Head Impulse Test

Micheal Halmagyi and Ian Curthoys described this simple and reliable bedside test that could be used for detecting persons with unilateral peripheral vestibular deficits in 1988.[1] It is also known as the Head Thrust Test. It works by testing the Vestibular Ocular Reflex (VOR).
VOR - a reflex that helps to correct the eye movement during any change in head position and to correct the eye movement rapidly so that vision remains on the target. [2]

Advantages of the test

- Relatively quick

- Can be used even on patients with acute Vertigo

- Can be repeated within a short time

How to do the test

Position of the Tester: Sitting
Position of the Subject: Sitting in front of the tester with eyes fixed on the examiner's nose or a distant target
Alternatively testing position: the tester can stand or sit behind the subject, but there needs to be a way to record the eye movement.
Precautions: The tester must ensure that the subject doesnot have any neck issues like Vertebro basilar insufficiency and neck range of motion is adequate
Expectation of the subject: The subject needs to keep their eyes focussed on the target during the testing procedure and avoid premature eye closure
Examiner action: The examiner moves the head quickly and unpredictably to 10 to 15 degrees of neck rotation[3], care needs to be ensured to avoid Cervical spine manipulation during the testing.
Normal response: Eyes remain on the target after the examiners movement
Abnormal response: Eyes are dragged off the target by the turning of the head, followed by a corrective saccade back to the target after the turning of head.

Inference

The corrective saccade indicates a deficient VOR on the same side of the head turn, indicating a peripheral vestibular lesion on the same side[4]. Use of Videonystagmography can help in the interpretation and :accuracy of this test.[5]
This test is reported to have a higher specificity (82 to 100 %) than sensitivity (34 to 39 %) [6-8]. In one report, flexing the head forward 30º during the test increased sensitivity to as high as 71 to 84 %[9].

What is this test good for?

The HIT works well for the person with complete vestibular loss, wheres it is less sensitive to a person with mild to moderate loss of function[10]. About 50% of the canal paresis is needed for the test to be positive[11].

References

[1]. Halmagyi GM, Curthoys IS. A clinical sign of canal paresis. Arch Neurol (1988) 45:737–9
[2]. Kuo CH, Pang L, Chang R. Vertigo - part 1 - assessment in general practice. Aust Fam Physician. 2008;37(5):341-7
[3]. S. Curthoys & L. Manzari (2017) Clinical application of the head impulse test of semicircular canal function, Hearing, Balance and Communication, 15:3, 113-26
[4]. Halmagyi GM, Cremer PD. Assessment and treatment of dizziness. J Neurol Neurosurg Psychiatry 2000; 68:129.
[5]. MacDougall HG, Weber KP, McGarvie LA, et al. The video head impulse test: diagnostic accuracy in peripheral vestibulopathy. Neurology 2009; 73:1134.
[6]. Harvey SA, Wood DJ, Feroah TR. Relationship of the head impulse test and head-shake nystagmus in reference to caloric testing. Am J Otol 1997; 18:207.
[7]. Harvey SA, Wood DJ. The oculocephalic response in the evaluation of the dizzy patient. Laryngoscope 1996; 106:6.
[8]. Beynon GJ, Jani P, Baguley DM. A clinical evaluation of head impulse testing. Clin Otolaryngol Allied Sci 1998; 23:117.
[9]. Schubert MC, Tusa RJ, Grine LE, Herdman SJ. Optimizing the sensitivity of the head thrust test for identifying vestibular hypofunction. Phys Ther 2004; 84:151.
[10]. Beynon, G. J., P. Jani, et al. "A clinical evaluation of head impulse testing." Clin Otolaryngol Allied Sci 1998; 23(2): 117-22.
[11]. Hamid, M. "More than a 50% canal paresis is needed for the head impulse test to be positive." Otol Neurotol 2005; 26(2): 318-9.