A New Perspective to Interpret How the Vestibular Efferent System Correlates the Complexity of Routine Balance Maintenance with Management of Emergency Fall Prevention Strategies.

Bipedalism is unique among mammals. Until modern times, a fall and resulting leg fracture could be fatal. Balance maintenance after a destabilizing event requires instantaneous decision making. The vestibular system plays an essential role in this process, initiating an emergency response. The afferent otolithic neural response is the first directionally oriented information to reach the cortex, and it can then be used to initiate an appropriate protective response. Some vestibular efferent axons feed directly into type I vestibular hair cells. This allows for rapid vestibular feedback via the striated organelle (STO), which has been largely ignored in most texts. We propose that this structure is essential in emergency fall prevention, and also that the system of sensory detection and resultant motor response works by having efferent movement information simultaneously transmitted to the maculae with the movement commands. This results in the otolithic membrane positioning itself precisely for the planned movement, and any error is due to an unexpected external cause. Error is fed back via the vestibular afferent system. The efferent system causes macular otolithic membrane movement through the STO, which occurs simultaneously with the initiating motor command. As a result, no vestibular afferent activity occurs unless an error must be dealt with.

Evolution of postural control assessment: From dynamic posturography to virtual reality.

During the early years of spaceflight it was documented that astronauts were impaired and incapacitated upon return to earth. Computerized Dynamic Posturography (CDP) was devised to investigate and quantify this deficit, and eventually progressed into a clinical assessment tool. The current sprouting of virtual reality (VR) technologies has allowed for the development of an alternative approach that could be more informative. Many low-cost VR systems (including desktop gaming programs designed for rehabilitation) are now available. Continued improvements in this technology indicate a high probability that VR will become an integral component of posturography by replacing present mechanical CDP techniques. We researched the relevant literature to evaluate the strengths and weaknesses of CDP using the Equitest (Neurocom International; Clackamas USA), and the added benefits of incorporating VR to help clinicians assess the complex task of balance maintenance. VR is capable of manipulating task and environmental demands in order to assess functional postural behavior. VR is also a useful tool for clinical testing of postural disorders resulting from sensory mismatch. Although posturography is still a useful clinical tool, VR provides an inherent conflict between the visual and vestibular senses and can elevate the effectiveness of CDP for both assessment and intervention. We conclude that, when initially developed, CDP was innovative and ahead of its time. However, with the advent of VR, we have a chance to modernize CDP and enhance its value as a clinical instrument.

Vestibular Function Correlates with Radiologic Findings in a Gymnast with 22q11.2DS.

BACKGROUND The 22q11.2 deletion syndrome (22q11.2DS) is the most common identified microdeletion in humans. Anomalies of the vestibular system can occur with great frequency and are reported in the radiology literature. Fewer reports exist regarding vestibular function or its clinical features. CASE REPORT We present a case report of a competitive gymnast with 22q11.2DS who was noted to be having specific issues related to balance under conditions of competition, specifically on the balance beam. Comprehensive balance assessment provided evidence of the absence of lateral semicircular canal function, correlating with computed tomography findings and her symptoms. Counselling and targeted training greatly improved her performance. CONCLUSIONS Comprehensive balance testing correlated with clinical and radiographic findings in a competitive gymnast with 22q11.2DS. Results demonstrated the functional aspect of this anomaly but also displayed the extent to which the complex interactions of all components of balance can work together to overcome balance issues under intense vestibular stress.

Computerized Dynamic Posturography does not detect measured CVEMP and OVEMP abnormalities.

