HINTS (head-impulse-nystagmus-test-ofskew)

NICE suggest that (1):

• for adults with sudden-onset acute vestibular syndrome (vertigo, nausea or vomiting and gait unsteadiness), a HINTS (head-impulse-nystagmus-test-ofskew) test should be performed if a healthcare professional with training and experience in the use of this test is available
  • for adults with sudden-onset acute vestibular syndrome who have had a HINTS test:
    • be aware that a negative HINTS test makes a diagnosis of stroke very unlikely
    • refer immediately for neuroimaging if the HINTS test shows indications of stroke (a normal head impulse test, direction-changing nystagmus or skew deviation)
      
      
  • refer immediately adults with sudden-onset acute vestibular syndrome in whom benign paroxysmal positional vertigo or postural hypotension do not account for the presentation, in line with local stroke pathways, if a healthcare professional with training and experience in the use of the HINTS test is not available
    
    

HINTS exam is an examination to differentiate clinically a central versus peripheral cause of vertigo. HINTS stands for Head Impulse, Nystagmus, and Test of Skew, and is a three-part oculomotor test. If any portion of the test indicates a central aetiology, the test is considered positive and further evaluation for stroke (or other central pathology) is warranted. The three components of the exam are as follows:

1 Head Impulse

• patient stands in front of the examiner, with their head held between the examiners hands
  • patient is asked to fixate on the tip of the examiners nose, and their head is rotated 20-40 in each direction, before being rapidly brought back to neutral
    
    
  • with rapid low-amplitude rotation of the head toward the midline, the patient's eyes should remain fixed on the target - normal response, which is preserved in posterior stroke
    
    
    • in peripheral causes of vertigo, the vestibule-ocular reflex is disrupted, and so they lose eye contact and correct with a saccade
      • patients with peripheral vertigo will have abnormal (positive)
        
        
        • rapid rotation of the head toward the affected side will result in loss of fixation and movement of the eyes away from the target
          • followed by a corrective saccade as the subject looks back toward the target
          • observation of this corrective saccade is abnormal, and considered a positive test
    • with central vertigo
      • typically have a normal (negative) head impulse test
        • typically no corrective saccade in patients with central vertigo, in whom the vestibulo-ocular reflex usually remains intact
        • rarely the combination of a combined stroke and middle ear infarction, patients may have an abnormal head impulse test
          • in such a case then the central cause of vertigo will be revealed by one of three other findings: direction-changing nystagmus, skew deviation, or unilateral hearing loss

2 Nystagmus

• patient is asked to look straight ahead, to the left, and to the right, while the direction of nystagmus is observed
  • nystagmus due to a peripheral cause is always horizontal, and will always have the fast phase in the same direction, and is often accentuated when the patient looks in the direction of the fast phase
    • if peripheral vertigo
      • will result in unidirectional, horizontal nystagmus
        • common to have a horizontal-beating nystagmus with a fast phase that is unidirectional
          • beats away from the affected side, and increases in intensity when the patient looks in the direction of the fast phase
            
            
  • any vertical or rotational element, or if the direction changes with direction of gaze, is suggestive of a central cause of vertigo
    • if central vertigo
      • can have rotatory or vertical nystagmus, or direction-changing horizontal nystagmus
        • generally have horizontal-beating nystagmus, mimicking peripheral vertigo
          • direction of the fast phase may change on eccentric gaze, i.e. the fast phase beats in one direction when looking to left, and the opposite direction when looking to the right
            • direction-changing nystagmus does not occur if a peripheral cause

3 Test of Skew

• patient again stand in front of the examiner and is asked to fixate on the tip of their nose
  • eyes are alternately covered
    • in a central cause of vertigo, the vertical alignment of the eyes may be different, and a vertical corrective movement will be seen as the eye is covered and uncovered. In peripheral causes, this finding is absent.
• if central cause of vertigo then commonly will have a right-left imbalance in otolith (gravity-sensing) function, resulting in a vertical misalignment of the eyes (i.e. one eye's gaze slightly higher than the other

Video of practicalities and considerations when performing the HINTS examination

Notes:

• the exam should be performed only on patients with continuous vertigo
  • if not active, continuous vertigo, then vestibulo-ocular reflex will remain intact and head impulse testing will be normal, with no corrective saccade observed
    • will be the case in BPPV and in patients without vertigo - such a finding may suggest central pathology when not the case
      
      

Reference:

• NICE (May 2019). Suspected neurological conditions: recognition and referral
• Vertigo. RCEM Learning (accessed 8/5/2019)