Measurement of endolymphatic pressure

Historical Therapies for Suspected Autonomic Dysregulation in Meniere's Disease

OBJECTIVE

This narrative review examines how speculative belief that the autonomic nervous system causes Meniere's Disease (MD) led otolaryngologists to adopt invasive surgical procedures and medical treatments still offered today.

DATA SOURCES

Google Scholar, PubMed.

REVIEW METHODS

A comprehensive literature review (1860-2022) was performed using the terms "Meniere AND (sympathetic OR sympathectomy OR vasomotor OR cervical ganglion)," returning 5360 items. All abstracts were briefly reviewed, relevant publications selected for further study, and key articles discussed by all authors. As it became clear that betahistine was related to the historical narrative, an additional search was performed using "Betahistine AND Meniere AND (vasomotor OR sympathetic OR sympathectomy OR cervical ganglion OR autonomic)," which yielded 336 results.

RESULTS

In the 19th and 20th centuries, growing knowledge of human anatomy led the scientific community to speculate that autonomic dysregulation caused many medical conditions. Excessive sympathetic mediated vasomotor changes were thought to cause hypertension, ischemia, and tissue damage. Clinicians applied the hypothesis to MD, assigning the sympathetic nervous system responsible for vertigo secondary to paroxysmal vasospasm and for hearing loss to poor cochlear nutrition. Despite limited animal experiments and isolated clinical observations, otolaryngologists performed sympathectomies, and, in the 1970s, replaced the procedure with betahistine as an alternative medical treatment.

CONCLUSION

Premature excitement about a plausible hypothesis led to unnecessary and unwarranted operations. Despite absent evidence of sympathetic overactivation in MD, surgeons eagerly adopted sympathectomies, and later betahistine. Rigorous evaluation of the validity of these treatment practices is needed.

LEVEL OF EVIDENCE

5 Laryngoscope, 134:535-542, 2024.

Impact of endolymphatic hydrops on DPOAE in subjects with normal to mild hearing loss

Objective

The increased endolymph volume affects a shift in the organ of Corti and basilar membrane in ears with endolymphatic hydrops (EH), which might affect distortion-product otoacoustic emissions (DPOAE) by altering the operating point of the outer hair cells. We investigated how changes in DPOAE are related to the distribution site of EH.

Study Design

Prospective study.

Methods

Among 403 patients with hearing or vestibular symptoms who underwent contrast-enhanced magnetic resonance imaging (MRI) for the diagnosis of EH and subsequent DPOAE testing, subjects whose hearing levels on pure tone audiometry were ≤35 dB at all frequencies were included in this study. In patients with EH on MRI, the presence and amplitude of DPOAE were evaluated between groups with hearing levels of ≤25 dB at all frequencies versus hearing levels of >25 dB at one or more frequencies.

Results

There were no differences in the distribution of EH between groups. The amplitude of DPOAE had no clear correlation with the presence of EH. However, in both groups, there was a significantly higher probability of the presence of a DPOAE response from 1001 to 6006 Hz in cases with EH in the cochlea.

Conclusion

Among patients whose hearing levels were ≤35 dB at all frequencies, better responses on DPOAE testing were found in subjects with EH in the cochlea. Alteration of DPOAEs in the early stages of hearing impairment could indicate morphological changes in the inner ear with altered basilar membrane compliance due to EH.

Level of Evidence

4.

The Role of Wideband Tympanometry in the Diagnosis of Meniere's Disease

Meniere's disease (MD) is a clinical syndrome characterized by spontaneous recurrent vertigo, usually accompanied by hearing loss, tinnitus, and aural fullness. The cause of MD remains unclear and is generally considered to be associated with endolymphatic hydrops. Studies showed that patients with MD could have eustachian tube dysfunction (ETD). ETD can disrupt the pressure balance between the middle and inner ear and impair the inner ear's function. In recent years, several studies have attempted to identify MD by using wideband tympanometry (WBT). However, there are limited studies in this area. There is no consensus on how to use WBT to diagnose Meniere's disease. Therefore, we endeavored to conduct a narrative review in this aspect based on the latest research findings. Reduction in resonance frequency and absorbance are characteristic of MD and can identify Meniere's disease. The use of an increase in the integrated area of absorbance as an indicator for identifying MD is controversial. WBT seems to be ineffective as a diagnostic tool during the acute episodes of Meniere's disease. Patients with MD may benefit from WBT. WBT has excellent potential for future use in Meniere's disease. However, further large sample sizes, multicenter studies are needed.

