Mechanical Causes of Fluctuant Hearing Loss

Correlating atmospheric pressure and temperature with Meniere attack

OBJECTIVE

This paper correlated the Meniere attack with meteorological parameters i.e. atmospheric pressure, temperature, relative humidity and rainfall, to investigate which parameters that trigger the Meniere attack.

METHODS

During the past three years, totally 283 (2015), 351 (2016) and 319 (2017) patients with Meniere's disease (MD) were encountered at a clinic of the university hospital, accounting for 13%, 17% and 16% incidence in relation to overall annual neurotological cases, respectively. The onset of Meniere attack was then correlated with meteorological parameters.

RESULTS

The mean seasonal incidence of Meniere attack in relation to overall seasonal neurotological cases in 2015-2017 were 14.8 ± 2.8% (spring), 17.5 ± 2.2% (summer), 16.0 ± 1.8 % (autumn) and 12.8 ± 2.0% (winter), indicating that summer season had a higher incidence of Meniere attacks than winter season. Onset of Meniere attacks correlated significantly with the atmospheric pressure (r = -0.4484, p = 0.0061) and temperature (r = 0.4736, p = 0.0035), and the atmospheric pressure was highly negatively correlated with the temperature (r = -0.9421, p < 0.0001). In contrast, no correlation was identified between the onset of Meniere attacks and relative humidity or rainfall. The atmospheric pressure in the same month with typhoon compared with that without typhoon revealed a median reduction of 13.1 hectopascal.

CONCLUSION

Atmospheric pressure and temperature are correlated with the onset of Meniere attack. Summer season has a higher incidence of Meniere attack than winter season, likely because low atmospheric pressure in summer may aggravate endolymphatic hydrops, especially when accompanied by typhoons in the northwest Pacific region.

Magnetic resonance imaging: Role on diagnosing all types of endolymphatic hydrops

BACKGROUND/PURPOSE

This study utilized the recently advanced technique in MR imaging to establish its role on diagnosing all types of endolymphatic hydrops (EH).

METHODS

Twenty-two patients (26 ears) with clinical EH were admitted due to acute hearing loss and/or vertiginous attack. Each patient underwent an inner ear test battery comprising audiometry, cervical and ocular vestibular-evoked myogenic potential tests, and caloric test, followed by MR imaging for confirmation.

RESULTS

Of the 22 clinical EH patients, 12 patients were referred to primary EH (Meniere's disease), 8 patients were secondary EH (including delayed EH in 5), and 2 patients were EH of embryopathic origin. MR imaging of 26 affected ears demonstrated EH in the cochlea only for 14 ears, in the utricle and saccule only for 1 ear, and in all three endorgans for 3 ears, accounting for a sensitivity of 69% (18/26). The 8 affected ears showing negative MR images were EH patients with hearing recovery 1, just after vertiginous attack 3, and chronic low-tone hearing loss 4. In contrast, 3 out of 18 unaffected ears demonstrated asymptomatic EH in the cochlea, representing a specificity of 83% (15/18).

CONCLUSION

The sensitivity and specificity of MR imaging for confirming all types of EH were 69% and 83%, respectively. Although diagnostic criteria can identify primary and delayed EH, MR imaging may provide a supplementary tool for diagnosing secondary, embryopathic, or asymptomatic EH, if patients are not with hearing recovery, chronic low-tone hearing loss, or just after vertiginous attack.

Saccular otoconia as a cause of Ménière's disease: hypothesis based on two theories

BACKGROUND

The cause of Ménière's disease remains enigmatic after 156 years. Schuknecht's rupture and potassium intoxication theory of attacks was based on histological studies.

OBJECTIVES

This paper aimed to: present the most contemporary evidence indicating that ruptures do not usually occur, and discuss the possibility that detached saccular otoconia are the main cause of Ménière's disease; and to establish an unequivocal definition of the age of Ménière's disease onset.

METHOD

The paper reviews the electrophysiological basis of the Gibson-Arenberg drainage theory used to explain vertigo attacks. The current, limited knowledge of the likely fate of detached saccular otoconia is discussed.

RESULTS

Electrophysiological studies during attacks do not support endolymph ruptures, but rather endolymph flowing in one direction and then in the opposite direction. Age of onset for Ménière's disease parallels that for benign paroxysmal positional vertigo.

