Observations on normal and degenerating human otoconia

Otolithic functions in patients with residual dizziness after successful repositioning manoeuvres for unilateral posterior canal BPPV

OBJECTIVE

To evaluate otolithic functions in patients with residual dizziness after successful canalith repositioning procedures (CRPs) for unilateral posterior canal benign paroxysmal positional vertigo (BPPV), and to investigate possible risk factors.

METHODS

This case-control observational study included healthy controls and patients with residual dizziness after improvement following CRP for BPPV. All participants were subjected to full history taking, otoscopy, audiological basic evaluation, Dix-Hallpike test to search for posterior canal BPPV, residual dizziness screening, and vestibular evoked myogenic potential (VEMP) testing. Between-group differences were assessed and possible factors associated with residual dizziness were identified by univariate analysis.

RESULTS

A total of 50 patients with residual dizziness (mean age, 56.53 ± 7.46 years [29 female: 21 male]) and 50 healthy controls (mean age, 58.13 ± 7.57 years [20 female: 30 male]) were included. A significant difference in VEMP latencies was found between the patient and control group (delayed in the patient group), with no significant between-group difference in amplitude in both ears. Aging, female sex, long duration of BPPV, number of CRPs, cervical VEMP and ocular VEMP abnormalities, and winter onset, were significantly associated with the risk of residual dizziness.

CONCLUSIONS

Residual dizziness is a frequent sequel of BPPV that may relate to otolithic dysfunction. VEMP changes were revealed in the form of delayed latencies.

Otoconial Degeneration After Transient Ischemia Induced by Four-Vessel Occlusion in Rats

BACKGROUND AND PURPOSE

Ischemia of the inner ear may damage the otoconia. However, no study has explored any changes in the configuration of otoconia after transient ischemia of the labyrinth.

METHODS

Nineteen 7-week-old Sprague-Dawley rats were randomly assigned to either the sham (n=5) or the experimental group (n=14). The rats in the experimental group were subjected to global ischemia for 20 minutes using a four-vessel occlusion model, and were sacrificed seven days after the procedure. The rats in the sham group were sacrificed without any procedure. The otolithic organs (utricle and saccule) were dissected out for scanning electron microscope.

RESULTS

The otolithic organs in the sham group showed their normal gross configuration with a dense clumping of otoconia with a normal hexagonal morphology and a smooth surface. The otolithic organs in the experimental group also maintained a grossly normal configuration, but each otoconia showed irregular surfaces with numerous cracks or furrows, especially in the periphery of the otoconial bed.

CONCLUSIONS

The current study showed that otoconial degeneration may occur even after transient ischemia of the labyrinth. This finding supports an association between cerebral ischemia and benign paroxysmal positional vertigo.

Cellular and Molecular Mechanisms of Vestibular Ageing

While age-related auditory deficits and cochlear alterations are well described, those affecting the vestibular sensory organs and more broadly the central vestibular pathways are much less documented. Although there is inter-individual heterogeneity in the phenomenon of vestibular ageing, common tissue alterations, such as losses of sensory hair cells or primary and secondary neurons during the ageing process, can be noted. In this review, we document the cellular and molecular processes that occur during ageing in the peripheral and central vestibular system and relate them to the impact of age-related vestibular deficits based on current knowledge.

Advances in otolith-related protein research

Otoliths are biological crystals formed by a layer of calcium carbonate crystal that adhere to the ciliary surface of the utricular and saccular receptors in the vestibule of all vertebrates inner ear, enabling the utricle and saccule to better perceive the changes in linear and gravitational acceleration. However, the molecular etiology of otolith related diseases is still unclear. In this review, we have summarized the recent findings and provided an overview of the proteins that play important roles in otolith formation and maintenance (Otoconin-90, Otolin-1, Otolith Matrix Protein-1, Cochlin, Otogelin, α-Tectorin, β-Tectorin, Otopetrin-1, and Otopetrin-2, PMCA2, etc.), providing new insight for the prevention and management of benign paroxysmal positional vertigo (BPPV) with basis for otolith-related proteins as potential biomarkers of vestibular disease.

Age-related changes to vestibular heave and pitch perception and associations with postural control

Falls are a common cause of injury in older adults (OAs), and age-related declines across the sensory systems are associated with increased falls risk. The vestibular system is particularly important for maintaining balance and supporting safe mobility, and aging has been associated with declines in vestibular end-organ functioning. However, few studies have examined potential age-related differences in vestibular perceptual sensitivities or their association with postural stability. Here we used an adaptive-staircase procedure to measure detection and discrimination thresholds in 19 healthy OAs and 18 healthy younger adults (YAs), by presenting participants with passive heave (linear up-and-down translations) and pitch (forward-backward tilt rotations) movements on a motion-platform in the dark. We also examined participants' postural stability under various standing-balance conditions. Associations among these postural measures and vestibular perceptual thresholds were further examined. Ultimately, OAs showed larger heave and pitch detection thresholds compared to YAs, and larger perceptual thresholds were associated with greater postural sway, but only in OAs. Overall, these results suggest that vestibular perceptual sensitivity declines with older age and that such declines are associated with poorer postural stability. Future studies could consider the potential applicability of these results in the development of screening tools for falls prevention in OAs.

Otoconia Structure After Short- and Long-Duration Exposure to Altered Gravity

Vertebrates use weight-lending otoconia in the inner ear otolith organs to enable detection of their translation during self or imposed movements and a change in their orientation with respect to gravity. In spaceflight, otoconia are near weightless. It has been hypothesized that otoconia undergo structural remodeling after exposure to weightlessness to restore normal sensation. A structural remodeling is reasoned to occur for hypergravity but in the opposite sense. We explored these hypotheses in several strains of mice within a Biospecimen Sharing Program in separate space- and ground-based projects. Mice were housed 90 days on the International Space Station, 13 days on two Shuttle Orbiter missions, or exposed to 90 days of hindlimb unloading or net 2.38 g via centrifugation. Corresponding flight habitat and standard cage vivarium controls were used. Utricular otoliths were visually analyzed using scanning electron microscopy and in selected samples before and after focused ion beam (FIB) milling. Results suggest a possible mass addition to the otoconia outer shell might occur after exposure to longer-duration spaceflight, but not short ones or hindlimb unloading. A destructive process is clearly seen after centrifugation: an ablation or thinning of the outer shell and cavitation of the inner core. This study provides a purely descriptive account of otoconia remodeling after exposures to altered gravity. The mechanism(s) underlying these processes must be identified and quantitatively validated to develop countermeasures to altered gravity levels during exploration missions.

