Vestibulo-sympathetic reflex in patients with bilateral vestibular loss

This study assessed cardiovascular control during head-down neck flexion (HDNF) in a group of patients suffering from total bilateral idiopathic vestibular loss (BVL) for 7 ± 2 yr. Nine adult patients (age 54 ± 6 yr) with BVL were recruited. Calf blood flow (CBF), mean arterial pressure (MAP), and heart rate (HR) were measured with subjects' eyes closed in two lying body positions: ventral prone (VP) and lateral (LP) on the left side. Vascular resistance (CVR) was calculated as MAP/CBF. The HDNF protocol consisted in passively changing the head position: head up (HU)-head down (HD)-HU. Measurements were taken twice at each head position. In VP CBF significantly decreased in HD (3.65 ± 0.65 mL·min^-1·100 mL^-1) vs. HU (4.64 ± 0.71 mL·min^-1·100 mL^-1) (P < 0.002), whereas CVR in VP significantly rose in HD (31.87 ± 6.93 arbitrary units) vs. HU (25.61 ± 6.36 arbitrary units) (P < 0.01). In LP no change in CBF or CVR was found between the two head positions. MAP and HR presented no difference between HU and HD in both body positions. Age of patients did not significantly affect the results. The decrease in CBF of the BVL patients was similar to the decrease observed with the same HDNF protocol in normal subjects. This suggests a sensory compensation for the lost vestibular inputs that could originate from the integration of inputs from trunk graviceptors and proprioceptive and cutaneous receptors. Another possibility is that the HDNF vascular effect is evoked mostly by nonlabyrinthine sensors.NEW & NOTEWORTHY The so-called vestibulo-sympathetic reflex, as demonstrated by the head-down neck flexion (HDNF) protocol, is present in patients with total bilateral vestibular idiopathic loss, equally in young and old subjects. The origin of the sympathetic effect of HDNF is questioned. Moreover, the physiological significance of the vestibulo-sympathetic reflex remains obscure, because it acts in opposition to the orthostatic baroreflex. It may serve to inhibit the excessively powerful baroreflex.

Late and sudden recovery of sudden deafness or vestibular neuronitis

INTRODUCTION

Vestibular neuronitis (VN) and sudden deafness (SD) are well-defined entities. The abrupt appearance of symptoms in both disorders represents an important element for the diagnosis. In cases of VN, symptoms regress gradually over time as the peripheral function recovers, or the central nervous system compensates for the balance deficit. In cases of SD, the recovery occurs in about half the cases and is generally progressive. The chances to recover normal levels of hearing are better if the recovery occurs early after the onset of the deficit. The goal of the paper is to present new insights of these disorders based on four unusual cases and on an evaluation of the delay for the function's recovery.

MATERIAL AND METHODS

1) We report two cases of VN and two of SD whose the recovery was late and sudden; 2) The recovery time after a SD was retrospectively analysed using the chart of 36 patients seen<or=24 hours after the onset of the deficit, who recovered hearing, and who had undergone at least one audiogram per month up to 6 months after the deficit, whether treated or not.

RESULTS

Twenty-eight patients recovered hearing within 6 months following the deficit. In eight patients, an audiogram was performed months later and showed a normalization of hearing. In these patients, the exact time of the recovery remained unknown.

CONCLUSION

A few patients may recover their inner ear function more than 6 months after the deficit. The recovery of function after SD or VN does not always follow the generally accepted pattern, as it can be late and sudden. These observations raise new questions to the hypothetical etiologies of SD and VN.

[Exploration of the otolith function]