A possible mechanism of the formation of endolymphatic hydrops and its associated inner ear disorders

The pathology of Meniere's disease (MD) is well established to be endolymphatic hydrops. However, the mechanism underlying deafness and vertigo of MD or idiopathic endolymphatic hydrops is still unknown. In order to evaluate the pathogenesis of deafness and vertigo in MD, it seems to be rational to investigate the interrelationship between hydrops and inner ear disorders using animals with experimentally-induced endolymphatic hydrops. In spite of intense efforts by many researchers, the mechanism of vertiginous attack has been unexplained, because animals with experimental hydrops usually did not show vertiginous attack. Recently, there are two reports to succeed to evoke vertiginous attack in animals with experimental hydrops. In the present paper were first surveyed past proposals about underlying mechanism of the development of hydrops and inner ear disorders associated with hydrops, and were discussed the pathogenetic mechanism of vertiginous attack in hydrops. In conclusion, abrupt development of hydrops was thought to play a pivotal role in the onset of vertiginous seizure.

Evaluation of the Effects of Chronic Kidney Disease and Hemodialysis on the Inner Ear Using Multifrequency Tympanometry

OBJECTIVES

To evaluate the effects of chronic kidney disease (CKD) and hemodialysis (HD) on the inner ear using the G width (the width between the bimodal peaks of the conductance (G) tympanogram at 2,000 Hz), which reflects the inner ear pressure and/or the existence of endolymphatic hydrops.

MATERIALS AND METHODS

We selected five patients (10 ears) from the patients with CKD who were hospitalized for creation of arteriovenous fistula prior to initiation of HD (non-HD group), and we selected seven patients (14 ears) from the patients with CKD who were undergoing HD (the HD group). As a control group, we selected 80 healthy individuals (160 ears); these were mainly the medical staff of the hospital. We measured the G width of the control group and that of patients with CKD using multifrequency tympanometry.

RESULTS

The mean G widths of the HD (measured just before an HD session), non-HD, and control groups were 210.7, 128.4, and 97.0 daPa, respectively. The G width of the HD group was significantly greater than that of the control and non-HD groups (p<0.01 and p<0.01, respectively; Tukey-Kramer test after one-way analysis of variance). The non-HD group also had a greater G width than the control, but it was not significant (p=0.20; Tukey-Kramer). No significant changes were observed in the G widths of the HD group, just before and after a single HD session (p=0.423; paired t-test).

CONCLUSION

The greater G width observed in hemodialyzed CKD patients suggests either an increased inner ear pressure or the existence of endolymphatic hydrops in these patients, which is probably related to their otologic symptoms.

Otological symptoms and audiometric findings in patients with temporomandibular disorders: Costen's syndrome revisited

Objective:

Otological symptoms (otalgia, subjective hearing loss, blocked ear sensation, tinnitus and vertigo) associated with temporomandibular disorders are documented features of Costen's syndrome. However, the origin of these symptoms and the causes of hearing loss are unknown. This study aimed to characterise hearing loss in a large number of patients with temporomandibular disorders. The causes of these symptoms were explored in patients with otological symptoms and normal audiometric findings.

Methods:

A prospective case study and literature review were performed. The audiometric features of 104 temporomandibular disorder patients were compared with those of 110 control participants.

Results:

A large proportion of temporomandibular disorder patients had several otological symptoms. Twenty-five per cent of unilateral or bilateral temporomandibular disorder patients had either unilateral (ipsilateral) or bilateral hearing loss; respectively, which was usually mild (p = 0.001). Hearing loss was predominantly sensorineural.

Conclusion:

The main cause of otological symptoms (apart from otalgia) and of audiometric findings in temporomandibular disorder patients is postulated to be an altered middle-ear to inner-ear pressure equilibrium.