Asymmetric Vestibular Function Research Articles

Agreement between the Skull Vibration-Induced Nystagmus Test and Semicircular Canal and Otolith Asymmetry.

How significant asymmetries in otolith organ function in the presence of symmetrical and asymmetrical semicircular canal function influence skull vibration-induced nystagmus testing (SVINT) has not been well described. The aim of the study is to examine the agreement between SVINT and caloric testing, ocular vestibular-evoked myogenic potentials (oVEMP), and cervical vestibular-evoked myogenic potentials (cVEMP) for detecting asymmetric vestibular function. This is a retrospective study of patients presenting with the chief complaint of vertigo, dizziness, or imbalance. A total of 812 patients were studied with a median age at testing of 59 years (interquartile range 46-70; range 18-93) and included 475 (59%) women. Either the monothermal warm caloric test or alternate binaural bithermal caloric test, oVEMP, and cVEMP tests were administered to all patients. All patients underwent the SVINT prior to vestibular laboratory testing. Agreement between tests categorized as normal versus abnormal was summarized using percent concordance (PC). Sensitivity and specificity values were calculated for SVINT compared with other tests of vestibular function. There was higher agreement between ipsilateral and contralateral SVINT with the caloric test (PC = 80% and 81%, respectively) compared with oVEMP (PC = 63% and 64%, respectively) and cVEMP (PC = 76% and 78%, respectively). Ipsilateral and contralateral SVINT showed higher sensitivity for the caloric test (sensitivity = 47% and 36%, respectively) compared with oVEMP (sensitivity = 26% and 21%, respectively), or cVEMP (sensitivity = 33% vs. 27%, respectively). Specificity of SVINT was high (>80%) for all assessments of vestibular function. The presence of SVIN is a useful indicator of the asymmetry of vestibular function between the two ears when making judgments about semicircular canal asymmetry but is less sensitive to asymmetries in otolith organ function.

Asymmetric Unilateral Vestibular Perception in Adolescents With Idiopathic Scoliosis.

The cause of Adolescent Idiopathic Scoliosis (AIS) remains unclear, but one proposed cause of AIS is asymmetric vestibular function and the related descending drive to the spine musculature. The objective of this study was to determine if asymmetric vestibular function is present in individuals with AIS. Ten individuals with AIS (8F, 2M) and 10 healthy age- and sex-matched controls were exposed to 10s-long virtual rotations induced by monaural or binaural electrical vestibular stimulation (EVS), and 10s-long real rotations delivered by a rotating chair. Using a forced-choice paradigm, participants indicated their perceived rotation direction (right or left) to stimuli of varying intensity. A Bayesian adaptive algorithm adjusted the stimulus intensity and direction to identify a stimulus level, which we called the direction recognition threshold, at which participants correctly identified the rotation direction 69% of the time. For unilateral vestibular stimuli (monaural EVS), the direction recognition thresholds were more asymmetric in all participants with AIS compared to control participants [(0.22–1.00 mA) vs. (0.01–0.21 mA); p < 0.001]. For bilateral vestibular stimuli, however, the direction recognition thresholds did not differ between groups for either the real or virtual rotations (multiple p > 0.05). Previous reports of semicircular canal orientation asymmetry in individuals with AIS could not explain the magnitude of the vestibular function asymmetry we observed, suggesting a functional cause to the observed vestibular asymmetry. Thus, the present results suggest that a unilateral vestibular dysfunction is linked to AIS, potentially revealing a new path for the screening and monitoring of scoliosis in adolescents.

Rebalancing the Vestibular System by Unidirectional Rotations in Patients With Chronic Vestibular Dysfunction.