BACKGROUND: Computerized Dynamic Posturography (CDP)was developed by the American space program to assess imbalance in astronauts, and eventually evolved into a clinical diagnostic tool. However it is not a specific measure of vestibular function. Vestibular Evoked Myogenic Potential testing (VEMPs) is a new clinical tool which is sensitive and specific for measuring otolithic pathology, especially in the atypical vestibular patient. RESEARCH QUESTION: As posturography measures ability to maintain balance, and VEMP testing measures the structures responsible for this, we wondered if CDP results would correlate with VEMP abnormalities in the clinical setting. METHODS: We analysed 180 patients sequentially referred to our unit for vestibular complaints. All patients had a full battery of vestibular assessments. We correlated VEMP results with CDP results to look for abnormality patterns and correlations. An occasional patient's only abnormality was on CDP RESULTS: There was a high rate of VEMP abnormalities seen, which correlates with the fact that our referral base consists of patients with chronic vestibular complaints. The rate of VEMP abnormalities was the same in patients with normal CDP and those with abnormal CDP. SIGNIFICANCE: Our results do not suggest that CDP is unnecessary, but we feel that they emphasize the idea that these tests are measuring two different aspects of balance control. In some patients, all assessments are abnormal, but in some patients only one assessment is abnormal, suggesting that these modalities measure different things and are all important in the diagnostic armamentarium. Hopefully in the near future, the use of virtual reality will reduce the cost of CDP to the point where it can be made widely accessible to patients and clinicians.

Cost-effective evaluation of the vestibular patient.

PURPOSE OF REVIEW: There is in existence a large array of sophisticated equipment to assess patients with complaints of dizziness and imbalance. Many vestibular tests are expensive to administer. In an era of evidence-based medicine and economic austerity, the appropriate utilization of such tests is of paramount importance. This review examines the clinical value together with costs involved in performing the various components of the vestibular assessment battery. RECENT FINDINGS: Vestibular testing is expensive. To date, publications to support the use of specialist tests for the confident diagnosis of specific vestibular pathologies are severely lacking. In fact, over the last 12 months, the literature illustrates a reduction in the enthusiasm for some tests that were popularized over recent decades. SUMMARY: Tests of vestibular function are expensive and their ability to diagnose specific vestibular pathologies is lacking. However, there are some tests that, when used in specific circumstances, may be very helpful in the diagnosis and management of patients with these complaints.

Clinical romberg testing does not detect vestibular disease.

OBJECTIVE: To evaluate the effectiveness of tandem Romberg and tandem walking testing at detecting vestibular disease and to increase the difficulty of these standard screening assessments in an attempt to try and make them more effective in the clinical office setting. STUDY DESIGN AND SETTING: A prospective study in a tertiary and quaternary care neuro-otology clinic comparing performance on tandem Romberg and tandem walking between patients with vestibular disease and controls matched for age and sex. RESULTS: Making the tandem Romberg test and tandem walking tests more difficult for patients was not helpful because it also made the tests more difficult to perform for controls with no symptoms of vestibular disease. When comparing a young and an old cohort, there was a significant difference in performance. CONCLUSION: Our techniques of sharpening and sensitizing tandem Romberg and tandem walking tests were not useful at delineating vestibular disease, and age itself may be a confound that mimics the effects of balance system disease. SIGNIFICANCE: The tandem Romberg and tandem walking tests, despite being in widespread clinical use as office screening tests, may not be effective at determining the presence of newly developed vestibular disease.

Evaluation of the effects of ethanol on static and dynamic gait.

OBJECTIVE: We used two balance assessment devices, computerized dynamic posturography (CDP) and Swaystar transducers to detect subtle balance system deficits in nine subjects who had ingested minimal amounts of alcohol. DESIGN: Nine subjects were evaluated with both modalities before, and repetitively after, ingesting a small amount of alcohol. METHODS: We measured condition 5 (sway referenced platform; eyes closed) on CDP and tandem walking with eyes closed while wearing Swaystar to see if either test could detect a balance deficit. MAIN OUTCOME MEASURES: We measured total sway amplitude with eyes closed in pitch and roll planes during tandem walking with Swaystar, and static balance scores of CDP sensory organization testing condition 5 before and after alcohol ingestion at 20 min intervals. RESULTS: Although there was no detectable deficit measurable by CDP, eight of our nine subjects showed increased dynamic sway as measured by Swaystar, after alcohol ingestion. Total sway was significantly greater (p=.05) after alcohol ingestion. CONCLUSION: It is important to assess dynamic, rather than static, equilibrium as it may have potential in detecting very subtle balance deficits.