CONCLUSION

The similarity of age of onset spectrum for Ménière's disease and benign paroxysmal positional vertigo raises the possibility that the two conditions have the same fundamental cause.

Changes in Vestibular Evoked Myogenic Potentials after Meniere Attacks

Objectives:

The aim of this study was to apply videonystagmography (VNG) and vestibular evoked myogenic potential (VEMP) tests to patients with Meniere attacks, to explore the mechanics of where saccular disorders may affect the semicircular canals.

Methods:

From January 2001 to December 2003, 12 consecutive patients with unilateral definite Meniere's disease with vertiginous attacks underwent VNG for recording spontaneous nystagmus, as well as VEMP tests.

Results:

At the very beginning of the Meniere attack, the spontaneous nystagmus beat toward the lesion side in 5 patients (42%) and toward the healthy side in 7 patients (58%). Twenty-four hours later, only 6 patients (50%) showed spontaneous nystagmus beating toward the healthy side. Nevertheless, spontaneous nystagmus subsided in all patients within 48 hours. The VEMP test was performed within 24 hours of a Meniere attack; the VEMPs were normal in 4 patients and abnormal in 8 patients (67%). After 48 hours, 4 patients with initially abnormal VEMPs had resolution and return to normal VEMPs, and the other 4 patients still had absent VEMPs.

Conclusions:

Most patients (67%) with Meniere attacks revealed abnormal VEMPs, indicating that the saccule participates in a Meniere attack. This is an important idea that stimulates consideration of the mechanism of Meniere attacks.

Atmospheric Pressure and Onset of Episodes of Menière's Disease - A Repeated Measures Study

Background

External changes of air pressure are transmitted to the middle and inner ear and may be used therapeutically in Menière’s disease, one of the most common vertigo disorders. We analyzed the possible relationship of atmospheric pressure and other meteorological parameters with the onset of MD vertigo episodes in order to determine whether atmospheric pressure changes play a role in the occurrence of MD episodes.

Methods

Patients of a tertiary outpatient dizziness clinic diagnosed with MD were asked to keep a daily vertigo diary to document MD episodes (2004–2009). Local air pressure, absolute temperature and dew point temperature were acquired on an hourly basis. Change in meteorological parameters was conceptualized as the maximum difference in a 24 hour time frame preceding each day. Effects were estimated using additive mixed models with a random participant effect. We included lagged air parameters, age, sex, weekday and season in the model.

Results

A total of 56 persons (59% female) with mean age 54 years were included. Mean follow-up time was 267 days. Persons experienced on average 10.3 episodes during the observation period (median 8). Age and change in air pressure were significantly associated with vertigo onset risk (Odds Ratio = 0.979 and 1.010). We could not show an effect of sex, weekday, season, air temperature, and dew point temperature.

Conclusions

Change in air pressure was significantly associated with onset of MD episodes, suggesting a potential triggering mechanism in the inner ear. MD patients may possibly use air pressure changes as an early warning system for vertigo attacks in the future.

Analysis of auditory and vestibular function in patients with unilateral Meniere's disease

CONCLUSION

The percentage of the unilateral weakness of the caloric response also reflects the clinical progress of Meniere's disease (MD), including clinical hearing loss.

OBJECTIVE

To evaluate the relationship between hearing status and vestibular function in patients with MD.

METHODS

Seventy-nine patients with unilateral definite MD underwent bithermal air caloric testing, vestibular evoked myogenic potential (VEMP) testing, and pure tone audiometry (PTA). The stages of the disease, clinical hearing level of the diseased ears, and dPTA (the difference in hearing level between ears in each patient) were compared with the percentage of the unilateral weakness of the caloric response and the interaural amplitude difference (IAD) ratio of the VEMP response.

RESULTS

Twenty ears (25.3%) revealed normal caloric responses and 59 ears (74.7%) showed reduced caloric responses. Testing revealed that the VEMPs were normal in 49 ears (62%), while 30 ears (38%) had abnormal VEMPs. The percentage of the unilateral weakness of the caloric response was positively correlated with the clinical hearing level of the diseased ears (p = 0.006) and the dPTA (p = 0.013).

Augmentation of ocular vestibular-evoked myogenic potentials via bone-conducted vibration stimuli in Ménière disease

OBJECTIVE

The asymmetry ratio of ocular vestibular-evoked myogenic potential (oVEMP) >40% is interpreted as augmented or reduced response depending on whether the nI-pI amplitude of the lesion ear is larger or smaller than that of the opposite ear, respectively. This study compared unilateral Ménière disease patients with augmented oVEMPs vs reduced oVEMPs to elucidate the mechanism of augmented oVEMP.