Introduction: Vestibular dysfunction is a common disorder that results in debilitating symptoms. Even after full compensation, the vestibulo-ocular reflex (VOR) could be further improved by using rehabilitation exercises and visual-vestibular adaptation. We hypothesized that in patients with asymmetric vestibular function, the system could be rebalanced by unidirectional rotations toward the weaker side (i.e., a pure vestibular stimulation).Methods: Sixteen subjects (5 female and 11 male, 43.2 ± 17.0 years old) with chronic vestibular dysfunction that was non-responsive to other types of medical treatment were recruited for the study (ClinicalTrials.gov Identifier: NCT01080430). Subjects had VOR asymmetry quantified by an abnormal directional preponderance (DP) with rotation test and no previous history of central vestibular problems or fluctuating peripheral vestibular disorders. They participated either in the short-term study (one session) or the long-term study (7 visits over 5 weeks). Rehabilitation consisted of five trapezoid unidirectional rotations (peak velocity of 320°/s) toward the weaker side. Care was taken to slowly stop the rotation in order to avoid stimulation in the opposite direction during deceleration. To study the short-term effect, VOR responses were measured before and 10, 40, and 70 min after a single unidirectional rotational rehabilitation session. For long-term effects, the VOR gain was measured before and 70min after rehabilitation in each session.Results: We observed a significant decrease in VOR asymmetry even 10 min after one rehabilitation session (short-term study). With consecutive rehabilitation sessions in the long-term study, DP further decreased to reach normal values during the first 2 sessions and only one subjects required further rehabilitation after week 4. This change in DP was due to an increase in responses during rotations toward the weaker side and a decrease in VOR responses during rotations in the other direction.Conclusion: Our results show that unidirectional rotation can reduce the VOR imbalance and asymmetry in patients with previously compensated vestibular dysfunction and could be used as an effective supervised method for vestibular rehabilitation even in patients with longstanding vestibular dysfunction.

Prediction of Balance Compensation After Vestibular Schwannoma Surgery

Background. Balance compensation after vestibular schwannoma (VS) surgery is under the influence of specific preoperative patient and tumor characteristics. Objective. To prospectively identify potential prognostic factors for balance recovery, we compared the respective influence of these preoperative characteristics on balance compensation after VS surgery. Methods. In 50 patients scheduled for VS surgical ablation, we measured postural control before surgery (BS), 8 (AS8) days after, and 90 (AS90) days after surgery. Based on factors found previously in the literature, we evaluated age, body mass index and preoperative physical activity (PA), tumor grade, vestibular status, and preference for visual cues to control balance as potential prognostic factors using stepwise multiple regression models. Results. An asymmetric vestibular function was the sole significant explanatory factor for impaired balance performance BS, whereas the preoperative PA alone significantly contributed to higher performance at AS8. An evaluation of patients’ balance recovery over time showed that PA and vestibular status were the 2 significant predictive factors for short-term postural compensation (BS to AS8), whereas none of these preoperative factors was significantly predictive for medium-term postoperative postural recovery (AS8 to AS90). Conclusions. We identified specific preoperative patient and vestibular function characteristics that may predict postoperative balance recovery after VS surgery. Better preoperative characterization of these factors in each patient could inform more personalized presurgical and postsurgical management, leading to a better, more rapid balance recovery, earlier return to normal daily activities and work, improved quality of life, and reduced medical and societal costs.

Vestibular asymmetry predicts falls among elderly patients with multi-sensory dizziness

Background: Dizziness is the most common symptom in elderly patients and has been identified as a risk factor for falls. Multisensory deficits is the second most common cause of dizziness among elderly, with visual, vestibular and proprioceptive reduced function. Asymmetric vestibular function is overrepresented in elderly persons with hip fractures and wrist fractures and can be accessed for screening. Vestibular disorders are probably unrecognized as a cause to dizziness in the elderly. Given this, it is possible that elderly patients with multisensory dizziness also have asymmetric vestibular function to a high degree, which might indicate a higher risk of falls.

Vestibular asymmetry predicts falls among elderly patients with multi- sensory dizziness

BackgroundDizziness is the most common symptom in elderly patients and has been identified as a risk factor for falls. While BPPV is the most common cause of dizziness among elderly, multisensory deficits is the second, with visual, vestibular and proprioceptive reduced function. Asymmetric vestibular function is overrepresented in elderly persons with hip fractures and wrist fractures and can be accessed for screening.The objective was to study if vestibular asymmetry, vibration sense, balances performance, postural sway in quiet stance and self-perceived handicap because of dizziness could predict falls among elderly, dizzy patients.MethodsIn this prospective study with one year observation period, 55 patients (41 women, 14 men), 65 to 90 years old (median 80, interquartile range 11) with multisensory dizziness were included.Vestibular function was screened with the headshake test and vibration sense was assessed using a tuning fork. Balance was assessed with four clinical measures and self-perceived dizziness handicap was assessed by the Dizziness Handicap Inventory. Postural sway was measured using a force plate.ResultsHeadshake test were pathologic in 24 patients, which substantially increased the risk of falls (OR 3.4). Thirteen of the 21 patients who had fallen (p = 0.03), and all 6 patients who sustained three falls or more (p = 0.04), had vestibular asymmetry. No other measure could predict the risk of falls (OR 0.55–1.71).ConclusionSigns of vestibular asymmetry among elderly with multisensory dizziness could predict falls. Hence, it seems important to address fall-prevention programs to such a group of patients. Simple bedside tests of vestibular asymmetry might be a possibility to screen for one risk factor for falls among elderly.