The analysis of our vertiginous patients reveals that the likely existence of a pattern of symptoms related to a disturbance of the otolith organ responsible for detection of linear accelerations. Very often otolith pathology affects only certain directions of movement or tilting in relation to gravity. The various tests of the otolith function do not seem to identify all of these otolith deficits. It is possible that each individual test explores only partially the 4 otolith organs. Our otolith tests are still either too general, or, only focused on a part of a multi-directional function (and wrongly emphasizing a partial pathology). Thus, the history remains the finest diagnostic tool. The exploration of the otolith function has improved. These tests are not redundant. The subjective visual vertical tests the otolith function up to the vestibular cortex whilst the off-vertical axis rotation (OVAR) test explores the ocular otolith reflex. The myogenic otolith evoked potentials are saccule-collic. The cerebral cartography shows the various zones of cortical saccular activity and the tilt suppression test explores a reflex involving the cerebellar nodulus. However all of these tests are still nonspecific. There 'non-specificity' is similar to the non-specific nature of a free field hearing or the rotatory vestibular tests. The analysis of patient symptoms, using diagrams summarizing the principal clinical findings, or using a 3D software, facilitates the identification of the involved side, the affected organ (utricle or saccule) and to some extent the possible site of the lesion (just as a visual field would assist in identification of the retinal area affected prior to fundoscopy). Some otolith tests can be very sensitive albeit non-specific like the subjective visual vertical test. Others are more specific in identification of the organ and side affected like the otolith sacculo-collic evoked potentials. The choice of vestibular function tests is best based on the patient's particular symptoms. Thus a patient complaining of falling outwards is to be tested by offset rotations. A patient complaining of falling while going down in a lift is best investigated by the cortical vestibular otolith evoked potentials.

The responses of frogs to vestibular and visual stimulation in weightlessness

The authors, using rotatory visual and vestibular stimulators, propose to perform an experiment to study the effect of long periods of weightlessness on vestibular and visual interactions in frogs. The results will be analysed within the Framework of sensory conflict theory. Preliminary experiments are in progress in order to determine the best method for containments of long duration.

Nonlinear analysis of orthostatic posture in patients with vertigo or balance disorders

The stabilometry signals involve irregular and unpredictable components. In order to identify the hidden dynamics that underlie the multi-link networks consisted of the multiple sensory systems, motor components and central integration, we applied a nonlinear analysis to these signals. We evaluated the postural control differences between eyes open and closed by means of the dynamical closeness between two states, known as similarity index, for the patients with vestibular disorders. We were able to demonstrate that some patients (eight of 21) showed a difference between the conventional and nonlinear measures. Especially, the similarity index tended to reflect the clinical course of the vestibular compensation and the findings in the patients with benign paroxysmal positional vertigo (BPPV) demonstrated that its vestibular function may include various pathologies besides canalithiasis. These results suggest that nonlinear analysis can elucidate the complex postural control networks and this procedure may also be able to provide the new findings of the stabilometry examinations.

[Rotatory impulse test does not replace caloric tests]

We sought to determine whether the rotatory impulsional test was capable of exploring the canalar function with sufficient precision to replace the caloric test, as it has been recently affirmed. We first compared the observed preponderance from this test with that measured during a sinusoidal (20 and 4 s) test. We observed that, in the case of a significant preponderance for a given test, there was complete redondance with the preponderance observed with any other test. The rotatory impulsional test does not present any specific advantage compared to other kinetic test as far as the observation of the preponderance phenomenon. We then compared the preponderance with the results of the caloric tests and came to the following conclusions i) the absence of preponderance does not allow us to predict the absence of vestibular deficit, due to the fact that 37% of the deficits were compensated for including acoustic neuroma; ii) the presence of a preponderance does not allow a priori to say whether it is of vestibular, cervical, or central origin and systematic caloric tests shows that almost one fourth of preponderance observed is not associated with unilateral weakness iii) supposing that a clinical argument allow us to conclude as to the probable vestibular origin of a vestibular preponderance, the direction of this preponderance does not allow us to determine which side is involved. In fact, if the undercompensated deficits are 3 times more frequent than overcompensated deficits, the proportion of preponderance not linked to a significant deficit indicates that the probability of encountering a preponderance related to a specific undercompensated deficit is approximately 50%. We thus did not find in the rotatory impulsional test any specific advantage allowing us to predict the laterality of a vestibular lesion.

Unilateral vestibular neuritis with otolithic signs and off-vertical axis rotation

Off-vertical axis rotation (OVAR) at constant velocity is a dynamic otolith stimulus that induces horizontal and vertical eye movement responses. To determine the value of this examination as a test for unilateral otolithic hypofunction, we compared the OVAR responses of patients suffering from acute vestibular neuritis (VN) without any sign of otolith affection, with those of patients suffering from acute VN with otolithic signs. The horizontal eye movement bias component shows directional preponderance (DP) significantly higher in patients with otolithic signs than in patients not presenting them. However, as bias DP also reflects the imbalance between right and left horizontal canals activity, this greater bias DP could be explained by the more severe canals impairment-evaluated by caloric test-found in patients with otolithic signs. No significant difference can be shown on horizontal modulation. The DP of vertical modulation is significantly higher in patients presenting otolithic signs than in patients not presenting them: in the case of otolithic signs, the responses are smaller during rotations toward the affected side. Therefore, this variable could be used as an indication of unilateral otolithic hypofunction.