Evaluation of retrootolithic function using galvanic vestibular-evoked myogenic potentials in patients with benign paroxysmal positional vertigo

PURPOSE

The purpose is to investigate possible vestibulopathy in patients with benign paroxysmal positional vertigo (BPPV), inner ear tests, including cervical and ocular vestibular-evoked myogenic potentials (cVEMPs and oVEMPs) via various stimulation modes, were adopted.

METHODS

Fifty BPPV patients were enrolled in this study. All patients underwent pure tone audiometry, cVEMPs, oVEMPs, and caloric tests. The recurrence status, abnormal rates of inner ear tests, and the characteristic parameters of VEMPs, such as wave latencies and amplitudes, were analyzed.

RESULTS

In affected ears, the abnormal rates of acoustic cVEMPs, vibratory oVEMPs, galvanic cVEMPs, and galvanic oVEMPs were 62%, 28%, 36%, and 14%, respectively. The abnormalities of acoustic cVEMPs were significantly larger than those of vibratory oVEMPs, and acoustic/vibratory VEMPs had significantly higher abnormal rates than the corresponding galvanic VEMPs.

CONCLUSION

BPPV patients may have both otolithic and neural dysfunctions. Otolithic organ damage occurs more frequently than retrootolithic neural degeneration, and the saccular macula might have a greater extent of damage than the utricular macula.

A Synchrotron and Micro-CT Study of the Human Endolymphatic Duct System: Is Meniere's Disease Caused by an Acute Endolymph Backflow?

Background: The etiology of Meniere's disease (MD) and endolymphatic hydrops believed to underlie its symptoms remain unknown. One reason may be the exceptional complexity of the human inner ear, its vulnerability, and surrounding hard bone. The vestibular organ contains an endolymphatic duct system (EDS) bridging the different fluid reservoirs. It may be essential for monitoring hydraulic equilibrium, and a dysregulation may result in distension of the fluid spaces or endolymphatic hydrops. Material and Methods: We studied the EDS using high-resolution synchrotron phase contrast non-invasive imaging (SR-PCI), and micro-computed tomography (micro-CT). Ten fresh human temporal bones underwent SR-PCI. One bone underwent micro-CT after fixation and staining with Lugol's iodine solution (I2KI) to increase tissue resolution. Data were processed using volume-rendering software to create 3D reconstructions allowing orthogonal sectioning, cropping, and tissue segmentation. Results: Combined imaging techniques with segmentation and tissue modeling demonstrated the 3D anatomy of the human saccule, utricle, endolymphatic duct, and sac together with connecting pathways. The utricular duct (UD) and utriculo-endolymphatic valve (UEV or Bast's valve) were demonstrated three-dimensionally for the first time. The reunion duct was displayed with micro-CT. It may serve as a safety valve to maintain cochlear endolymph homeostasis under certain conditions. Discussion: The thin reunion duct seems to play a minor role in the exchange of endolymph between the cochlea and vestibule under normal conditions. The saccule wall appears highly flexible, which may explain occult hydrops occasionally preceding symptoms in MD on magnetic resonance imaging (MRI). The design of the UEV and connecting ducts suggests that there is a reciprocal exchange of fluid among the utricle, semicircular canals, and the EDS. Based on the anatomic framework and previous experimental data, we speculate that precipitous vestibular symptoms in MD arise from a sudden increase in endolymph pressure caused by an uncontrolled endolymphatic sac secretion. A rapid rise in UD pressure, mediated along the fairly wide UEV, may underlie the acute vertigo attack, refuting the rupture/K+-intoxication theory.

Two Symptoms Strongly Suggest Benign Paroxysmal Positional Vertigo in a Dizzy Patient

Introduction: This prospective cohort study determined which questions in patient history are most likely to identify symptoms that are independently associated with a diagnosis of benign paroxysmal positional dizziness (BPPV) in patients presenting with dizziness, and to evaluate whether the patient's age and type of BPPV are of influence. Methods: We included adult patients with dizziness referred to our dizziness center, Apeldoorn, the Netherlands, from December 2018 to November 2019. All patients completed a questionnaire, underwent vestibular testing and received a diagnosis. Symptoms strongly suggesting BPPV were tested with multivariable analysis to determine their independent associations with BPPV. Subgroup analysis was performed for patient age, and the type of BPPV. Results: We included a total of 885 patients, 113 of whom (13%) were diagnosed with BPPV. The duration of dizziness spells <1 min (Q2) and dizziness provoked by rolling over in bed (Q4) were independently associated with the diagnosis BPPV. Q2 showed a sensitivity of 43%, and a specificity of 75%; Q4 scored 81% and 68%, respectively. Overall, the way patients perceived their dizziness (vertigo, light-headedness or instability) was not independently associated with the diagnosis BPPV. In younger patients, light-headedness and instability decreased the likelihood of BPPV compared to vertigo. Conclusion: The most reliable predictors for BPPV in patient history are a short duration of the dizziness spell and provocation of dizziness by rolling over in bed. Unlike younger patients, elderly patients with BPPV do not only perceive the dizziness as vertigo, but also as a feeling of instability.

The Price of Immune Responses and the Role of Vitamin D in the Inner Ear

OBJECTIVE

In this review the authors discuss evidence from the literature concerning vitamin D and temporal bone diseases (benign paroxysmal positional vertigo [BPPV], Menière's disease [MD], vestibular neuritis, idiopathic facial paralysis, idiopathic acute hearing loss). Common features shared by Menière's disease, glaucoma, and the possible influence by vitamin D are briefly discussed.

DATA SOURCES, STUDY SELECTION

Publications from 1970 until recent times have been reviewed according to a keyword search (see above) in PubMed.

CONCLUSIONS

MD, BPPV, vestibular neuritis, idiopathic facial paralysis, idiopathic acute hearing loss may all have several etiological factors, but a common feature of the current theories is that an initial viral infection and a subsequent autoimmune/autoinflammatory reaction might be involved. Additionally, in some of these entities varying degrees of demyelination have been documented. Given the immunomodulatory effect of vitamin D, we postulate that it may play a role in suppressing an eventual postviral autoimmune reaction. This beneficial effect may be enhanced by the antioxidative activity of vitamin D and its potential in stabilizing endothelial cells. The association of vitamin D deficiency with demyelination has already been established in other entities such as multiple sclerosis and experimental autoimmune encephalitis. Mice without vitamin D receptor show degenerative features in inner ear ganglia, hair cells, as well as otoconia. The authors suggest further studies concerning the role of vitamin D deficiency in diseases of the temporal bone. Additionally, the possible presence and degree of demyelination in these entities will have to be elucidated more systematically in the future.

