What is the purpose and interpretation of the HINTS (Head Impulse Test, Nystagmus assessment, and Test of Skew) exam in patients with suspected stroke or vertigo?

The HINTS Exam: Purpose and Interpretation in Suspected Stroke or Vertigo

The HINTS (Head Impulse, Nystagmus, Test of Skew) examination is a powerful bedside diagnostic tool that can differentiate between central and peripheral causes of vertigo with greater sensitivity than early MRI for detecting stroke when performed by properly trained clinicians. 1

Components of the HINTS Exam

• Head Impulse Test: Assesses the vestibulo-ocular reflex. The examiner rapidly turns the patient's head while the patient fixates on a target. An abnormal response (corrective saccade after head movement) suggests peripheral vestibular dysfunction, while a normal response in a dizzy patient raises concern for a central cause 1

• Nystagmus Assessment: Evaluates the direction and characteristics of nystagmus. Direction-changing nystagmus suggests a central cause, while unidirectional horizontal nystagmus that increases when looking in the direction of the fast phase suggests a peripheral cause 1

• Test of Skew: Detects vertical misalignment of the eyes, which suggests a central lesion. The examiner covers and uncovers each eye while the patient fixates on a target, looking for vertical correction movements 1

Clinical Application

• The HINTS exam is specifically designed for patients with Acute Vestibular Syndrome (AVS) - characterized by acute, persistent vertigo with nausea/vomiting, head motion intolerance, nystagmus, and gait unsteadiness 1

• When properly performed in appropriate patients, HINTS has shown remarkable diagnostic accuracy:

  • Sensitivity of 96.5% and specificity of 84.4% for detecting stroke 2
  • Outperforms the ABCD2 stroke risk score in AVS patients 2
  • More sensitive than early MRI (100% vs 46%) when performed by specialists 1

Interpretation of Results

• "HINTS peripheral" (normal head impulse, direction-fixed horizontal nystagmus, no skew) suggests a peripheral cause like vestibular neuritis 1, 2

• "HINTS central" (abnormal head impulse, direction-changing nystagmus, or presence of skew deviation) suggests a central cause such as stroke 1, 2

• The term "HINTS negative" should be avoided as it is ambiguous 3

Important Caveats and Limitations

• Examiner expertise matters significantly:

  • Subspecialists achieve higher specificity (97.6%) compared to non-subspecialists (89.1%) 4
  • Emergency physicians often use the test incorrectly or interpret results ambiguously 5, 3

• Patient selection is critical:

  • HINTS is validated only for AVS patients (continuous vertigo with nystagmus) 5
  • Should not be used for episodic vertigo or combined with Dix-Hallpike (which tests for BPPV) 5

• Stroke location affects sensitivity:

  • Lower sensitivity for anterior cerebellar artery strokes (84%) compared to posterior inferior cerebellar artery strokes (97.7%) 4
  • Adding bedside hearing tests ("HINTS plus") improves detection of anterior circulation strokes 4

• Timing considerations:

  • Most validation studies performed HINTS within 24 hours of symptom onset 6
  • Early MRI (within 24-48 hours) can be falsely negative in up to 15% of strokes 2

Clinical Decision Making Algorithm

1. Determine if patient has true AVS:

   • Acute, persistent vertigo (not episodic)
   • Presence of nystagmus
   • Associated symptoms: nausea/vomiting, head motion intolerance, gait unsteadiness 1, 5

2. Perform complete HINTS examination:

   • Document all three components properly
   • Use proper terminology ("HINTS central" or "HINTS peripheral") 3

3. Interpret results based on stroke risk:

   • High-risk patients (multiple vascular risk factors) have up to 75% risk of stroke with AVS 1
   • Even with normal neurological exam, 11% of AVS patients may have acute infarct 1

4. Consider imaging appropriately:

   • If HINTS suggests central cause → urgent MRI (preferred) or CT
   • If HINTS performed by non-specialists → consider MRI even with peripheral pattern 1
   • If HINTS performed by specialists and suggests peripheral cause → imaging may be deferred 1

Conclusion

The HINTS exam is a valuable clinical tool that, when properly performed and interpreted, can help identify patients with vertigo due to stroke even when traditional neurological examination is normal. However, its accuracy depends heavily on examiner expertise and proper patient selection.