STUDY DESIGN

Case series with chart review.

SETTING

University hospital.

METHODS

Forty patients with unilateral definite Ménière disease were enrolled in this study, including 20 patients with augmented oVEMPs and another 20 patients with reduced oVEMPs in the hydropic side. All patients underwent audiometry, caloric test, and oVEMP and cervical VEMP (cVEMP) tests via bone-conducted vibration stimuli. Then, the oVEMP and cVEMP test results were compared with the stage of Ménière disease, respectively.

RESULTS

The augmented group had earlier nI and pI latencies and larger nI-pI amplitude of oVEMPs compared with the reduced group. Caloric test also revealed a significant difference in abnormal responses between the augmented and reduced groups. However, both groups did not differ significantly in the abnormal percentage of cVEMP test results. A significant trend to decline in the prevalence of augmented oVEMPs was noted from stages I to III-IV but not in that of abnormal cVEMPs.

CONCLUSION

The augmented oVEMPs have earlier latencies and larger amplitudes compared with the reduced oVEMPs, indicating that a relatively larger population of intact utricular afferents is activated during the early stage of Ménière disease.

Chronological changes in the eighth cranial nerve compound action potential (CAP) in experimental endolymphatic hydrops: the effects of altering the polarity of click sounds

CONCLUSION

Using a guinea pig model of experimental endolymphatic hydrops, click sounds of altered polarity showed different latencies and amplitudes in hydropic compared with normal cochleae. Latency changes appeared as early as 1 week after endolymphatic obstruction. This method can help diagnose endolymphatic hydrops.

OBJECTIVE

The goal of the study was to develop an objective electrophysiological diagnosis of endolymphatic hydrops.

MATERIALS AND METHODS

Endolymphatic hydrops were created surgically in guinea pigs. The latency and the amplitude of the eighth cranial nerve compound action potential (CAP) for click sounds of altered polarity were measured up to 8 weeks after the surgery.

RESULTS

At early stages after surgery, the latency for condensation clicks became longer, and at later stages the latencies for both condensation and rarefaction became longer. The discrepancy in the latencies for rarefaction and condensation click sounds (rarefaction minus condensation) became larger by the first week after surgery, but no further discrepancy occurred thereafter. Compared with latency changes, amplitude changes in the CAP were rapid and progressive following surgery, suggesting ongoing damage to hair cells.

Prognosis of low-tone sudden deafness - does it inevitably progress to Meniere's disease?

CONCLUSION

We conclude that not all low-tone sudden deafness (SD) patients suffered from endolymphatic hydrops even if they had vertigo attack at the onset and that electrocochleography (ECochG) was a useful prognostic tool.

OBJECTIVES

To investigate whether low-tone SD was a precursor of Meniere's disease and whether patients with low-tone SD suffered from endolymphatic hydrops.

PATIENTS AND METHODS

This was a retrospective case review in the university hospital. A total of 184 patients with low-tone SD were divided into two groups with single and recurrent episodes. The progress, follow-up audiograms, and ECochG results of the patients were reviewed and compared with those of patients with high-tone SD and Meniere's disease.

RESULTS

In all, 83 of 177 patients with low-tone SD unaccompanied by vertigo had recurrent hearing loss; 15 of the 83 developed vertiginous attacks. The remaining 94 patients had a single episode. Three of the seven patients with low-tone SD accompanied by vertigo had recurrent hearing loss; two of the three were subsequently confirmed to have Meniere's disease. The other four had a single episode. No difference in rate of progress from SD to Meniere's disease was observed among the low-tone and the high-tone SD groups. The average -SP/AP of each group with a single episode is smaller than that of other groups with recurrent episodes and Meniere's disease.

Vestibular evoked myogenic potentials: optimal stimulation and clinical application

By easily stimulating the ear with loud sound and recording on tonically contracted neck muscles, vestibular evoked myogenic potential (VEMP) test can reflect inner ear function other than the cochlea and semicircular canal. This expands the test battery for clinicians to explore saccular disease, adding a potential usefulness to the sacculo-collic reflex. The ideal stimulation mode for VEMPs is as follows: 95 dB tone bursts, frequency 500 Hz, stimulation repetition rate 5 Hz, rise/fall time 1 ms, plateau 2 ms, binaural stimulation with bilateral recordings. Animal model using guinea pigs has been established, which sets the stage for useful future studies investigating VEMPs in guinea pigs that would appear to resemble human VEMP responses. Clinically, VEMP test has been widely used in central and peripheral vestibular disorders.