Investigation of inner ear anatomy in mouse using X-ray phase contrast tomography

A thorough understanding of inner ear anatomy is important for investigators. However, investigation of the mouse inner ear is difficult due to the limitations of imaging techniques. X-ray phase contrast tomography increases contrast 100-1,000 times compared with conventional X-ray imaging. This study aimed to investigate inner ear anatomy in a fresh post-mortem mouse using X-ray phase contrast tomography and to provide a comprehensive atlas of microstructures with less tissue deformation. All experiments were performed in accordance with our institution's guidelines on the care and use of laboratory animals. A fresh mouse cadaver was scanned immediately after sacrifice using an inline phase contrast tomography system. Slice images were reconstructed using a filtered back-projection (FBP) algorithm. Standardized axial and coronal planes were adjusted with a multi-planar reconstruction method. Some three-dimensional (3D) objects were reconstructed by surface rendering. The characteristic features of microstructures, including otoconia masses of the saccular and utricular maculae, superior and inferior macula cribrosae, single canal, modiolus, and osseous spiral lamina, were described in detail. Spatial positions and relationships of the vestibular structures were exhibited in 3D views. This study investigated mouse inner ear anatomy and provided a standardized presentation of microstructures. In particular, otoconia masses were visualized in their natural status without contrast for the first time. The comprehensive anatomy atlas presented in this study provides an excellent reference for morphology studies of the inner ear.

New advances regarding adaptation of the vestibulo-ocular reflex

This is a review summarizing the development of vestibulo-ocular reflex (VOR) adaptation behavior with relevance to rehabilitation over the last 10 years and examines VOR adaptation using head-on-body rotations, specifically the influence of training target contrast, position and velocity error signal, active vs. passive head rotations, and sinusoidal vs. head impulse rotations. This review discusses optimization of the single VOR adaptation training session, consolidation between repeated training sessions, and dynamic incremental VOR adaptation. Also considered are the effects of aging and the roles of the efferent vestibular system, cerebellum, and otoliths on angular VOR adaptation. Finally, this review examines VOR adaptation findings in studies using whole body rotations.

Otoconial loss or lack of otoconia - An overlooked or ignored diagnosis of balance deficits

HYPOTHESIS

Lack of otoconia or otoconial loss may be the major reason for increasing imbalance with age, posttraumatic dizziness and residual dizziness as well as other so far unexplained imbalance affecting probably millions of people.

BACKGROUND

It is written in every textbook that we need sensation of gravity for stable gait and stance, especially on two legs. Lack of otoconia is known to cause lifelong balance problems in animals. Loss of otoconia is happening in aging humans, like shown by increasing incidence of benign paroxysmal positional vertigo (BPPV) and in histological sections. While hundreds of papers have been published on BPPV, increasing imbalance with age and increasing falls, none has ever described the loss of otoconia as a major reason for this imbalance. Maybe this is due to the problems to proof this hypothesis in an individual patient. We will explain why otoconial loss may cause dizziness, postural and locomotor instability in patients with no other identifiable cause or in addition to other causes. Several reasons can cause otoconial loss and lead to the described symptoms. We will describe the symptoms and the tests which could in combination support the diagnosis.

CONCLUSION

Our hypothesis argues for the new diagnosis in many patients with so far undiagnosed or incorrectly or incompletely diagnosed dizziness or imbalance.

Seasonality and solar radiation variation level in benign paroxysmal positional vertigo

BACKGROUND

Several studies have shown that the incidence of benign paroxysmal positional vertigo (BPPV) presents seasonal variations and there is evidence that the variation in time is dependent on the patient's amount of vitamin D.

OBJECTIVES

This is a retrospective study to verify if there is a correlation between the incidence of BPPV and the level of solar radiation, essential for the synthesis of vitamin D in the skin.

MATERIAL AND METHODS

This study comprised 214 patients with BPPV seen from 2012 to 2017, in a city Latitude: -30.0277, Longitude: -51.2287 30° 1' 40″ South, 51° 13' 43″ West. The amounts of monthly solar radiation were analyzed in relation to the dates of their first consultations. Statistical tests were employed to verify the existence of a correlation between solar radiation and the incidence of the disease.

RESULTS

The statistical analysis revealed a significant difference between the incidence of BPPV and the amount of radiation during the month of the diagnosis of the disease. There was also a significant statistical correlation with the climatic variation.

CONCLUSION

More patients with benign paroxysmal positional vertigo (BPPV) are seen in consultation in the months with low solar radiation and in the autumn and winter seasons, in this geographic city.

Otopetrin-2 Immunolocalization in the Human Macula Utricle

BACKGROUND

In the present study, we investigated the localization of otopetrin-2-a member of the otopetrin family that encodes proton-selective ion channels-in the human macula utricle using immunohistochemistry.

METHODS

Macula utricle were acquired at surgery from patients who required transmastoid labyrinthectomy for intractable vertigo due to Meniere's disease (MD; n = 3) and/or vestibular drops attacks (VDA; n = 2) and from temporal bones (n = 2) acquired at autopsy from individuals with no balance disorders. Immunofluorescence staining with otopetrin-2 (rabbit affinity purified polyclonal antibody) and GFAP (mouse monoclonal antibody) to identify vestibular supporting cells was made in formalin fixed cryostat sections or whole microdissected utricle (for flat mount preparations). Secondary antibodies against rabbit and mouse were used for the identification of both proteins. Digital fluorescent images were obtained using a high-resolution laser confocal microscope.

RESULTS

Using cryostat sections and flat mount preparations otopetrin-2 immunofluorescence was seen as punctated signal throughout the supporting cells cytoplasm. GFAP immunofluorescence was present in the supporting cell cytoplasm. The distribution of otopetrin-2 was similar in the macula utricle obtained from MD, VDA, or autopsy normative patients.

CONCLUSIONS

Otopetrin-2 was localized in supporting cells in a similar fashion that otopetrin-1 previously reported in the mouse macula utricle. The differential expression of otopetrin-2 in the supporting cells of the human macula utricle suggest an important role in the vestibular sensory periphery homeostasis and otolith maintenance.