Unilateral peripheral semicircular canal lesion and off-vertical axis rotation

Off vertical axis rotation (OVAR) is a stimulus that can be used to assess the otolith-ocular reflex. However, experimental data suggest that isolated unilateral lesion of the lateral semicircular canal (SCC) nerve could modify responses to OVAR. Thus, to determine what nystagmus variables are not affected by SCC dysfunction and might be used as indices of otolithic disease, responses to OVAR were compared in 39 healthy controls and in 19 patients suffering from acute unilateral vestibular neuritis (VN), without any sign of otolith dysfunction. Horizontal and vertical slow phase velocities (SPV) were measured during earth vertical axis rotation (EVAR), and during OVAR at a tilt angle of 9 degrees and rotation velocity of 60 degrees/s. During OVAR, horizontal SPV consists of a sinusoidal modulation superimposed on a sustained bias opposite to the rotation. Vertical SPV consists of a sinusoidal modulation without bias. In patients, the bias shows directional preponderance (DP) toward the healthy side, strongly correlated to EVAR nystagmus DP. It would therefore simply reflect an imbalance, produced by the unilateral peripheral vestibular lesion, between right and left vestibular nuclei activity. On the other hand, vertical and horizontal modulations are not significantly different in patients and controls. Since the cause and the site of VN are not known, we cannot be sure that patients had pure SCC deafferentation. However, as all of them had SCC paresis it is concluded that OVAR modulations are not affected by a strong dysfunction of the pathways issued from the SCCs.

[Vertigo in children]

Oto-neurologic investigation in the child with vertigo is fundamentally important. In 3% of cases, it reveals the presence of a cerebral tumour. Technical difficulties in examining a child under 5 years of age stem from their fear of the dark, insecurity in a medical setting and a labile attention span. Major causes are migraine (in 28% of cases) and childhood idiopathic paroxysmal vertigo, and recurring vestibular disorders (13% of cases). Classic disorders such as Ménière's disease are rare in the child (3% of cases), as are benign paroxysmal positional vertigo and cupulolithiasis (only 5% of children with vertigo).

Orthostatic postural control in vestibular neuritis: a stabilometric analysis

Posturographic data for 182 vestibular neuritis patients were recorded on a static posturographic platform (stabilometry) with the patients' eyes both open and closed. Three of the parameters studied are presented here: mean position of the center of pressure, area of the statokinesigram, and Romberg's quotient. Vestibular neuritis modifies the performance of the fine-postural system in unpredictable ways, varying with the subject. It may disturb either the mean position of the center of pressure or the integration of visual input. Sixty of the patients in this study did not use visual input to stabilize their position in relation to their surroundings. The value of stabilometry as a method for observing the integration of visual input in the control of orthostatic posture is discussed.

Menière's disease in children

Fourteen children (aged 14 years or younger) with typical Ménière's triad with cochlear sensorineural hearing loss, tinnitus, and intermittent vertigo attacks lasting from minutes to hours were investigated in four different neuro-otologic centers. Nine children, labeled as having "idiopathic Ménière's disease," developed the auditory and vestibular symptoms without any detectable causative factor. Five children, labeled as suffering from "secondary Ménière's syndrome," had histories of an initial hearing loss following mumps, hemophilus influenza meningitis, temporal bone fracture, or congenital or embryopathic complications in the ear that developed into the full Ménière's triad 5 to 11 years later. The 14 children represent 1% of all cases affected with idiopathic or secondary Ménière's disease (or syndrome) that have been detected during the past five years in the four collaborating centers.

