Introduction

Acute dizziness and vertigo are common presentations to the Emergency Department. The challenge is to determine if the cause is peripheral or central, because a posterior circulation stroke, can present with almost identical symptoms to a peripheral cause such as vestibular neuronitis.

There no single symptom, examination finding or early imaging result can reliably exclude a central cause in every patient.

Several findings show how difficult it is to distinguish central from peripheral causes:

• 10–25% of patients with AVS have a stroke.
• About 50% of patients with AVS do not have nystagmus.
• A normal general neurological examination does not exclude stroke.
• Early MRI can miss approximately 20% of strokes in patients with AVS.
• HINTS should not be applied indiscriminately. It is useful when performed by appropriately trained clinicians in the correct patient population.
• New unilateral hearing loss may be an important clue to an anterior inferior cerebellar artery (AICA) stroke.

The recent JAMA Insights review by Edlow and Gold (1) provides an update on the assessment of acute vestibular syndrome (AVS), emphasising the value of neurological examination, particularly eye movements and gait.

1. What is acute vestibular syndrome?

The traditional definition of AVS is an acute onset of continuous dizziness or vertigo accompanied by nausea, vomiting, spontaneous nystagmus, postural instability, gait unsteadiness and intolerance of head movement, persisting for at least 24 hours. However we know that approximately half of patients presenting with AVS do not have nystagmus. We also know that symptoms may only be present for several hours.

The syndrome is characterised by acute, persistent vestibular symptoms, rather than by the presence of any single examination finding.

2. Causes of acute vestibular syndrome

AVS can result from pathology affecting either the peripheral vestibular apparatus or the central nervous system.

Vestibular neuritis

Vestibular neuritis, also called acute unilateral vestibulopathy, is the most common peripheral cause and accounts for approximately 40% of AVS cases. It occurs due to dysfunction of the vestibular nerve and produces acute dizziness or vertigo, imbalance and head-motion intolerance.

Labyrinthitis

Labyrinthitis involves inflammation of the inner ear labyrinth, affecting both vestibular and auditory function. Unlike isolated vestibular neuritis, labyrinthitis can cause new hearing impairment. However, acute unilateral hearing loss accompanying AVS may also be a manifestation of AICA territory stroke.

Posterior circulation stroke

Stroke is the most common central cause of AVS and accounts for approximately 10–25% of cases. The clinical presentation can similar to vestibular neuritis, and the absence of focal neurological deficits does not exclude a cerebrovascular event.

Other diagnostic considerations

BPPV typically produces brief, triggered episodes of vertigo, although some patients experience residual dizziness between episodes.

Ménière disease can occasionally mimic AVS, while vestibular migraine, multiple sclerosis, medication effects and Wernicke encephalopathy may produce central vestibular symptoms.

3. The clinical examination: five essential components

Five bedside examination components that help distinguish peripheral from central causes(1). The presence of even one finding suggesting a central cause should prompt concern for stroke or another central pathology.

These are:

Peripheral versus central findings

To further illustrate the difficulty in making the diagnosis, some central lesions may produce findings traditionally associated with peripheral disease ie., horizontal unidirectional nystagmus is not exclusively peripheral, and some central lesions may produce an abnormal head impulse test.

The head impulse test has been validated for diagnostic use in AVS patients with nystagmus, not those without it.

4. Nystagmus: absence does not exclude stroke

Nystagmus is one of the most useful components of the vestibular examination, but its interpretation requires care. Spontaneous nystagmus is present in only approximately half of patients with stroke-related AVS. The absence of nystagmus should raise concern for a central cause in a patient with persistent vestibular symptoms.

Peripheral pattern

Vestibular neuritis typically produces spontaneous horizontal, unidirectional nystagmus ie., the fast phase beats in the same direction regardless of whether the patient looks left or right.

Central lesions can also produce unidirectional horizontal nystagmus.

Central patterns

The following findings suggest a central cause:

5. Skew deviation

Skew deviation reflects vertical misalignment of the eyes and may indicate central vestibular pathology. It is assessed using the alternate cover test.