Generation of Vestibular Tissue-Like Organoids From Human Pluripotent Stem Cells Using the Rotary Cell Culture System

Hair cells are specialized mechanosensitive cells responsible for mediating balance and hearing within the inner ear. In mammals, hair cells are limited in number and do not regenerate. Human pluripotent stem cells (hPSCs) provide a valuable source for deriving human hair cells to study their development and design therapies to treat and/or prevent their degeneration. In this study we used a dynamic 3D Rotary Cell Culture System (RCCS) for deriving inner ear organoids from hPSCs. We show RCCS-derived organoids recapitulate stages of inner ear development and give rise to an enriched population of hair cells displaying vestibular-like morphological and physiological phenotypes, which resemble developing human fetal inner ear hair cells as well as the presence of accessory otoconia-like structures. These results show that hPSC-derived organoids can generate complex inner ear structural features and be a resource to study inner ear development.

The Vestibular System and Ageing

The world's population is ageing due to increased hygiene and improved medical care. Dizziness and imbalance frequently affect the elderly and is most common among individuals over the age of 60. In this age group approximately 30% of the population experience these debilitating symptoms at some point. They contribute to falls and frailty, which often result in hospitalization causing tremendous cost for the health care systems, and increased mortality. To make the matters worse balance disorders are often complex. Physicians face the difficulty of diagnosing the patient with the exact disorder especially since each disorder may manifest differently in each patient. In addition, several treatment options exist, however, with a low level of evidence. This chapter summarizes the underlying degenerative processes of the peripheral as well as the central vestibular system, diagnostic tools, the most common balance disorders in the elderly, and possible treatment options of these disorders.

Magnesium as an intrinsic component of human otoconia

OBJECTIVES

To investigate morphology changes of artificial otoconia (CGC) in the presence of magnesium during growth under in vitro conditions.

METHODS

Investigating human otoconia by environmental scanning electron microscope and determining their magnesium content by energy-dispersive X-ray microanalysis (EDX). Comparing structural and morphological data of human and artificial otoconia (CGC, Ca₁Mg₀) without and with magnesium substitution (Ca_1-xMg_x).

RESULTS

EDX- and X-ray data reveals that the inorganic component in human otoconia consists of calcite containing a minor amount of magnesium substitution (Ca_1-xMg_x). CGC containing magnesium (length 397.0 ± 146.4 µm, diameter 325.6 ± 100.1 µm) are slimmer and significantly smaller (p < .01) than pure CGC (length 548.6 ± 160 µm, diameter 373.0 ± 110.4 µm) and reveal a significant influence on the final morphology. The length/diameter ratio is significantly higher by incorporation of magnesium into CGC (1.84 ± 0.25 µm versus 1.48 ± 0.11 µm in pure CGC, p < .01), which brings the overall shape to a close relationship with human otoconia (1.98 ± 0.08 µm).

CONCLUSIONS

Magnesium is an intrinsic component of human otoconia by partial substitution of calcium in the calcite crystal structure (Ca_1-xMg_x) and affects the development of the shape of artificial otoconia (calcite gelatin composites, CGC).

Vitamin D supplementation may improve symptoms in Meniere's disease

In the last 4 years the authors observed a trend that correcting vitamin D deficiency in newly diagnosed cases of Meniere's disease decreased the necessity of the ablative therapy with intratympanic gentamicin. According to their hypothesis, vitamin D supplementation may indeed have a beneficial effect in Meniere's disease if the symptoms are caused by a local postviral autoimmune reaction. Vitamin D has a strong immunomodulatory role, one of which is the regulation of the expression of pro-inflammatory mediators. The authors suggest further epidemiological studies to decide if there is a connection between vitamin D deficiency and Meniere's disease.

Mechanism Underlying the Effects of Estrogen Deficiency on Otoconia

Otoconia-related vertigo and balance deficits, particularly benign paroxysmal positional vertigo (BPPV), are common. Our recent studies in humans show that, while BPPV prevalence greatly increases with age in both genders, peri-menopausal women are especially susceptible. In the present study, we show that bilateral ovariectomized (OVX) mice have significant balance behavioral deficits, and that estrogen deficiency compromises otoconia maintenance and anchoring by reducing the expression of otoconial component and anchoring proteins. There is ectopic debris formation in the ampulla under estrogen deficiency due to aberrant matrix protein expression. Furthermore, phytoestrogen is effective in rescuing the otoconia abnormalities. By comparing the expression levels of known estrogen receptor (Esr) subtypes, and by examining the otoconia phenotypes of null mice for selected receptors, we postulate that Esr2 may be critical in mediating the effects of estrogen in otoconia maintenance.

[The importance of vestibular evoked myogenic potentials for the assessment of the otolith function in the patients presenting with benign paroxysmal positional vertigo]

The objective of the present study was to evaluate the otolith function in the patients presenting with idiopathic benign paroxysmal positional vertigo (pBPPV) attributable to the occlusion of the posterior semicircular canal (PSCC) of the inner ear with the use of vestibular evoked myogenic potentials (VEMP). Cervical (cVEMP) and ocular VEMP (oVEMP) were measured in 34 patients with idiopathic pBPPV before and 7 days after the treatment by means of reposition maneuvers. The results of the repeated Dix-Hallpike test performed 7 days after the repositioning maneuver were negative in 27 patients and positive in 7 patients. There was no statistically significant difference in the amplitude of cervical VEMP between the healthy and affected ears either before or after the repositioning treatment. The measurement of oVEMP revealed a reduction of the response amplitude on the affected side. The average values of the plnl on the healthy side were 12.84±1.09 and those on the affected side 4.62±0.69 (p<0,05). The successful repositioning treatment resulted in a significant increase of the oVEMP amplitude on the affected side (p<0,05). In the patients presenting with the persistent symptoms of pBPPV, the repositioning maneuvers did not cause an appreciable increase in the amplitude of oVEMP on the affected side (p<0.05). The results of the present study give evidence that pBPPV of the posterior semicircular canal is associated with the impairment of the function of the receptor structures of the utriculus and the preserved function of the succulus as suggested by the reduction of the oVEMP amplitude and clinically significant asymmetry of ocular VEMP on the affected side with intact cervical VEMP on both sides. The successful treatment of pBPPV of PSCC with the use of the liberatory maneuver results in the increase of the oVEMP amplitude on the affected side increases while the response asymmetry between both sides significantly decreases which indicates the repair of the utriculus otolith function.

Decrease of Horizontal Canal Vestibulo-Oculomotor Reflex Gain in the Elderly with Dysequilibrium without Lifetime Vertigo

BACKGROUND/AIMS

Unsteadiness in the elderly is a frequent complaint and a strong predictor of falls and psychological distress. Although there is a general consensus that it is a multifactorial condition, recent studies have focused on the role of aging of the vestibular system as a possible cofactor. The aim of our work was to assess horizontal canal function in the elderly.

