Some HINTS On Vertigo

Some HINTS on vertigo

Cerebellar infarction represents approximately 2.3 % of acute strokes overall.29 These can result from occlusion of the superior cerebellar artery (SCA), anterior inferior cerebellar artery (AICA), or the posterior inferior cerebellar artery (PICA). Larger cerebellar infarcts produce symptoms and signs localizing to the brainstem, such as diplopia, dysarthria, limb ataxia, dysphagia, and weakness or numbness. 

Approximately 10% of patients with cerebellar infarction can present with isolated vertigo, that is, vertigo with no localizing findings on motor, sensory, reflex, cranial nerve, or limb coordination examination. Most of these are infarcts of the medial branch of the PICA (96%).

Vertigo is defined as a pathologic illusion of movement. Most commonly experienced as a spinning sensation, it arises from a pathologic imbalance in the peripheral or central vestibular system.

Red flags in vertigo : 

1. Any neurologic deficit 
2. Total ipsilateral hearing loss
3. Inability to walk without support 
4. Direction-changing nystagmus

Rosen's provide this diagnostic algorithm.

Enter the HINTS examination

The HINTS examination is proposed as a method to elicit enough information to differentiate peripheral and central causes of constant vertigo (eg vestibular neuronitis vs cerebellar stroke) in a 3-test examination:

• Head Impulse testing
• Nystagmus
• Test of Skew

The HINTS study was published in 2009, describing 101 patients assessed by neurologists after referral for acute vestibular syndrome (vertigo, nystagmus, nausea/vomiting, head-motion intolerance, unsteady gait) in the presence of ≥1 stroke risk factor. These 3 examinations were found to have a sensitivity of 100% and specificity of 96% for a central lesion using diffusion-weighted imaging MRI at up to 48 hours as the gold standard. In fact, this combination of examination findings was more sensitive than MRI at presentation, which was falsely negative in 8 patients with an ischaemic stroke (and detected on MRI up to 3 days later).

Obviously, this study was set in a group of high-risk patients with a high incidence of central causes. The clinical examination was done by neurologists, and there was no blinding of results.

Is there other evidence?

One recent study compared HINTS to traditional evaluation for stroke risk with ABCD2, showing HINTS to be more sensitive for detecting a central cause than both ABCD2 score and early MRI: Newman-Toker et al, HINTS outperforms ABCD2 to screen for stroke in acute continuous vertigo and dizziness. Acad Emerg Med. 2013 Oct;20(10):986-96

This study drew some criticism for using the ABCD2 score, which was derived to predict stroke risk after TIA, and for patient selection (190 patients with acute, persistent vertigo with nystagmus plus nausea/vomiting, head motion intolerance, and new gait unsteadiness—findings that are sufficient to, and for all these patients, did, justify hospitalisation from the ED). The proportion with posterior fossa stroke (59.5%) or other central causes (5.8%) was very high, whereas the proportion of unselected dizziness patients with stroke or TIA is 3.2%.

Opinion

The question should not be how accurate is the HINTS exam, but rather is it accurate enough to change decision-making on the undifferentiated AVS patient? The HINTS exam has the potential to supplement us in two ways. 

First in the high risk patient who you intend to admit for further evaluation, the HINTS exam would be used to rule out a central cause to their symptoms and the patient could be safely discharged. 

The second, that HINTS could aid our decision making process is in the low risk patient to help identify a subtle presentation of central vertigo which would otherwise go unnoticed. In the Newman-Toker trials, the HINTS exam was performed on a cohort that exhibited either trunk ataxia or gait instability, both of which are ominous findings. These are the high risk patients which we hope the HINTS exam will help us to further risk stratify into those who require admission and those who can be safely discharged. In a group as high risk as these, a sensitivity of 96% is not acceptable to safely rule out a central cause of the patient’s vertigo. Not to mention we have no idea about its inter-rater reliability and how well these tests function in the novice’s hands. 

Conversely how the HINTS exam performs in a group of AVS patients who are far more benign in their presentation is unknown. When used in a lower risk cohort (similar to the typical population we see in the Emergency Department with AVS), it may in fact lead to more diagnostic testing without a significant increase to our diagnostic yield.

Clearly the HINTS exam is an interesting and useful tool to evaluate patients with AVS. Whether it will ever be refined enough to aid us in our critical reasoning for the undifferentiated ED patient is still unknown. Presently it has been tested on a highly selected population, by a single tester, without any examination of inter-rater reliability. Until we can examine the HINTS performance in the ED, as performed by ED physicians, on our patients, we do not know what, if any benefit it contributes to our clinical decision-making.