Variations of biphasic head shake response: physiology and clinical significance

Is There an “Acquired Idiopathic Head-Shaking Nystagmus”?—A Discussion of Mechanisms and Clinical Implications Based on a Case Report

Background

Head-shaking nystagmus (HSN) occurs in both peripheral and central vestibular disorders. In most cases, HSN can be attributed to an asymmetric peripheral vestibular input or a structural lesion mostly in the cerebellum affecting the central velocity storage mechanism. An isolated HSN is very rare.

Case Presentation

We report on a young female patient with the clinical picture of recurrent episodes of vertigo, which were induced by fast head movements and were accompanied by a severe right-beating HSN with a long time constant of 60 s. There was no other clinical and instrument-based evidence of peripheral vestibular dysfunction (including video head impulse test, caloric test, vestibular-evoked myogenic potentials) or indication of a structural lesion in the nodulus, uvula or pontomedullary brainstem on fine-slice magnetic resonance imaging. She had no previous history of migraine, hearing deficits, or other focal neurological symptoms. Diagnostic criteria for vestibular paroxysmia, vestibular migraine, benign peripheral paroxysmal vertigo, or any other known vestibular disorders were not fulfilled. Chart review in the database of the German Center for Vertigo and Balance Disorders indicated eight additional patients with a similar clinical phenotype between 2018 and 2022.

Conclusion

We propose a clinical entity called acquired idiopathic head shaking nystagmus (aiHSN) as a rare cause of episodic vertigo induced by fast head movements. Nystagmus characteristics suggest a subtle functional pathology of the central velocity storage mechanism in the nodulus and uvula, which is exacerbated during symptomatic episodes.

Caractérisation du test vibratoire. Comparaison avec les résultats du « Head shaking test »

OBJECTIVES

The purpose of this work was to study the complementary contribution of the vibratory test (VT), the head shaking test (HST) and the caloric test (CT) in patients with total or partial vestibular lesions. We investigated the usefulness of these three tests, particularly the high frequency VT, for multiple-frequency vestibular study.

MATERIALS AND METHODS

The study cohort included 40 patients with total vestibular lesions (TVL) and 47 patients with partial vestibular lesions (PVL), the latter group including 21 patients with recent Menière disease, 15 with sudden-onset loss of vestibular function (SLVF), 5 with tumors of the cerebropontine angle, and six with diverse conditions. The HST protocol was 2 Hz stimulation (head speed greater than 180 degrees /s). The VT used an ABC 100 Hz vibrator operating at 0.8 mm and an S stimulator delivering frequencies between 30 and 115 Hz during 10 s stimulations. An LIVN-2 videoscope (biodigital France) and a 2D and 3D videonystagmograph (synapsis France) were used for the recordings. Mastoid stimulation was used for the VT.

RESULTS

For the 40 patients with TVL, the three tests (VT, CT, HST) were in agreement for all frequencies. The nystagmus produced by the VT demonstrated a horizontal component in 96% of the patients, a vertical component in 47%, and a rotational component in 30%. For the 47 patients with PVL, 9 of the 21 with Menière disease had a normal CT. Conversely, nystagmus was triggered by the HST in 10 and by the VT in 6. Nystagmus triggered by the VT and the HST was non-coherent with opposing direction in two-thirds of the patients. In certain cases, the VT demonstrated a variation in the direction of the nystagmus depending on the stimulation frequency, 30 or 100 Hz. Among the 15 patients with SLVF, the HST triggered nystagmus in only 5 and the VT in 14 (5 patients had nystagmus non-coherent with the side of the lesion). For the 5 patients with tumors of the cerebropontine angle (small neuroma or meningioma), the CT was negative in all 5, the HST was negative in 3, and the VT demonstrated lesional nystagmus in 4. Looking at the overall results, in the 47 patients with PVL (including 21 cases of Menière disease outside an acute phase) the CT demonstrated significant hypovalence in 70%, while the nystagmus demonstrated asymmetrical response in 44% when triggered by the HST and in 85% when triggered by the VT.

CONCLUSION

The VT is less invasive than the HST, particularly for elderly patients with osteoarthritis. It would be interesting in patients with bilateral tympanic perforation since the CT cannot be performed. It can reveal vestibular asymmetry. For unilateral partial vestibular lesions, the VT triggers nystagmus more often than the HST. It is particularly sensitive between acute episodes in patients with Menière disease. A discordance between the direction of the nystagmus triggered by the HST and the VT is particularly frequent in patients with labyrinthine hydropsis who exibit a normal CT. In certain cases of apparent bilateral areflexia to the CT for low frequencies, the VT can disclose vestibular asymmetry for high frequencies. The nystagmus triggered by the VT begins and ends with stimulation with little or no tiring. The nystagmus triggered by the HST occurs after the stimulation and depends on the frequency of the head shaking. Thus, the HST (2 Hz and its harmonics), the VT (100 Hz) and the CT (<0.01 Hz) all make significant contributions to multiple-frequency analysis of vestibular function, particularly useful in patients with partial vestibular lesions. These tests probably solicit cells with different topographies or different frequency sensitivities.

Prevalence of post-headshake nystagmus in patients with caloric deficits and vertigo

Post-headshake nystagmus (PHN) has recently been described as a clinically useful physical sign implying uncompensated asymmetric input from the vestibular end organs. A rapid 20-second headshake and sudden stop produces a jerk nystagmus of 5- to 20-second duration in certain individuals with symptoms suggestive of a peripheral vestibulopathy. This retrospective review of 214 patient evaluations was undertaken to study the associations between post-headshake nystagmus, caloric deficits after bithermal binaural irrigation, and the presence of vertigo. Both clinical observation of the nystagmus with eyes open (PHN-OBS) and routine EOG recording with eyes closed (PHN-EOG) were used. In patients with unilateral caloric deficits, 42% (18 of 43) had PHN-EOG, compared with 18% (3 of 17) in patients with bilateral dysfunction and 15% (23 of 154) in patients with normal calorics (p less than 0.001). In similar fashion, 26% (32 of 124) of patients with vertigo (recent or past) had PHN-EOG compared to 13% (12 of 90) of patients without vertigo (p less than 0.03). Finally, of 110 cases with both PHN-EOG and PHN-OBS performed, 45% (9 of 20) with PHN-EOG also had PHN-OBS, as opposed to only 4% (4 of 90) without PHN-EOG displaying PHN-OBS (p less than 0.0001). We conclude that the prevalence of post-headshake nystagmus is increased in patients with either a unilateral caloric deficit or a history of true vertigo, and is best detected in the absence of vision.