METHODS

We evaluated the gain of horizontal vestibulo-ocular reflex (VOR) with a video head impulse test on a sample of 58 subjects aged >70 years without lifetime episodes of vertigo and correlated the value with different clinical conditions (hypertension, diabetes, prior cardiovascular and vascular disorders of the central nervous system, and falls).

RESULTS

The mean value of the gain was 0.86 ± 0.12, and people aged between 70 and 80 years presented higher values (0.90 ± 0.1) compared to those >80 years (0.81 ± 0.13; p = 0.025). Previous vascular disorders of the central nervous system were a predictor of decreased VOR gain (p = 0.0003). A nonparametric analysis demonstrated that sex, age, and VOR gain (p ˂ 0.0001) were predictive of falls.

CONCLUSIONS

Our data support the hypothesis of a decrease of VOR gain in the elderly. The decrease of canal function may therefore play a role in the risk of falls in the elderly.

Biochemical markers of bone turnover in benign paroxysmal positional vertigo

Objective

Several studies have suggested a possible relationship between recurrent benign paroxysmal positional vertigo (BPPV) and altered calcium homeostasis in the endolymph of the inner ear. The present study aimed to evaluate the association between Ca²⁺ and vitamin D status and BPPV occurrence as well as the status of bone biochemical markers in osteoporotic patients who were diagnosed with idiopathic BPPV.

Methods

The study included total 132 patients who were referred to our clinic between August 2008 and October 2013. Based on the bone mineral density (BMD) results, the subjects were divided into three groups: normal BMD (n = 34), osteopenia (n = 40) and osteoporosis (n = 58). The biochemical markers of bone turnover including serum Carboxy-terminal telopeptide of type I collagen (s-CTX), osteocalcin, alkaline phosphatase (ALP) and urinary free deoxypyridinoline (u-DPD), were analyzed, along with the serum Ca²⁺ and vitamin D levels.

Results

The mean serum calcium, phosphate and creatinine clearance levels were within the standard laboratory reference range. The incidence of vitamin D deficiency was 11.8% (4/34) in the normal BMD group, 15% (6/40) in the osteopenia group and 43.1% (25/58) in the osteoporosis group. There was a positive correlation between the 25(OH)D and BMD results in the patients with BPPV. Among the bone turnover markers, the osteocalcin and u-DPD levels were significantly elevated in the osteoporotic patients with BPPV. Multiple logistic regression analyses showed that osteoporosis and vitamin D deficiency were associated with BPPV.

Conclusion

Our findings suggest that the prevalence of BPPV in osteoporotic patients is associated with vitamin D deficiency and high bone turnover rates at systemic level, which could disturb local Ca²⁺ homeostasis in the inner ear.

Age-Related Vestibular Loss: Current Understanding and Future Research Directions

The vestibular system sub-serves a number of reflex and perceptual functions, comprising the peripheral apparatus, the vestibular nerve, the brainstem and cerebellar processing circuits, the thalamic relays, and the vestibular cerebral cortical network. This system provides signals of self-motion, important for gaze and postural control, and signals of traveled distance, for spatial orientation, especially in the dark. Current evidence suggests that certain aspects of this multi-faceted system may deteriorate with age and sometimes with severe consequences, such as falls. Often the deterioration in vestibular functioning relates to how the signal is processed by brain circuits rather than an impairment in the sensory transduction process. We review current data concerning age-related changes in the vestibular system, and how this may be important for clinicians dealing with balance disorders.

Spatiotemporal differences in otoconial gene expression

Otoconia are minute biocrystals composed of glycoproteins, proteoglycans, and CaCO₃ , and are indispensable for sensory processing in the utricle and saccule. Otoconia abnormalities and degeneration can cause or facilitate crystal dislocation to the ampulla, leading to vertigo and imbalance in humans. In order to better understand the molecular mechanism controlling otoconia formation and maintenance, we have examined the spatial and temporal expression differences of otoconial genes in the mouse inner ear at developmental, mature and aging stages using whole transcriptome sequencing (RNA-Seq) and quantitative RT-PCR. We show that the expression levels of most otoconial genes are much higher in the utricle and saccule compared with other inner ear tissues before postnatal stages in C57Bl/6J mice, and the expression of a few of these genes is restricted to the embryonic utricle and saccule. After the early postnatal stages, expression of all otoconial genes in the utricle and saccule is drastically reduced, while a few genes gain expression dominance in the aging ampulla, indicating a potential for ectopic debris formation in the latter tissue at old ages. The data suggest that the expression of otoconial genes is tightly regulated spatially and temporally during developmental stages and can become unregulated at aging stages. Birth Defects Research (Part A) 106:613-625, 2016. © 2016 Wiley Periodicals, Inc.

Otoconia and otolithic membrane fragments within the posterior semicircular canal in benign paroxysmal positional vertigo

OBJECTIVES/HYPOTHESIS

Benign paroxysmal positional vertigo (BPPV) is the most common vestibular disorder with an incidence between 10.7 and 17.3 per 100,000 persons per year. The mechanism for BPPV has been postulated to involve displaced otoconia resulting in canalithiasis. Although particulate matter has been observed in the endolymph of affected patients undergoing posterior canal occlusion surgery, an otoconial origin for the disease is still questioned.

STUDY DESIGN

In this study, particulate matter was extracted from the posterior semicircular canal of two patients and examined with scanning electron microscopy.

METHODS

The samples were obtained from two patients intraoperatively during posterior semicircular canal occlusion. The particles were fixed, stored in ethanol, and chemically dehydrated. The samples were sputter coated and viewed under a scanning electron microscope. Digital images were obtained.

RESULTS

Intact and degenerating otoconia with and without linking filaments were found attached to amorphous particulate matter. Many otoconia appeared to be partially embedded in a gel matrix, presumably that which encases and anchors the otoconia within the otolith membrane, whereas others stood alone with no attached filaments and matrix. The otoconia measured roughly 2 to 8 μm in length and displayed a uniform outer shape with a cylindrical bulbous body and a 3 + 3 rhombohedral plane at each end.

CONCLUSIONS

These findings suggest that the source of the particulate matter in the semicircular canals of patients with BPPV is broken off fragments of the utricular otolithic membrane with attached and detached otoconia.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:709-714, 2017.

