Head-shaking nystagmus (HSN) is another method of detecting an imbalance of dynamic vestibular function1.
Firstly, with Frenzel goggles in place, the patient should be instructed to shake their head vigorously but carefully from side to side, about 30 times at about 2 Hz. The chin should be pitched slightly down (to put the planes of the horizontal semicircular canals in the plane of head rotation).
The examiner should look for any nystagmus following the headshaking.
- Normal individuals have, at most, a beat or two of headshaking nystagmus.
- With a unilateral loss of labyrinthine function there will usually be a vigorous nystagmus characterised by slow phases directed initially towards the lesioned side, which decays over 20 seconds, and which is then followed by a reversal phase with slow phases directed towards the intact side.
- Ipsiversive head-shaking nystagmus (with the fast phase beating toward the lesioned ear) has been described in lateral medullary infarction2.
The initial phase of headshaking nystagmus arises because there is an asymmetry of peripheral inputs during high velocity head rotations; a larger amplitude response is transmitted centrally during rotation towards the intact side than towards the affected side, since excitatory vestibular inputs are more effective than inhibitory ones (Ewald's second law). This asymmetry leads to an accumulation of activity during the headshaking within the vestibular nuclei in the velocity storage mechanism. The nystagmus following headshaking in patients with a vestibular imbalance reflects the decay of activity within the velocity storage mechanisms.
Central lesions, for example due to cerebellar dysfunction, may also lead to headshaking nystagmus, often with a vertical nystagmus appearing after horizontal headshaking (so-called cross coupled nystagmus).
Finally, headshaking nystagmus can probably arise from mechanical disturbances in the labyrinth, eg, from a perilymph fistula.
(vv)Head_Shaking_Nystagmus.mp4(tt)
(vv)HSN2.mp4(tt)
From: Halmagyi GM. Clinical Examination of the Vestibular System. J Vestib Res. Teaching Course, 29th Bárány Society Meeting, Lecture 2, June 5, 2016, Seoul, Korea.
From: https://www.youtube.com/watch?v=ehR7SOlBBow
Patient video also shown here: central positioning nystagmus (due to a lesion of the nodulus)
(vv)HSNZee.mp4(tt)
From: Zee DS. The cerebellum for the neuro-ophthalmologist: A video tutorial of some signs and syndromes to recognize NANOS 42nd Annual Meeting 2016. Retrieved from: https://collections.lib.utah.edu/ark:/87278/s6nw2r5g
(vv)HSNCerebellar.mp4(tt)
From: Zee DS. The cerebellum for the neuro-ophthalmologist: A video tutorial of some signs and syndromes to recognize NANOS 42nd Annual Meeting 2016. Retrieved from: https://collections.lib.utah.edu/ark:/87278/s6nw2r5g