Cervical afferent pathway to inferior oblique motoneuron in the cat

Skull vibration-induced nystagmus in vestibular neuritis

BACKGROUND

As described by Dumas, an 80-100 Hz vibration applied to the mastoid produces a horizontal nystagmus, with quick phases beating away from the affected side in patients with unilateral vestibular loss (UVL).

AIM/OBJECTIVES

To elucidate the characteristics of skull vibration-induced nystagmus (SVIN) in patients suffering from vestibular neuritis and how these characteristics are related to information provided by the video head impulse test (vHIT).

MATERIAL AND METHODS

Sixty-three patients were enrolled to perform a vHIT to measure the gain in both ears. SVIN was induced with stimulation at 30 Hz, 60 Hz, and 100 Hz. The slow phase velocity (SPV) of the SVIN was measured.

RESULTS

The SVIN test was positive in 25/63 patients at 30 Hz, 36/63 at 60 Hz and 46/63 at 100 Hz. Mean gain difference between both ears to obtain a positive SVIN at 30 Hz was observed to be 0.38 ± 0.25, decreasing to 0.35 ± 0.23 at 60 Hz, and 0.31 ± 0.24 at 100 Hz (p = .025). We found a significant positive linear correlation between the gain asymmetry measured using horizontal vHIT and SPV in SVIN at 100 Hz.

CONCLUSIONS AND SIGNIFICANCE

There is a close relationship between the difference in the gains of both ears as measured using VHIT and the SPV of the nystagmus induced by SVIN at 100 Hz.

Assessing the cervico-ocular reflex system via modifying the ocular vestibular-evoked myogenic potential test

PURPOSE

The aim of this study was to devise a novel test for assessing the cervico-ocular reflex (COR) system via head vibration (termed h-COR) or neck vibration (termed n-COR) method.

MATERIALS AND METHODS

Thirteen patients with complete loss of bilateral vestibulo-ocular reflex (VOR) showing oscillopsia were assigned to Group A, while 13 patients with bilateral VOR loss but no oscillopsia were Group B. Another 13 healthy elderly served as a control. The COR test was performed via modifying the ocular vestibular-evoked myogenic potential (oVEMP) test by tapping at the forehead with head rotation (h-COR) or at mid-dorsal neck with head straight (n-COR).

RESULTS

Both h-COR and n-COR tests displayed similar cI-cII waveforms. None of the Group A or healthy elderly showed present h-COR, while 8% of Group A and 31% of the healthy elderly revealed present n-COR. In contrast, present h-COR and n-COR were elicited in 85 and 77% of Group B, respectively. Restated, significantly higher response rate of COR in Group B (without oscillopsia) than Group A (with oscillopsia) indicates that present COR is related to the alleviation of oscillopsia.

CONCLUSIONS

Head vibration method (h-COR test) is superior to neck vibration method (n-COR test) for assessing the COR system.

Mechanisms of Vibration-Induced Nystagmus in Normal Subjects and Patients with Vestibular Neuritis

It has been reported that vibration applied either on the mastoid or on the sternocleidomastoid (SCM) muscles induces nystagmus in normal subjects or patients after unilateral vestibular neuritis (VN). The aims of the study were to characterize vibration-induced nystagmus (VIN) in normal and patient groups and to propose the mechanism of VIN. We recorded eye movements during unilateral 100-Hz vibration on the mastoid bone and SCM muscles in 22 normal subjects and 19 patients with unilateral VN. In normal subjects, the direction of slow-phase velocity (SPV) tended to be toward the vibrated side. Vibration on the right/left SCM muscles induced mean SPV of 1.7 degrees/s, -1.9 degrees/s toward the stimulated side in all normal subjects. Vibration on the right/left mastoid bone induced mean SPV of 1.5 degrees/s, -0.4 degrees/s toward the stimulated side in most of the normal subjects. Positive value means SPV to the right side. This directional preponderance to the vibrated side was statistically significant. Among the patients with VN, the slow phase of the VIN was directed towards the lesioned side, irrespective of whether vibration was applied on the lesioned or intact side. Vibration on the right/left mastoid bone induced mean SPV of -10.4 degrees/s, -10.8 degrees/s toward the lesioned side. Vibration on the right/left SCM induced mean SPV of -7.9 degrees/s, -10.5 degrees/s toward the lesioned side. The amplitude of SPV showed a significant correlation with the unilateral weakness of caloric test. Our results suggest that the proprioceptive stimulation plays a major role in producing VIN in normal subjects, while VIN is generated mostly by the vestibular stimulation in patients with unilateral VN, which helps us localize the lesion side. Vibration tests on the SCM muscles as well as on the mastoid are recommended and our hypothetic mechanisms of VIN are presented.

[Results of videonystagmographic (VNG) analysis in vestibular post-traumatic pathology]

From February 1998 to July 1999, 569 patients affected by vestibular disorders--following a whiplash injury and/or a cranial trauma--were studied. The neuro-otological examination included a tonal audiometry, brain stem auditory evoked potentials, clinical and instrumental vestibular tests (caloric test, rotatory test, assessment of visually guided eye movements). The study of eye movements was conducted with the support of the Ulmer video-oculographical system. The aim of the research was to analyse, both from a qualitative and a quantitative perspective, the vestibular and clinical findings. Particular emphasis was laid on the incidence of the "up-beating" nystagmus in different categories of patients, all supported by a statistical study. As a result, an etiopathogenetical hypothesis of the nystagmus was advanced, based on altered otolithic and cervical inputs. At the same time, the importance of the video-nystagmographical system was stressed, to the extent that it leads to a standardised and objective analysis, fundamental for clinical and forensic aspects.