Where is straight ahead to a patient with unilateral vestibular loss?

The vestibular system is classically associated with postural control, oculomotor reflexes and self-motion perception. The patients with vestibular loss are primarily concerned with balance and gait problems including head and trunk tilt and walking trajectory deviation to the lesioned side. These long-lasting postural and locomotor biases are thought to originate from changes in spatial perception of self. Indeed, we show here that vestibular cues are necessary for an accurate representation of body orientation. Patients with right (RVN; n=11) or left vestibular neurotomy (LVN; 9) as a treatment for Menière’s disease were compared with 10 healthy controls. The subjective straight ahead (SSA) was investigated using a method disentangling lateral shift and tilt components of error. In the horizontal plane, subjects were required to align a rod with their body midline. In the frontal plane, they were asked to align the rod with the midline of head or trunk. The analysis of SSA clearly showed distinct results according to the side of the lesion. The LVN patients had a contralesional lateral shift of SSA. In addition, they showed an ipsilesional tilt, more severe for the head than for the trunk. By contrast, in RVN patients, the representation of the body midline was fairly accurate in both the horizontal and frontal planes and did not differ from that of control subjects. The present study shows deviations in body orientation representation after unilateral vestibular loss. Deviations are observed in the horizontal as well as in the frontal planes. Interestingly, only patients with left vestibular loss were concerned with these changes in perception of self-orientation in space. These data support the hypothesis of an asymmetric vestibular function in healthy subjects and confirm the similarity of functional disorders in patients with vestibular deficits or spatial neglect. For the first time, this similarity is found at the level of body representation.

Use of a visual guide to improve the quality of VOR responses evoked by high-velocity rotational stimuli

High-velocity rotational stimuli have the potential to improve the diagnostic capabilities of clinical rotation testing by revealing nonlinear vestibulo-ocular reflex (VOR) responses that are indicative of asymmetric vestibular function. However, eye movements evoked by high-velocity rotations often are inconsistent over time and therefore do not yield reliable diagnostic measures. This study investigated whether use of a novel "visual guide" could improve the consistency and quality of VORs obtained during testing with pulse-step-sine (PSS) stimuli providing periodic high-velocity, horizontal-plane rotations with peak velocities up to 290 deg/s. The visual guide (narrow phosphorescent line spanning 180° field of view) was mounted horizontally on the rotation chair at the subject's eye level. Eight healthy human subjects were tested either in complete darkness while performing an alerting task, or while viewing the visual guide in an otherwise dark room. We found that the visual guide improved the quality of VOR responses as shown by an increased proportion of slow-phase velocity data segments retained for analysis, by a decreased variance of the processed eye velocity data, and by a reduction of outlying VOR response measures. We also found that the visual guide did not induce visual suppression because VOR gain measures were not diminished.

Observation of Vestibular Asymmetry in a Majority of Patients over 50 Years With Fall-Related Wrist Fractures

Previously, we have observed vestibular asymmetry in about one-third of healthy senior citizens and in about two-thirds of subjects with previous hip fractures and no other significant ailments. Wrist fractures are considered a harbinger of hip fractures. If vestibular asymmetry is correlated with falls and fractures among the elderly then it should also be reflected among subjects with wrist fractures. Sixty-six consecutive patients (mean age 67.8 years) who had sustained a fall-related wrist fracture during a 10-month period were included in the study. The frequency of head shake nystagmus among the patients was compared to that found among 49 healthy senior citizens (mean age 74.9 years). Nystagmus after head shaking, indicating asymmetric vestibular function, was found in 50 participants (76%) (p <0.001). Thirty-eight of these were graded with distinct or prominent nystagmus responses. Sixty percent of the subjects with horizontal nystagmus had a wrist fracture coinciding with the slow phase of nystagmus. Twenty-three subjects reported 30 previous fall-related fractures during the previous 10 years. Subjects with nystagmus after head shaking sustained 26 of these fractures. The frequency of signs of vestibular asymmetry was significantly higher (p <0.001) among the subjects than among healthy senior citizens. These findings suggest that an asymmetric vestibular function could be an epidemiologically important contributory factor to falls and wrist fractures among the elderly population.