Basilar membrane displacement related to endolymphatic sac volume

OBJECTIVE

To demonstrate that the amount of basilar membrane displacement toward the scala tympani and its attachment to the bony wall of the scala tympani (i.e., interscalar septum) in hydropic temporal bones is related to the intraosseous endolymphatic sac volume.

STUDY DESIGN

A retrospective analysis of temporal bones from individuals with the histopathologic diagnosis of "endolymphatic hydrops."

METHODS

Fifty-two temporal bones, from 38 patients, with the histopathologic findings of "endolymphatic hydrops" were analyzed microscopically. Data were obtained regarding the displacement of the basilar membrane, endolymphatic sac volume, hair cell loss, strial atrophy, ganglion cell loss, and last measured auditory thresholds. The relationships between these variables were examined statistically.

RESULTS

Nineteen of the 52 temporal bones (36.5%) with endolymphatic hydrops showed displacement of the basilar membrane toward the scala tympani in the apical and middle segments of the cochlea. A reduced volume of the endolymphatic sac was significantly related to increased severity of basilar membrane deformation (Rho = -.646; P < or = .001). Multiple regression analysis showed that severity of basilar membrane deformation was the single best predictor of low frequency thresholds while loss of hair cells was the best predictor of pure-tone average threshold.

CONCLUSIONS

The displacement of the basilar membrane in the apical and middle segments that may occur with endolymphatic hydrops, to the extent that it impinges on the interscalar septum, is related to a reduction in the intraosseous endolymphatic sac volume.

History of Meniere's disease and its clinical presentation

The term Meniere's disease is used to define either the classic triad of vestibular and cochlear symptoms and aural pressure from known or unknown causes or its clinical variants, vestibular and cochlear Meniere's disease. Some variants evolve after years into typical forms, whereas others do not. Some symptoms (positional vertigo) have been long underestimated in previous reports. The more we study our patients and correlate clinical findings and the natural history with pathologic studies on temporal bones and laboratory research, the more we will understand Meniere's disease and its causes. Some causes have already been identified as most probable. Extrinsic factors (inflammation, trauma, otosclerosis, autoimmunity, endocrine disorders, and such) interact with congenital (genetic) and developmental intrinsic factors (primary or secondary, acquired) into a multifactorial inheritance that is, to date, the best explanation for the basis of Meniere's disease. Endolymphatic hydrops is widely accepted as the pathologic substrate, but not all hydrops seems to be progressive or becomes clinically manifest. Endolymphatic hydrops is the result of a dysfunction in the mechanism of production/absorption of endolymph, which is mainly due to defective absorptive activity of the endolymphatic duct and sac. Hyperproduction of endolymph cannot be excluded in some cases. Ruptures of the labyrinthine membranes do not satisfactorily substantiate the multiform duration, recurrence, and repetitiveness of attacks of Meniere's disease, nor do they explain the entire complex of symptoms. It seems reasonable to explain symptoms of Meniere's disease on the basis of mechanical factors (as observed in temporal bone studies) associated with biologic and biochemical factors.

Relationship of vestibular aqueduct and inner ear pressure in Ménière's disease and the normal population

OBJECTIVE

Etiopathogenesis of Ménière's disease has not been resolved. The principal histopathologic finding in this disease is endolymphatic hydrops. The majority of radiologic and histopathologic studies demonstrated a narrow vestibular aqueduct in Ménière's disease. There is no study in the literature investigating the relationship between inner ear pressure and vestibular aqueduct dimensions. Static acoustic compliance is a noninvasive procedure that is thought to measure perilymphatic pressure at the footplate. An increase in mechanical fluid pressure in the inner ear is transmitted to the footplate of the stapes. This causes a reduction in the compliance at the drum. The aim of this study is to investigate the relationship between vestibular aqueduct dimensions and static acoustic compliance in Ménière's disease and the normal population.

STUDY DESIGN

Prospective study.

