What is the HINTS (Head Impulse Test, Nystagmus examination, and Test of Skew) exam for evaluating dizziness?

What is the HINTS Exam for Dizziness?

The HINTS exam is a three-component bedside eye movement battery (Head Impulse test, Nystagmus assessment, and Test of Skew) designed to differentiate between dangerous central causes (particularly stroke) and benign peripheral causes of acute vestibular syndrome, and when performed by properly trained clinicians, it is more sensitive than early MRI for detecting posterior circulation stroke. 1, 2

Components of the HINTS Exam

The exam consists of three distinct eye movement tests that must be performed in patients with acute vestibular syndrome:

Head Impulse Test

• Assesses the vestibulo-ocular reflex by rapidly rotating the patient's head while they fixate on a target 1
• An abnormal response (corrective saccade) suggests peripheral vestibular dysfunction, which is reassuring 1
• A normal head impulse test in a dizzy patient raises concern for a central (stroke) cause 1, 3

Nystagmus Assessment

• Evaluates the direction and characteristics of spontaneous nystagmus 1
• Direction-changing nystagmus (changes with gaze direction) suggests a central cause and warrants urgent imaging 1, 3
• Unidirectional horizontal nystagmus suggests a peripheral cause 1
• Pure vertical nystagmus strongly suggests a central cause 3

Test of Skew

• Detects vertical misalignment of the eyes, which suggests a central lesion 1
• Performed by alternately covering and uncovering each eye while the patient fixates on a target, looking for vertical correction movements 1
• Presence of skew deviation indicates a central cause 3

Patient Selection: Who Should Receive HINTS

HINTS is specifically designed for patients with Acute Vestibular Syndrome (AVS), which requires ALL of the following features 1, 4:

• Acute, persistent (continuous, not episodic) vertigo or dizziness
• Spontaneous nystagmus present on examination
• Nausea and/or vomiting
• Head motion intolerance
• New gait unsteadiness or ataxia

A critical pitfall is using HINTS in patients with intermittent symptoms or without documented nystagmus - one study found 96.9% of patients who received HINTS in the ED did not meet proper criteria, most often because they lacked nystagmus or had intermittent symptoms 5. HINTS should never be used for episodic positional vertigo (like BPPV), which requires the Dix-Hallpike maneuver instead 5.

Diagnostic Accuracy and Clinical Performance

When Performed by Trained Specialists

• Sensitivity of 96.7% and specificity of 94.8% for detecting stroke 6
• More sensitive than MRI-DWI obtained within 24-48 hours of symptom onset (HINTS sensitivity 95.3% vs. MRI sensitivity 85.1%) 2, 4
• Substantially outperforms the ABCD2 stroke risk score (HINTS sensitivity 96.5% vs. ABCD2 sensitivity 61.1%) 4

When Performed by Emergency Physicians

The American College of Emergency Physicians and Society for Academic Emergency Medicine state that most emergency physicians have not received adequate training to perform HINTS with sufficient accuracy as a first-line test before MRI 7, 1. A meta-analysis found that when performed by emergency physicians in isolation, sensitivity dropped to 83% and specificity to only 44% 6. Subspecialists achieve significantly higher specificity (97.6%) compared to non-subspecialists (89.1%) 2.

Enhanced HINTS: The HINTS-Plus Exam

For patients with suspected anterior inferior cerebellar artery (AICA) stroke, add bedside hearing testing to create "HINTS-Plus" 2. Standard HINTS has lower sensitivity for AICA strokes (84.0%) compared to posterior inferior cerebellar artery (PICA) strokes (97.7%), but adding acute hearing loss assessment increases sensitivity to 99.2% 2.

Additional Clinical Considerations

Severe Gait Instability

• Severe (grade 3) truncal ataxia or inability to walk has 99.2% specificity for central causes but only 35.8% sensitivity 2
• Severe imbalance disproportionate to vertigo suggests cerebellar involvement and warrants imaging 3

High-Risk Features Requiring Imaging Regardless of HINTS

• Age over 50 years with vascular risk factors (hypertension, diabetes, smoking, atrial fibrillation) 1, 3
• Focal neurologic deficits (diplopia, dysarthria, dysphagia, limb weakness) 3
• New severe headache or neck pain 7

Critical Caveat About "Normal" Neurologic Exams

Up to 75-80% of patients with acute vestibular syndrome from posterior circulation stroke lack focal neurologic deficits on standard examination 1, 3. This is why HINTS is valuable - it can identify stroke even when the traditional neurologic exam appears normal 1.

Imaging Recommendations Based on HINTS Results

• If HINTS suggests a central cause (normal head impulse, direction-changing nystagmus, or skew deviation), urgent MRI with diffusion-weighted imaging is indicated 1, 8
• MRI is superior to CT for detecting posterior circulation stroke 8
• If performed by non-expert examiners in the emergency department, do not rely on HINTS alone to exclude stroke - proceed with MRI for high-risk patients 7, 1