What is a HINTS (Head Impulse Test, Nystagmus, and Test of Skew) exam?

HINTS Examination for Vertigo Diagnosis

The HINTS examination is a highly sensitive and specific bedside test that distinguishes between peripheral and central causes of vertigo, with its primary value being the early detection of potentially life-threatening stroke in patients with acute vestibular syndrome (AVS). 1

What is the HINTS Exam?

HINTS is an acronym that stands for:

• Head Impulse test
• Nystagmus observation
• Test of Skew deviation

This three-part bedside examination is specifically designed to differentiate between peripheral causes of vertigo (such as vestibular neuritis) and central causes (particularly stroke) in patients presenting with acute vestibular syndrome.

Components of the HINTS Exam

1. Head Impulse Test (HIT):

   • Examiner rapidly turns the patient's head horizontally while the patient fixates on a target
   • A normal response (negative test) shows the eyes remaining fixed on target
   • An abnormal response (positive test) shows corrective saccades after head movement
   • Abnormal HIT suggests peripheral pathology; normal HIT in AVS suggests central pathology

2. Nystagmus Observation:

   • Examiner observes the direction and characteristics of nystagmus in different gaze positions
   • Direction-changing nystagmus in eccentric gaze suggests central pathology
   • Unidirectional horizontal nystagmus suggests peripheral pathology

3. Test of Skew:

   • Examiner checks for vertical misalignment of the eyes using alternate cover test
   • Presence of skew deviation (vertical ocular misalignment) suggests central pathology
   • Skew deviation is particularly associated with brainstem lesions 2

HINTS Plus

Some clinicians use an expanded version called "HINTS Plus" which adds:

• Assessment of hearing loss (sudden unilateral hearing loss may indicate involvement of the anterior inferior cerebellar artery) 3

Diagnostic Accuracy

The HINTS examination demonstrates remarkable diagnostic power when properly performed:

• Sensitivity of 96.7% and specificity of 94.8% when performed by neurologists 1
• Higher sensitivity for stroke detection than early MRI (100% versus 46%) 1
• A meta-analysis showed that for peripheral HINTS pattern, the positive likelihood ratio was 17.3 and negative likelihood ratio was 0.15 4
• For central HINTS pattern (stroke), the positive likelihood ratio was 5.61 and negative likelihood ratio was 0.06 4

Clinical Application

HINTS is particularly valuable because:

• Up to 75-80% of patients with AVS related to stroke have no associated focal neurologic deficits 1
• The prevalence of cerebrovascular disease in AVS patients is approximately 25% and up to 75% in high vascular risk cohorts 1
• A properly performed HINTS exam showing a peripheral pattern may eliminate the need for neuroimaging in appropriate patients 1

Important Caveats and Pitfalls

1. Proper Training Required:

   • Diagnostic accuracy varies depending on examiner expertise 1
   • Most validation studies were performed by neurologists or specialists with neuro-otology or neuro-ophthalmology experience 4
   • Emergency physicians may have limited diagnostic value without proper training 5

2. Appropriate Patient Selection:

   • HINTS is specifically designed for patients with acute vestibular syndrome (continuous vertigo lasting >24 hours with nausea/vomiting and gait unsteadiness) 3
   • Not appropriate for patients with intermittent vertigo or without nystagmus 5
   • Should not be used simultaneously with Dix-Hallpike (which is for positional vertigo) 5

3. Timing Considerations:

   • Most effective when performed within 72 hours of symptom onset 2
   • Early MRI (within 48 hours) can be falsely negative in 12% of stroke cases 2

4. Interpretation Challenges:

   • Skew deviation can help identify stroke when an abnormal head impulse test falsely suggests peripheral lesion 2
   • The presence of all three signs (normal head impulse, direction-changing nystagmus, and skew deviation) is highly indicative of stroke 2

The HINTS examination represents a significant advance in bedside diagnosis of vertigo, allowing clinicians to rapidly differentiate between benign peripheral causes and potentially life-threatening central causes, particularly when imaging may be delayed or initially negative.