The patient to look at a fixed target. One eye is covered and and then the other, observing the uncovered eye for a vertical corrective movement. A vertical refixation movement, either upwards or downwards, suggests skew deviation and a potential central cause. However a negative test does not independently exclude stroke.

6. The head impulse test

The head impulse test assesses the vestibulo-ocular reflex (VOR), a reflex that allows the eyes to fix on a target during rapid head movement.

To perform the test ask the patient to maintain fixation on the examiner’s nose. Turn the patient’s head briskly approximately 15 degrees to either side, repeating the movement several times. In a normal response, the eyes remain fixed on the target. If the vestibulo-ocular reflex is impaired, the eyes move with the head and then rapidly return to the target through a corrective saccade.

A corrective saccade suggests peripheral vestibular dysfunction, particularly vestibular neuritis. However, certain central lesions, including lesions involving the vestibular nucleus, may also produce an abnormal response.

Normal head impulse test has a sensitivity of 80% for central AVS (95% CI 72–88%).

7. The neurological examination: important but insufficient

Traditional neurological examination findings suggesting a central cause include:

However, these findings are frequently absent in patients with posterior circulation stroke.

The diagnostic performance for an abnormal neurological examination is a sensitivity of  46.8% and specificity of 92.8% More than half of central cases may lack abnormalities detected by the general neurological examination.

Eye movement assessment and gait examination are essential additions to the traditional neurological examination.

8. New hearing loss: an important stroke warning sign

Traditionally, hearing loss accompanying vertigo may lead clinicians towards a diagnosis of labyrinthitis. However, hearing loss can also occur with AICA territory infarction. The AICA supplies structures involved in vestibular and auditory function, making combined acute vestibular and hearing symptoms particularly important.

9. Gait assessment

Gait examination is especially important when spontaneous nystagmus is absent.

Patients with vestibular neuritis may have significant imbalance but are generally able to stand and walk independently or with minimal assistance. By contrast, severe truncal instability and inability to walk independently strongly suggest central pathology. In that study, none of the patients with AICA stroke could walk without holding onto a wall or another person.

Assess whether the patient can:

Severe inability to sit or stand independently, or inability to walk without substantial assistance, is a central warning sign. However, normal or near-normal gait does not completely exclude stroke.

10. HINTS

HINTS combines three components:

H – Head Impulse
N – Nystagmus
TS – Test of Skew

It was developed to differentiate peripheral from central causes of AVS in appropriately selected patients.

Findings suggesting a central cause

The original research demonstrated exceptional diagnostic performance when the examination was performed by highly experienced neuro-otologists. However, subsequent evidence demonstrates lower performance across broader clinical settings.

A meta-analysis of 14 observational studies involving 1,781 patients reported a HINTS sensitivity of 93% and a specificity of 83%. HINTS requires proficiency in recognising subtle eye movement abnormalities and understanding the appropriate patient population.  Incorrect application or interpretation may produce false reassurance.

HINTS should not be applied to patients with brief positional episodes of vertigo or to AVS patients without nystagmus. Its diagnostic accuracy is established in patients with ongoing AVS and nystagmus, assessed by appropriately trained clinicians.

11. Imaging: why a normal CT is not enough

CT brain

Routine CT imaging for every patient with AVS is not recommended by the GRACE-3 guidelines, due to its poor sensitivity of 20%  for detecting ischaemic stroke in this setting. A normal CT brain therefore provides little reassurance when the clinical concern is posterior circulation ischaemia.

MRI brain

MRI is the preferred imaging modality when the examination or clinical assessment suggests a central cause. MRI performed within 48 hours of symptom onset has a sensitivity of approximately 80% for stroke in AVS patients. A negative early MRI should not automatically override concerning bedside findings.

When should vascular imaging be considered?

The authors specifically recommend CT angiography or MR angiography in patients with AVS accompanied by severe headache or neck pain, to evaluate for vertebral artery dissection.

This is particularly relevant when symptoms suggest a vascular mechanism.

12. A practical emergency department approach

Take-home messages

References

Other reviews that may be of interest:

Diagnosing the dizzy patient. (recording of the HINTS examination)

Diagnosing a patient with vertigo in 5 steps

A Clinical Risk Score to identify serious causes of vertigo