[Otoconia : Current aspects of research]

Otoconia are calcite-based nanocomposites containing >90 % calcite and <10 % organic material. The mean size is approximately 10 µm. The external structure of all otoconia in the utricle and saccule is similar, with a cylindrical bulbous body with a slightly hexagonal contour. The internal structure consists of a composite with varying volume thickness, dense branching structures (branches) and less dense surrounding areas (bellies). Intact otoconia can be clearly identified only by scanning electron microscopy. In the case of morphological changes (e.g. due to "degeneration") the origin of even very small particles of otoconia can be assigned using physical and chemical analytical methods. The inorganic component of otoconia (calcite) is extremely sensitive to chemical influences, which leads to morphological alterations. A "degeneration" of otoconia can be objectively accomplished in vitro by alterations in pH, electrolyte imbalance and by the influence of complex formation. These three main processes then lead to irreversible morphological alterations. Artificial (biomimetic) otoconia serve as a suitable model system for detailed investigation of growth and degenerative processes.

Molecular aging of the mammalian vestibular system

Dizziness and imbalance frequently affect the elderly and contribute to falls and frailty. In many geriatric patients, clinical testing uncovers a dysfunction of the vestibular system, but no specific etiology can be identified. Neuropathological studies have demonstrated age-related degeneration of peripheral and central vestibular neurons, but the molecular mechanisms are poorly understood. In contrast, recent studies into age-related hearing loss strongly implicate mitochondrial dysfunction, oxidative stress and apoptotic cell death of cochlear hair cells. While some data suggest that analogous biological pathomechanisms may underlie vestibular dysfunction, actual proof is missing. In this review, we summarize the available data on the molecular causes of vestibular dysfunction.

Otoconia: Mimicking a calcite-based functional material of the human body. From basic research to medical aspects

Otoconia (calcite-based biominerals) are part of the sensory system in the inner ear of vertebrates, acting as gravity receptors responding to linear accelerations. Biomimetic otoconia are grown by double-diffusion into gelatine-gel matrices, and represent the first example of successful imitation of a biomineral, not only in outer shape but also in composite structure and hierarchical inner architecture. Biomimetic and biogenic (human) otoconia are investigated by X-ray methods, chemical analytics, ESEM, and TEM. Shape development (morphogenesis) as well as (partial) dissolution of the calcite component of the composite underline the hierarchical inner architecture built of more dense rhombohedral branches (with plane end-faces) and a rounded, more porous belly area. Atomistic simulations are performed in order to get insight into very first nucleation steps. Based on the detailed observations made up to now, first assumptions for the function of otoconia are developed, including the questions of density distribution within the volume of the specimen, the surrounding endolymph, as well as anchoring and interconnections of otoconia. A final point concerns the degeneration of otoconia which is caused by complexing agents and/or changes in ion concentrations (and pH) of the endolymph.

Age-related decline in functional connectivity of the vestibular cortical network

In the elderly, major complaints include dizziness and an increasing number of falls, possibly related to an altered processing of vestibular sensory input. In this study, we therefore investigate age-related changes induced by processing of vestibular sensory stimulation. While previous functional imaging studies of healthy aging have investigated brain function during task performance or at rest, we used galvanic vestibular stimulation during functional MRI in a task-free sensory stimulation paradigm to study the effect of healthy aging on central vestibular processing, which might only become apparent during stimulation processing. Since aging may affect signatures of brain function beyond the BOLD-signal amplitude-such as functional connectivity or temporal signal variability--we employed independent component analysis and partial least squares analysis of temporal signal variability. We tested for age-associated changes unrelated to vestibular processing, using a motor paradigm, voxel-based morphometry and diffusion tensor imaging. This allows us to control for general age-related modifications, possibly originating from vascular, atrophic or structural connectivity changes. Age-correlated decreases of functional connectivity and increases of BOLD--signal variability were associated with multisensory vestibular networks. In contrast, no age-related functional connectivity changes were detected in somatosensory networks or during the motor paradigm. The functional connectivity decrease was not due to structural changes but to a decrease in response amplitude. In synopsis, our data suggest that both the age-dependent functional connectivity decrease and the variability increase may be due to deteriorating reciprocal cortico-cortical inhibition with age and related to multimodal vestibular integration of sensory inputs.

Effect of Otoconial Proteins Fetuin A, Osteopontin, and Otoconin 90 on the Nucleation and Growth of Calcite

We investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on calcite surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on crystal morphology. All three proteins were found to be potent inhibitors of calcite growth, although fetuin A promoted growth at concentrations below about 40 nM and only became an inhibitor at higher concentrations. We then used in situ optical microscopy to observe calcite nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the calcite nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous calcite nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution-substrate interfacial energy.

Mechanisms of otoconia and otolith development

BACKGROUND

Otoconia are bio-crystals that couple mechanic forces to the sensory hair cells in the utricle and saccule, a process essential for us to sense linear acceleration and gravity for the purpose of maintaining bodily balance. In fish, structurally similar bio-crystals called otoliths mediate both balance and hearing. Otoconia abnormalities are common and can cause vertigo and imbalance in humans. However, the molecular etiology of these illnesses is unknown, as investigators have only begun to identify genes important for otoconia formation in recent years.

RESULTS

To date, in-depth studies of selected mouse otoconial proteins have been performed, and about 75 zebrafish genes have been identified to be important for otolith development.

CONCLUSIONS

This review will summarize recent findings as well as compare otoconia and otolith development. It will provide an updated brief review of otoconial proteins along with an overview of the cells and cellular processes involved. While continued efforts are needed to thoroughly understand the molecular mechanisms underlying otoconia and otolith development, it is clear that the process involves a series of temporally and spatially specific events that are tightly coordinated by numerous proteins. Such knowledge will serve as the foundation to uncover the molecular causes of human otoconia-related disorders.

Mechanisms of otoconia and otolith development

BACKGROUND

Otoconia are bio-crystals that couple mechanic forces to the sensory hair cells in the utricle and saccule, a process essential for us to sense linear acceleration and gravity for the purpose of maintaining bodily balance. In fish, structurally similar bio-crystals called otoliths mediate both balance and hearing. Otoconia abnormalities are common and can cause vertigo and imbalance in humans. However, the molecular etiology of these illnesses is unknown, as investigators have only begun to identify genes important for otoconia formation in recent years.

RESULTS

To date, in-depth studies of selected mouse otoconial proteins have been performed, and about 75 zebrafish genes have been identified to be important for otolith development.

CONCLUSIONS

This review will summarize recent findings as well as compare otoconia and otolith development. It will provide an updated brief review of otoconial proteins along with an overview of the cells and cellular processes involved. While continued efforts are needed to thoroughly understand the molecular mechanisms underlying otoconia and otolith development, it is clear that the process involves a series of temporally and spatially specific events that are tightly coordinated by numerous proteins. Such knowledge will serve as the foundation to uncover the molecular causes of human otoconia-related disorders.