METHODS

Forty patients with Ménière's disease and 40 healthy individuals with no otolaryngologic disorders were the subjects of this study. Each group was further divided into two according to static compliance value (normal and low static compliance). In these four groups dimensions of vestibular aqueduct were determined radiologically by high-resolution computerized tomography and correlated with normal and low static acoustic compliance values (normal and high perilymphatic pressure).

RESULTS

The results demonstrated that vestibular aqueduct is narrower in patients with Ménière's disease than the normal population. However, there is no relationship between vestibular aqueduct dimensions and inner ear pressure obtained by static acoustic compliance measurements.

Meniere's disease and endolymphatic hydrops without Meniere's symptoms: temporal bone histopathology

We studied temporal bone histopathology in 21 ears with Meniere's disease and 24 ears with endolymphatic hydrops without Meniere's symptoms and compared the findings to those in 10 ears with presbycusis and 11 ears with normal hearing. Normal hearing ears showed less degeneration of cochlear structures than the other ears. In ears with endolymphatic hydrops without Meniere's symptoms, the degeneration of spiral ligament, hair cells, dendrites (peripheral processes) and apical spiral ganglion cells was more severe than in the other three groups. In ears with Meniere's disease and endolymphatic hydrops without Meniere's symptoms, the hair cells and dendrites were more affected than ganglion cells and there was no correlation between hair cell and ganglion cell degeneration. These findings suggest that a permanent threshold shift in late stage endolymphatic hydrops is not related to ganglion cell loss but rather to degeneration of sensory elements.

Electrocochleographic signal analysis: condensation and rarefaction click stimulation contributes to diagnosis in Menière's disorder

Thirty patients with Menière's disorder, 11 patients with cochlear hearing loss of other aetiologies and 10 normally-hearing subjects, were investigated using transtympanic electrocochleography (TT ECochG). Alternating polarity clicks, condensation and rarefaction clicks and long tone-bursts of 1 kHz were used for stimulation. The latencies of the AP responses to click stimulation were evaluated. It was found that the latency differences between the condensation and rarefaction click-evoked responses were significantly larger in patients with Menière's disorder as compared to normal subjects and to patients with other cochlear hearing losses. It was found that the sensitivity of TT ECochG, obtained by using measurements of SP-AP ratios and the SP amplitude at 1 kHz burst stimulation, increased from 83 per cent to 87 per cent by addition of the con-rar shift measurement. The specificity of TT ECochG obtained by this combination of variables was 100 per cent in our material. The results of the study indicate that the latency shift found in responses evoked by clicks of opposite polarities in TT ECochG, can be a useful parameter in the detection of suspected endolymphatic hydrops.

Derived-band auditory brain-stem response estimates of traveling wave velocity in humans: II. Subjects with noise-induced hearing loss and Meniére's disease

Estimates of cochlear traveling wave velocity (TWV) were computed from derived-band auditory brain-stem response (ABR) latencies in subjects with noise-induced hearing loss (NIHL) or Meniére's disease (MD). ABR wave V latencies were determined for each of six derived frequency bands (unmasked-8 kHz, 8-4 kHz, 4-2 kHz, 2-1 kHz, 1 kHz-500 Hz, and 500-250 Hz). Representative frequencies were assigned to the derived bands by estimating their energy midpoints, and cochlear positions corresponding to these frequencies were determined using Greenwood's (1961) place-frequency function for humans. An exponential function of the form I = A + BeCd was fitted to each subject's latency-by-distance data using a least-squares algorithm, and a TWV function was generated by taking the reciprocal of the derivative of the latency function with respect to distance [v = 1/(BCeCd)]. Expected values for subjects' TWV functions were compared to normative data from Donaldson and Ruth (1993) at five cochlear loci. NIHL subjects' TWV estimates fell within normal limits at all cochlear loci, and no relation between severity of high-frequency hearing loss and TWV could be discerned. MD subjects with good low-frequency hearing sensitivity generally yielded normal TWV estimates, whereas MD subjects with low-frequency hearing loss yielded either normal or elevated TWVs. MD subjects' data generally support the hypothesis that endolymphatic hydrops results in increased TWV or, alternatively, a basalward shift in the peak of the traveling wave, in cochleas with presumed normal basilar membrane elasticity.