Changes in Postural Control in Healthy Elderly Subjects are Related to Vibration Sensation, Vision and Vestibular Asymmetry

The aim of this study was to analyze the composition of sway in adults and "healthy" elderly people and to evaluate the influence of vibration sensation and asymmetric vestibular function on the sway pattern. Ten adults with a mean age of 37.5 years and 40 healthy senior citizens with a mean age of 74.6 years living independently in the community were studied. Vibration-induced body sway was measured on a force platform. The sway was analyzed and separated into its high and low frequency components above and below 0.1 Hz, respectively. Additionally the elderly subjects were observed for the occurrence of spontaneous gaze and head shake-induced nystagmus using infrared charge-coupled device cameras and the vibration perception in the lower limbs was tested with a tuning fork. Vibration perception was the major determinant for postural control in the elderly subjects. Postural control among the elderly subjects with intact vibration perception in their lower limbs was very similar to that of the adults. The elderly subjects with impaired vibration sensation had increased high frequency sway compared to adults and the elderly subjects with intact sensation. Regardless of the strong influence of vibration sensation on postural control, asymmetric vestibular function might also be a contributing factor to postural instability in the elderly. Age per se had little effect on the outcome of the tests except that the elderly subjects had diminished ability to use visual cues to reduce postural sway. We concluded that sensory status in the lower limbs is of utmost importance for postural control in the elderly. Rehabilitation programs for senior citizens should therefore include exercises to preserve recognition of body motion by the lower limbs. Exercises to facilitate vestibular compensation could be useful for elderly people with vestibular dysfunction.

Asymmetric optokinetic after-nystagmus induced by active or passive sustained head rotations.

Asymmetric vestibular function affects optokinetic after-nystagmus (OKAN) in man, but little is known about the involvement of cervical proprioception in the visual-vestibular interaction reflected as OKAN. We studied the effect of asymmetric cervical proprioception induced by active maximal, or passive 70 degrees sustained horizontal head rotations on OKAN in 16 healthy subjects. We evoked optokinetic nystagmus (OKN) by means of a whole-field optokinetic drum rotated at a velocity of 90 degrees/s for 60 s. Following left- and right-beating OKN, we recorded OKAN in complete darkness for 60 s by DC electro-oculography. Both passively and actively sustained head rotations significantly reduced the intensity of OKAN beating in the direction opposite to the head rotation, while OKAN beating in the direction of the head rotation remained unchanged. This resulted in significant asymmetry between OKAN beating in the direction of the head rotation vs. that in the opposite direction. The findings show that in normal subjects neck proprioception converges with visual and vestibular signals and affects subcortical OKN. Asymmetric neck proprioception from neck disorders may be hypothesized to induce dizziness or vertigo in situations where OKN is evoked.

Asymmetric Optokinetic Afterresponse in Patients with Vestibular Neuritis

The symmetry of primary and secondary optokinetic afternystagmus (OKAN I and OKAN II, respectively) was studied in 14 patients with vestibular neuritis, as well as in 50 normals. The patients were examined at onset of symptoms and at follow-up 3 and 12 months later. At onset, OKAN was found mainly to reflect the spontaneous nystagmus. Although the spontaneous nystagmus disappeared in all patients within 3 months, both OKAN I and OKAN II was asymmetric at the 3- and 12-month check-ups. OKAN beating toward the lesioned ear was weaker than the OKAN beating toward the healthy ear. Thus, the asymmetric vestibular function was reflected not only in the OKAN I, but also by an asymmetry in OKAN II. Between the 3- and 12-month check-ups, asymmetry in OKAN declined, even among those patients who showed no improvement in caloric response during that time. The decreasing asymmetry in OKAN with time after lesion was, however, related to the disappearance of a positional nystagmus. Hence, the results may be interpreted as suggesting OKAN not only to be affected by vestibular side-difference, but also to be modified by the process responsible for vestibular compensation following a peripheral vestibular lesion.

Diagnosis of Unilateral Otolith Hypofunction

Asymmetric vestibular function is the basis of vertigo. Whereas caloric tests can identify unilateral peripheral loss or impairment of horizontal semicircular canal function reasonably accurately, there is as yet no single accepted test of unilateral otolith hypofunction. In some advanced vestibular laboratories around the world, new and perhaps diagnostically useful tests of otolith function are being devised. The physiologic basis and the present clinical applications of these tests are reviewed.