Menopause and benign paroxysmal positional vertigo

OBJECTIVE

This study was designed to examine the age and sex distribution and the effects of menopause in a large cohort of participants diagnosed with benign paroxysmal positional vertigo (BPPV).

METHODS

We analyzed 1,377 BPPV patients and surveyed 935 women from this group-all diagnosed at the Boys Town National Research Hospital in the last decade.

RESULTS

A detailed age and sex distribution analysis of BPPV onset showed that aging had a profound impact on BPPV occurrence in both sexes, and that perimenopausal women were especially susceptible to BPPV (3.2:1 female-to-male ratio). The latter is a novel finding and was confirmed by a direct survey of female BPPV patients (168 participated). In addition, there was a pronounced female preponderance (6.8:1 female-to-male ratio) in BPPV in the teenage group despite its low prevalence in this age group.

CONCLUSIONS

Data suggest that hormonal fluctuations (especially during menopause) may increase the tendency to develop BPPV.

Principles of calcite dissolution in human and artificial otoconia

Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (calcite gelatin nanocomposits) and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.

Effects of age on the tuning of the cVEMP and oVEMP

OBJECTIVES

The purpose of the present investigation was to define for young, middle-aged, and older adults the optimal frequency (cies) to record both the cervical vestibular-evoked myogenic potential (cVEMP) and the ocular vestibular-evoked myogenic potential (oVEMP). Further, this study aimed to describe age-related changes in the tuning of these two vestibular-evoked myogenic potentials.

DESIGN

This was a prospective study. Participants were 39 healthy adults (mean age 46.3 ± 15.7 years; range = 22 to 78 years; 15 men) equally divided into 3 age groups of 13 participants each: young adult (18 to 39 years), middle age (40 to 59 years), and old adult (≥60 years). cVEMPs and oVEMPs were recorded using air-conduction tone bursts at stimulus frequencies of 125, 250, 500, 750, 1000, 1500, and 2000 Hz presented at 127 dB pSPL.

RESULTS

There was a significant main effect of age group and frequency on the amplitude of both the cVEMP and the oVEMP. Amplitudes were largest for the Young adult group for the cVEMP and for the young adult and Middle age group for the oVEMP. The largest average peak-to-peak amplitude occurred in response to a 750 Hz tone burst for both responses. No significant differences in mean amplitude of the cVEMP or oVEMP were observed for 500, 750, or 1000 Hz stimuli. There was a significant interaction of age group and frequency for the cVEMP, suggesting a loss of tuning for the old adult group. Compared with the young adult group, the tuning of the cVEMP and oVEMP for the older adjults appeared to shift to a higher frequency.

CONCLUSION

There is no sharp tuning in the saccule and utricle. Instead, there is a range of best frequencies that may be used to evoke the cVEMP and oVEMP responses. The results of the present investigation also demonstrate that the optimal stimulus frequency to elicit a VEMP may change with age. Accordingly, 500 Hz may not be the ideal frequency to elicit VEMPs for all age groups. For this reason, in cases where the VEMP response is absent at 500 Hz it is recommended that attempts be made to record the VEMP for tone-burst frequencies of 750 or 1000 Hz.

An Analysis of Vestibular Evoked Myogenic Potentials in Patients With Benign Paroxysmal Positional Vertigo

Objective:

Vestibular evoked myogenic potentials (VEMPs) selectively test the vestibular end-organ. The aim of this study was to analyze how the site of the diseased canal, type of particulate deposition, duration of symptoms, severity of nystagmus, recurrence, and age affect the VEMP in patients with benign paroxysmal positional vertigo (BPPV).

Methods:

One hundred two patients were enrolled in the study between 2009 and 2012. There were 36 men and 66 women with ages ranging from 16 to 71 years (mean age, 42.28 ± 11.29 years). Patients with BPPV were tested with roll-on and head-hanging maneuvers under video-electronystagmography monitoring and with air conduction cervical VEMP testing. Patients were grouped for duration, severity, recurrence, age, site of canal involvement, and so on, and the results were compared in each subgroup. Kruskal–Wallis and Mann–Whitney U tests were used for the comparative analysis.

Results:

Twenty-four patients (23.5%) had a gross VEMP abnormality (absence of VEMP in 6 and greater than 25% depression of the amplitude in 18). Abnormality of VEMPs was not correlated with factors including age, severity of nystagmus, number of maneuvers applied, and the site of canal involvement ( P < .05). However, persistence or recurrence of symptoms has an effect on VEMP results ( P = .016).

Conclusion:

Vestibular evoked myogenic potential is a useful tool to study the otolithic function in patients with BPPV and should be included in the test battery.

In vitro calcite crystal morphology is modulated by otoconial proteins otolin-1 and otoconin-90

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia.

Gentamicin-induced structural damage of human and artificial (biomimetic) otoconia

CONCLUSIONS

Gentamicin causes irreversible structural damage of human and artificial otoconia by progressive dissolution of calcite. The inner architecture of otoconia is strongly affected by degradation scenarios during gentamicin exposure. Artificial otoconia can be used as a model system mimicking the chemical attacks for detailed investigations.

OBJECTIVES

To investigate the chemical interactions of gentamicin with natural calcite and human and artificial otoconia under in vivo conditions.

METHODS

Pure calcite crystals and artificial and human otoconia were exposed to gentamicin injection solutions at various concentrations. Morphological changes were observed in time steps by the use of environmental scanning electron microscopy (ESEM).

RESULTS

Dissolution of pure calcite crystals results in the formation of well oriented nanoshoots indicating an irreversible chemical reaction with gentamicin. Human and artificial otoconia reveal irreversible structural changes of their surface areas as well as of their inner structure, resulting in characteristic changes at different gentamicin concentrations. Minor changes are first observed by surface alterations and dissolution of calcite in the belly region. Major changes result in further reduction of the belly area reaching the center of symmetry. Finally, a complete dissolution of the branches takes place. Artificial otoconia provide detailed insight into surface alterations.