Neurotologic findings in basilar migraine

Treatment of a patient with otologic symptoms and associated migraine-like headache presents the otolaryngologist with formidable problems. Although clinical practice and scientific publications recognize their frequent association, relationships have yet to be well defined. This study seeks to add order to disarray by delineating symptoms and signs of a clearly identified group of migraine patients. Fifty patients with well-defined basilar migraine underwent a thorough neurotologic examination, as well as comprehensive auditory and vestibular testing. Patients were selected from 5880 patients seen over a 2-year period and were prospectively entered into the study after detailed questionnaires and testing were completed for each patient. The most common symptoms found were dysequilibrium, phonophobia, and head pressure. The most common signs were positional nystagmus, low-frequency hearing loss, abnormal loudness discomfort level, and an abnormality on caloric examination. Advanced vestibular testing showed abnormal amplitude scaling, abnormal toes-down pertubation, and an abnormal sway (condition 6) on dynamic posturography. There was frequently an asymmetry on computerized rotation. The author concludes that the majority of patients have subtle findings on testing, but a few have severe peripheral injury due to the basilar migraine. Findings are consistent with the theory that basilar migraine is a central nervous system maladaptation syndrome which creates otoneurologic symptoms and, in a small percentage of cases, may injure the peripheral end-organ.

Effect of external auditory canal pressure upon the hearing threshold in patients with Menière's disease

Fluctuation of hearing at low frequencies is one of the most characteristic findings in Meniere's disease and seems to be a phenomenon closely related to changes of endolymphatic pressure and volume. In the present study, pressure was applied to the external auditory canal of patients with Meniere's disease, and the effect on the bone conduction threshold was examined at times of depressed and improved hearing. In more than half of these cases, it was found that the pressure effect was marked at the time of improved hearing acuity, but not at the time of depressed hearing. This effect was also confirmed in more objective experiments with guinea pigs. It is concluded that the fluctuation of hearing in Meniere's disease seems to be a phenomenon accompanying the endolymphatic pressure change in the scala media.

Analysis of the glycerin test for Menière's disease

The glycerin test has low sensitivity for Menière's disease using present published criteria. The purpose of this study is to compare the efficacy of standard empirical criteria with our theoretically based criteria. Subjects were 47 patients with Menière's disease and 45 patients with other causes of hearing loss and dizziness. Pure-tone thresholds and word-identification scores were determined before and 3 hours after administration of glycerin. The results were submitted to decision and multivariate discriminate analyses. The theoretically based criterion applied to pure-tone threshold testing alone was the most effective protocol for glycerin testing. Combining pure-tone thresholds and word-identification increased the false-positive rate without adequately increasing the true-positive rate, and provided no advantage over testing thresholds alone.

Hydrostatic pressure measurements of endolymph and perilymph in a guinea pig model of endolymphatic hydrops

The primary histologic correlate of Menière's disease is endolymphatic hydrops. From this, many investigators have postulated the existence of endolymphatic hypertension, although there have been no measurements published to substantiate this concept. Seventy guinea pigs, surgically treated with right endolymphatic duct obstruction, were later assessed by use of a micro-electrode technique that measured their endolabyrinthine hydrostatic pressures. For 21 of these animals, the pressures of both scala tympani (Pst) and scala media (Psm) of both ears of each animal were successfully measured. Similar measurements were made in a control group of 25 guinea pigs that had not undergone any previous surgery. For normal ears--as well as those with hydrops-pressure differences between perilymph and endolymph (Psm - Pst) varied around 0 +/- 2.0 mm Hg. When only the right (obstructed) ears were considered, there appeared to be a slight, relative pressure elevation (p less than 0.05) in scala media during the first 7 days after endolymphatic duct obstruction-and in those ears with EP, less than 70 mV. The magnitude of this pressure difference that can be attributed to the state of endolymphatic hydrops-and not to natural variability-is calculated (within 95% confidence limits) to be less than 0.5 mm Hg.

Air-bone gap in Menière's disease after exposure to overpressure

Equal loss in sensitivity for air and bone conduction and poor speech discrimination are considered characteristic of the hearing impairment in Menière's disease. Periodic pressure changes applied to the middle ear produced an air-bone gap in 16 out of 19 patients with advanced Menière's disease. The air-bone gap was associated with an improvement in speech discrimination scores. Subsequently, the air-conduction hearing loss decreased. The shapes of psychoacoustic tuning curves of patients with the air-bone gaps showed an improvement in frequency resolution. The curves remained elevated in threshold, however, which indicates an attenuation of the sound stimuli. The relative change in bone conduction sensitivity was interpreted as an early sign of improvement in the inner ear mechanics, caused by exposure to pressure changes.

