.

Vertigo and dizziness, especially in cases of labyrinthitis, is caused by inflammation along the semicircular canals, affecting the flow of fluid throughout the system and causing the brain to interpret tilt or head spinning when there is none.  However, these same systems can be disrupted by central nervous pathologies that affect the vestibulocochlear nerve or the pons, which CN VIII enters.  Acute stroke in the vertebrobasilar circulation along the brain stem can present with damage to CN VIII, the brain stem itself, or the cerebellar and surrounding structures that maintain balance.  This paper attempts to delineate a series of clinical tests that can be easily performed at bedside to help aide in diagnosis of vertebral stroke.

This paper focused on 101 patients with AVS who presented with new onset vertigo or dizziness, with the majority (59) coming from the emergency department directly and many others (37) being referred from affiliate hospital emergency departments.  Of these patients that were deemed “high risk” for stroke (70% with >2 risk factors for stroke, the other 30% with 1 risk factor), 25 had acute peripheral vestibulopathy while the remaining 76 had a central lesion diagnosed on MRI (of which there were 69 iscehmic strokes, 4 hemorrhages, 2 demyelinating, and 1 anticonvulsant toxicity).  Of the patients with a central lesion, 100% had at least one of three clinical signs: a normal h-HIT, or head impulse test, horizontal nystagmus with a change in direction in eccentric gaze, or skew deviation of the eyes.  These can be remembered via the acronym INFARCT (Impulse Normal, Fast-phase Alternating, Refixation on Cover Test).  Of these, the study found that a “normal” or benign HiNTS (Head impulse – Nystagmus – Test-of-Skew) was sufficient to rule out all given central causes of vertigo.  As such, they suggest the use of HiNTS exam as a screening tool to effectively rule out central causes of vertigo in affected patients.

The benign HiNTS exam relies on three clear exam maneuvers to determine the cause of the vertigo and dizziness.  The first maneuver, the “head impulse” test, is performed by standing in front of the patient, holding their head firmly, and using a rapid movement to the left or right while the patient is told to maintain focus on your nose.  A normal head impulse results in the patient maintaining strict focus on your nose due to the adjustment of the vestibular system to maintain smooth movement of the eye.  However, in peripheral causes of vertigo, this will be altered such that the eye will fail to fix on the patient and make a corrective saccade to refixate on your nose.  In that case, it is an abnormal head impulse test, but this also rules out a central cause of vertigo in that case.  The second test for the HiNTS exam is a simple test for extraocular motion, looking for a beating nystagmus in the vertical or horizontal directions.  The third maneuver is to check for skew deviation, which can help attend for function of the brain stem.  This is done via a simple cover-uncover test to see if there is any movement of the eyes.  However, this should be performed with care as the patient may have a baseline deviation due to previous strabismus or other condition leading to deviation of the eyesight.  The test for skew deviation is very specific for a brain stem lesion in the patient.  With these three signs together, you can call a HiNTS exam benign if there is a 1, abnormal head impulse test, 2, no nystagmus on extraocular motion exam, and 3, no deviation of the eyes on cover-uncover testing.

However, it becomes important to understand the limitations of the study.  The initial tests were performed with experienced neuro-ophthalmologists performing the exam in an outpatient setting as opposed to by EM physicians in the ED setting.  Also, it is important to note that in order to be considered “high-risk” for a stroke and have this study apply to you, you would need at least one stroke risk factor of smoking, hypertension, diabetes, hyperlipidemia, atrial fibrillation, eclampsia, hypercoagulable state, recent cervical trauma, prior stroke or myocardial infarction and not have any history of recurrent vertigo or auditory symptoms.  However, with increased training and awareness, this could become a vital skill for EM physicians in the diagnosis of stroke.

This study provides the basis for a vital tool for evaluating vertigo and dizziness in the ED and preventing the catastrophic results of misdiagnosing a lethal or debilitating disease as something benign.  The results of the study are impressive: a positive HiNTS was reported as having an initial sensitivity of 100% and a specificity of 96%.  Though we should be aware of the difficulties of this study, the HiNTS exam provides a valuable tool to help screen patients in the ED and is a useful skill to put in the toolbox of any practicing EM physicians.

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