Neuroimaging to detect cortical projection of vestibular response to caloric stimulation in young and older adults using functional near-infrared spectroscopy (fNIRS)

Functional near-infrared spectroscopy (fNIRS) is a non-invasive and portable neuroimaging technique. The method uses non-ionizing laser light in the range of red to near-infrared to detect changes in cerebral blood oxygenation. In this study, we used fNIRS to investigate cortical hemodynamic changes in the temporo-parietal and frontal regions during caloric vestibular stimulation. Caloric stimulation has previously been investigated using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), which serves as a validation of the fNIRS imaging modality toward the measurement of vestibular related brain regions. To date, only a single study has used fNIRS during caloric irrigations, which observed blood volume changes in the temporal-parietal area in healthy younger subjects. In this current study, fNIRS was used to measure cortical vestibular activation in 10 right-handed younger subjects (5 male and 5 female, age 25+/-6 years) and 10 right-handed older subjects (6 male and 4 female, age 74+/-5 years). We investigated both warm (44 °C) and cool (30 °C) unilateral caloric vestibular stimulation. Consistent with previous reports, we found that warm (44 °C) caloric irrigation caused a bilateral activation. In addition, we found that cool (30 °C) caloric irrigation caused contralateral activation of the temporo-parietal area. This study is the first to investigate age effects of the caloric stimulation on brain activity. We found that the older subjects had stronger bilateral effects than the younger subjects. Our results confirm previous fMRI and PET studies that showed cortical activation during caloric vestibular irrigation is dependent on side of irrigation, and temperature of irrigation. Furthermore, our results demonstrate that fNIRS is a viable technique in measuring cortical effects during vestibular tasks.

Association between hearing loss and saccular dysfunction in older individuals

OBJECTIVE

1) Describe the association between hearing loss and dysfunction of each of the 5 vestibular end-organs--the horizontal, superior, and posterior semicircular canals; saccule; and utricle--in older individuals. 2) Evaluate whether hearing loss and vestibular end-organ deficits share any risk factors.

STUDY DESIGN

Cross-sectional study.

SETTING

Academic medical center.

PATIENTS

Fifty-one individuals age 70 years or older.

INTERVENTIONS

Audiometry, head-thrust dynamic visual acuity (htDVA), sound-evoked cervical vestibular-evoked myogenic potential (cVEMP), and tap-evoked ocular VEMP (oVEMP).

MAIN OUTCOME MEASURES

Audiometric pure-tone averages (PTA), htDVA LogMAR scores as a measure of semicircular canal function in each canal plane, and cVEMP and oVEMP amplitudes as a measure of saccular and utricular function, respectively.

RESULTS

We observed a significant correlation between hearing loss at high frequencies and reduced cVEMP amplitudes (or reduced saccular function; r = -0.37, p < 0.0001) in subjects age 70 years or older. In contrast, hearing loss was not associated with oVEMP amplitudes (or utricular function), or htDVA LogMAR scores (or semicircular canal function) in any of the canal planes. Age and noise exposure were significantly associated with measures of both cochlear and saccular dysfunction.

CONCLUSION

The concomitant decline in the cochlear and saccular function associated with aging may reflect their common embryologic origin in the pars inferior of the labyrinth. Noise exposure seems to be related to both saccular and cochlear dysfunction. These findings suggest a potential benefit of screening individuals with presbycusis-particularly those with significant noise exposure history-for saccular dysfunction, which may contribute to fall risk in the elderly.

Immunogold TEM of otoconin 90 and otolin - relevance to mineralization of otoconia, and pathogenesis of benign positional vertigo

Implementation of the deep-etch technique enabled unprecedented definition of substructural elements of otoconia, including the fibrillar meshwork of the inner core with its globular attachments. Subsequently the effects of the principal soluble otoconial protein, otoconin 90, upon calcite crystal growth in vitro were determined, including an increased rate of nucleation, inhibition of growth kinetics and significant morphologic changes. The logical next step, ultrastructural localization of otoconin 90, by means of immunogold TEM in young mature mice, demonstrated a high density of gold particles in the inner core in spite of a relatively low level of mineralization. Here gold particles are typically arranged in oval patterns implying that otoconin 90 is attached to a scaffold consisting of the hexagonal fibrillar meshwork, characteristic of otolin. The level of mineralization is much higher in the outer cortex where mineralized fiber bundles are arranged parallel to the surface. Following decalcification, gold particles, as well as matrix fibrils, presumed to consist of a linear structural phenotype of otolin, are aligned in identical direction, suggesting that they serve as scaffold to guide mineralization mediated by otoconin 90. In the faceted tips, the level of mineralization is highest, even though the density of gold particles is relatively low, conceivably due to the displacement by the dense mineral phase. TEM shows that individual crystallites assemble into iso-oriented columns. Columns are arranged in parallel lamellae which convert into mineralized blocks for hierarchical assembly into the complex otoconial mosaic. Another set of experiments based on immunogold TEM in young mice demonstrates that the fibrils interconnecting otoconia consist of the short chain collagen otolin. By two years of age the superficial layer of mouse otoconia (corresponding to mid-life human) has become demineralized resulting in weakening or loss of anchoring of the fibrils interconnecting otoconia. Consequently, otoconia detached from each other may be released into the endolymphatic space by minor mechanical disturbances. In humans, benign positional vertigo (BPV) is believed to result from translocation of otoconia from the endolymphatic space into the semi-circular canals rendering their receptors susceptible to stimulation by gravity causing severe attacks of vertigo. The combinations of these observations in humans, together with the presented animal experiments, provide a tentative pathogenetic basis of the early stage of BPV.

Aging effect on galvanic vestibular-evoked myogenic potentials

OBJECTIVE

This study compared the characteristic parameters of vestibular-evoked myogenic potentials (VEMPs) via galvanic vestibular stimulation (GVS) in healthy subjects of various ages to measure the effect of aging on GVS-VEMPs.

STUDY DESIGN

Prospective study.

SETTING

University hospital.

SUBJECTS AND METHODS

Fifty-two healthy subjects were divided into five groups by age. Each group consisted of 10 subjects in one decade (except 12 subjects in the group of 60 to 69 years). All subjects underwent VEMP testing via GVS with an intensity of 5 mA for 1 ms.

RESULTS

All 10 subjects (20 ears) in each group aged 20 to 29, 30 to 39, 40 to 49, and 50 to 59 years exhibited clear GVS-VEMPs, whereas 20 (83%) of 24 ears in the group aged 60 to 69 years had clear GVS-VEMPs, exhibiting nonsignificant differences in terms of prevalence between the groups of subjects younger and older than 60 years. The mean p13 and n23 latencies and p13-n23 amplitude of the subjects in the groups aged 20 to 29, 30 to 39, 40 to 49, 50 to 59, and 60 to 69 years differed significantly among the five groups: the p13 and n23 latencies of the group aged older than 60 years was significantly longer than those of subjects younger than 60 years and their p13-n23 amplitude was lower.

CONCLUSION

The decline of the amplitude and prolongation of the latencies in GVS-VEMPs after the age of 60 may, at least in part, be caused by the decrease in the number of vestibular afferents and their caliber.