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity. This phase lead is smaller in albino than in pigmented rats. 2. Presence of vision (VVS) improves the phase angle of the VOR in both strains, especially at low frequencies. In pigmented rats the VOR is perfectly compensatory with respect to phase at all frequencies whereas in albinos the eye velocity still leads the head velocity. 3. There is no difference in the response characteristics of vestibular nuclear neurons (VN) to VS between albino and pigmented rats which could explain the difference in their VORs. 4. In the pigmented rat, there is a strong optokinetic input to VN which provokes a shift of the response peak towards peak head velocity. These visual-vestibular interactions at VN level are in agreement with the changes in the phase angle of the VOR. 5. In albino rat, there are no differences in the response characteristics of VN between VS and VVS, thus the decrease of the VOR phase lead observed in VVS compared to VS is due either to visual-vestibular interactions outside of the vestibular nuclei or to some general arousing effect of light. 6. Recording of responses of pretectal neurons to visual stimulation in albino rats has shown that they are activated in a phasic or tonic way by light on ("On cells") or off ("Off cells"). Contrary to the pigmented rat, pretreated neurons in albino exhibited no detectable direction specific optokinetic responses.

Status of vestibular function after prolonged bedrest

6 young, healthy, male volunteers were submitted to one week of head down (-4 degrees) bedrest. This position simulates the cerebral hemodynamic conditions in weightlessness. Measurements of vestibular equilibrium and of oculomotor system function were made before and after the prolonged bedrest. Analysis of the results indicates that vestibular responses, as measured by the maximal speed of the slow phase of the provoked nystagmus (caloric and sinusoidal rotatory stimulations), are decreased after prolonged bedrest. This statistically significant diminution requires confirmation with a greater number of cases. The reflex conflicting or interacting with the cervico-ocular and optokinetic reflexes on the one hand and the foveal vision on the other, is one of several possible explanations for the observed changes.

[Pseudocaloric nystagmus (author's transl)]

The effect of bithermal caloric tests on the velocity of spontaneous nystagmus was retrospectively studied in 107 patients with unilateral vestibular areflexia. In 35 out of 107 patients, the velocity or pre-test nystagmus was not lower than 15 jerks in 30 seconds. In our series, spontaneous nystagmus before the caloric test was mostly seen in patients with neuritis or sudden deafness, and as a rule, the tests had little effect on the velocity of the nystagmus. In 7 out of 10 cases of areflexic Mènière's disease spontaneous nystagmus was revealed by caloric tests. Spontaneous pre-test nystagmus was present in 6 out of 29 cases of neurinoma; its velocity was always reduced during the caloric tests. In 14 out of 25 cases of head injury, areflexia was usually compensated. Vestibular compensation can now be defined as the absence of vertigo, of spontaneous nystagmus before and after caloric tests and directional predominance.

[Rebound nystagmus: a new cerebellar sign (author's transl)]

Rebound nystagmus is a special type of nystagmus provoked by excentration of gaze of a sight (gaze nystagmus). Gaze nystagmus is absent when looking straight ahead, and is already clearly evident after excentration of gaze of less than 20 degrees. It beats in the direction of the excentration. The first special feature of rebound nystagmus is the fact that it disappears in 10 to 20 seconds. Its diagnostic significance could be based upon this feature alone, as was though up to now. However, its second original feature is fundamental. After excentration, gaze is brought back to the primary position (straight ahead). As confirmed by all the literature its value is of being pathognomic of a lesion of the cerebellar pathways. It is of the greatest simplicity, and it is sough by asking the subject to follow the finger of the examiner.

[Study on the nature of tonic ocular movement produced during pendular vestibular stimulation (author's transl)]

During vestibular function tests using the pendulum chair, electronystagmography has repeatedly shown that a tonic ocular deviation precedes the change in nystagmus. This tonic movement may be anticipated in respect to the change in the sinusoidal movement of the chair. Greiner, Conraux, Collard and more recently J.B. Causse, have proposed a hypothesis based on the own periodicity of the vestibular system. J. Max explained this phenomenon in terms of a difference in phase with the electronic system. Our investigation suggests another explanation of this phenomenon. Each half-period consists of a acceleration phase and a decelaration phase. Thus within half-period alone there are two successive forms of nystagmus induced. The succession of half-periods gives the usual systagmus response. We consider that the tonic response of the eyes is not an anticipated one in respect to the change in sinusoidal movement of the chair, but rather a delayed one in respect to the reversal in the direction of acceleration.

[Ocular fixation test in pendular vestibular stimulation. Hearing and balance laboratory (author's transl)]

The effects of ocular fixation on per-rotatory nystagmus were studied during the course of the pendular vestibular stimulation test. If the subject is normal, or the disorder is peripheral, the nystagmus is abolished. Examples of these different results are presented.