Increasing the usefulness of tandem walking evaluation.

OBJECTIVE: Tandem walking testing is a "standard" clinical technique for assessing balance and gait, but it is not a standardized test. We wished to develop a protocol by which we could measure sway during tandem walking at a patient's preferred cadence and at an altered cadence, which might be more challenging. DESIGN: Fifteen patients with vestibular complaints were evaluated with standard tandem walking testing while wearing the Swaystar belt-mounted accelerometer and were also assessed in the same way with tandem walking at two altered cadences. METHODS: We measured tandem walking sway amplitude and sway velocity with eyes open in both pitch and roll planes at a patient's preferred cadence, at 75% of their preferred cadence, and at 125% of their preferred cadence. MAIN OUTCOME MEASURES: We measured total sway amplitude and sway velocity in pitch and roll planes during tandem walking with eyes open while wearing Swaystar to see if there was any increase in sway at nonpreferred cadences. RESULTS: There was no correlation between preferred cadence and the age of the patient. However, there was a significant increase in both sway amplitude and sway velocity at both of the nonpreferred cadences. CONCLUSION: Disruption of a patient's preferred cadence may present an unnatural task, and this challenge to a patient's innate gait may help detect subtle vestibular disease.

Visual vestibular mismatch in patients treated with intratympanic gentamicin for Meniere's disease.

OBJECTIVE: To support the hypothesis that the symptom complex known as visual vestibular mismatch (VVM) can be induced by peripheral vestibular disease. DESIGN: Retrospective chart review; prospective questionnaire. SETTING: A tertiary/quaternary care hospital clinic. METHODS: The charts of 28 patients who were treated for Meniere's disease were studied. Their responses to a pretreatment VVM questionnaire were scored and compared with their answers in a telephone follow-up to the same questions posttreatment. These questionnaires were compared with those filled in by 100 control patients without ear disease. MAIN OUTCOME MEASURES: Patients' responses to a VVM-specific questionnaire. RESULTS: Seventeen of 28 patients had VVM. Gentamicin therapy increased the number of positive answers. There was no correlation between the development of VVM complaints, caloric scores, and posturography performance. No control patients had symptoms of VVM. CONCLUSION: We conclude that the development of VVM indicates the onset or worsening of vestibular disease as it can be induced or exacerbated by gentamicin therapy. As there is no correlation between VVM and caloric scores, we suggest that otolithic damage may be responsible for this symptom set developing.

Motion sickness and vestibular hypersensitivity.

OBJECTIVE: Motion sickness is poorly understood, although it has been recognized for years as debilitating. Vestibular function is required for motion sickness to occur, but motion sickness can also be brought on without body motion. The aim of this study was to see if there was a correlation between caloric response and motion sickness susceptibility. DESIGN: One experiment was a prospective study carried out on 200 patients. A second prospective study was carried out on 121 patients. SETTING: Patients referred to our tertiary/quaternary care dizziness clinic. METHODS: In experiment 1, caloric scores in patients were correlated with symptoms of motion sickness as established by responses to a simple question. In experiment 2, caloric scores were correlated with symptomatic responses to caloric testing itself. MAIN OUTCOME MEASURES: Caloric responses of the best ear were measured according to standardized caloric evaluation methods. RESULTS: There was no correlation between motion sickness and caloric scores. There was a significant difference in caloric scores between patients made symptomatic by calorics and those who were not. CONCLUSIONS: The autonomic response seen in some patients is not triggered by a specific level of semicircular canal response (as measured by caloric testing). We hypothesize that (similar to space motion sickness) the trigger is a signal differential that arises between semicircular canals and otoliths and that some patients are unable to suppress this response. These patients often suffer motion sickness on a long-term basis.