Experimental studies on mechanism of the Menière's attack: investigation into vestibulo-cochlear response of the guinea pig induced by potassium ion

After introducing potassium ion through the round window into the perilymphatic space of 40 guinea pigs by means of iontophoresis, physiological and histochemical investigations were performed to determine the role of the high perilymphatic potassium concentration in the vertiginous attack of Ménière's disease. About 15 min after the iontophoretic procedure, electronystagmography revealed irritative nystagmus for the first 5 min and then paralytic nystagmus for the following 6 to 24 hr. Histochemical analysis of the vestibular sensory epithelia revealed the increased activity of succinic dehydrogenase and Na-K-ATPase during irritative nystagmus and the decreased activity during paralytic nystagmus. The Na-K-ATPase activity was dominant in the synaptic area between the hair cells and the nerve-endings of the vestibular sensory epithelia. There was some delay between the reversal of nystagmus-direction and the change of enzyme activity. This delay was thought to be produced by the central regulatory mechanism for the disturbed tonus-balance in the vestibular nucleus. On the other hand, electrocochleography revealed the decrease of the action potential without any initial irritative cochlear sign, and the enzyme activity of the cochlear sensory cells was decreased from the beginning.

Meniere's disease: a long-term follow-up study of hearing loss

Twenty patients suffering from Meniere's disease or Lermoyez syndrome were studied with respect to the time course of their hearing loss. Careful history-taking as well as repeated audiometry over long time spans (5-20 years) resulted in a longitudinal study of hearing loss at the standard audiometric frequencies. From these time series, correlation coefficients were computed between the changes in both ears at identical frequencies, and for changes in the same ear at different frequencies. Correlations between changes in hearing loss in both ears were more obvious in bilateral Meniere's disease than in unilateral disease. Correlations between changes in hearing loss at different frequencies were also more pronounced in Meniere's disease ears than in normal ears. If was found that recovery of hearing loss after an attack was nearly identical each time it occurred in the same ear, but differed between ears and patients. This deterministic finding in the otherwise random course of the hearing loss as a function of time may be important in deciding what mechanisms cause fluctuating hearing loss in Meniere's disease.

Otoadmittance changes following glycerol dehydration in Meniere's disease

Otoadmittance studies were undertaken in 76 patients with Meniere's disease and 8 control subjects undergoing glycerol dehydration. Baseline otoadmittance values were significantly higher in ears with fluctuant hydrops compared to the non-fluctuant ears (p less than 0.01), suggesting that there is a pathophysiological difference between these clinical Meniere's groups. Significant maximum conductance changes were seen in 53.4% of hydroptic ears, and were associated with subjective audiometric threshold shifts in 23.2%. Similar changes were not seen in the control ears. These findings provide further clinical evidence to support an underlying physical basis for the auditory symptoms of endolymphatic hydrops and the effects of glycerol dehydration on the inner ear. Objective otoadmittance changes appear to be a more sensitive indicator of reversible hydrops than conventional audiometry. Possible mechanisms to explain the somewhat paradoxical increase in the resistance to the flow of sound energy through the cochlea following reduction of the endolymphatic hydrops by glycerol dehydration are discussed.

Menière's disease and endolymphatic hydrops: clinical-histopathological correlations

The clinical-histopathological correlation between Menière's disease and endolymphatic hydrops was done to explain, as much as possible, causes of symptoms of Menière's disease. Twenty-three temporal bones with endolymphatic hydrops from 17 patients were reviewed and clinical and histopathological findings were correlated. Histopathological examination revealed frequent, severe deformities in the labyrinthine walls and permanent changes in Reissner's membranes. Evidence of rupture was difficult to assess. Of 21 ears of patients with the clinical diagnosis of Menière's disease, 93% had endolymphatic hydrops. A statistical correlation between increased area of the cochlear duct and hearing loss was found. Some correlation was also found between frequency of vertigo and results of electronystagmography with histopathological findings. Consequently, the mechanical effect of endolymphatic hydrops seems to have greater significance in the production of symptoms of Menière's disease than the biochemical effect of ruptures. In a review of ten unusual cases from this series of 17 patients, traumatic neuromas or remnants of vestibular structures were found after an incomplete labyrinthectomy. Histopathological findings of four patients who had undergone endolymphatic subarachnoid shunt surgery are described.