Vestibular Disorders and Hormonal Dysregulations: State of the Art and Clinical Perspectives

The interaction between endocrine and vestibular systems remains poorly documented so far, despite numerous observations in humans and animals revealing direct links between the two systems. For example, dizziness or vestibular instabilities often accompany the menstrual cycle and are highly associated with the pre-menopause period, while sex hormones, together with their specific receptors, are expressed at key places of the vestibular sensory network. Similarly, other hormones may be associated with vestibular disorders either as causal/inductive factors or as correlates of the pathology. This review was carried out according to the PRISMA method, covering the last two decades and using the MEDLINE and COCHRANE databases in order to identify studies associating the terms vestibular system and/or vestibular pathologies and hormones. Our literature search identified 646 articles, 67 of which referred directly to vestibular dysfunction associated with hormonal variations. While we noted specific hormonal profiles depending on the pathology considered, very few clinical studies attempted to establish a direct link between the expression of the vestibular syndrome and the level of circulating hormones. This review also proposes different approaches to shed new light on the link between hormones and vestibular disorders, and to improve both the diagnosis and the therapeutic management of dizzy patients.

Ductus Reuniens and Its Possible Role in Menière's Disease

OBJECTIVE

After 160 years the true underlying cause of Meniere's disease remains enigmatic. The aim of our study is to discuss the possible implication of an obstruction of the ductus reuniens as a cause in Menière's disease.

METHODOLOGY

We first conducted an historical study of the description of the ductus reuniens. We then reviewed the literature regarding ductus reuniens obstruction in animal experiments, human post-mortem studies and living ear imaging. We completed its description by modern microCT imaging. Limited knowledge on the fate of dislodged saccular otoconia is summarized. The possible implications for Meniere's attacks are discussed.

RESULTS

Victor Hensen was the first to describe the ductus reuniens in 1863. He described its length and width and predicted that saccular otoconia might enter the ductus and the cochlea. On microCT the narrowest width of the human ductus reuniens was 0.14 mm. The literature reports cochlear endolymphatic hydrops occurring after animal experimental obstruction of the duct. Human postmortem studies have confirmed saccular otoconial clumps entering the ductus and the cochlea. A postmortem study has shown sites of endolymphatic obstruction, and imaging speculates on blockages in ears with Meniere's disease. Dislodged utricular otoconia can be in clumps of otolithic membranes.

CONCLUSION

Blockages of the ductus reuniens and at other endolymphatic system sites appear to be a feature in Meniere's disease ears. The blockages have been postulated to be saccular otoconia either causing or aggravating hydrops. This could be consistent with observed nystagmus reversals during attacks as the endolymphatic sac attempts to clear the hydrops and the otoconia.

The proteome of the human endolymphatic sac endolymph

The endolymphatic sac (ES) is the third part of the inner ear, along with the cochlea and vestibular apparatus. A refined sampling technique was developed to analyse the proteomics of ES endolymph. With a tailored solid phase micro-extraction probe, five ES endolymph samples were collected, and six sac tissue biopsies were obtained in patients undergoing trans-labyrinthine surgery for sporadic vestibular schwannoma. The samples were analysed using nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) to identify the total number of proteins. Pathway identification regarding molecular function and protein class was presented. A total of 1656 non-redundant proteins were identified, with 1211 proteins detected in the ES endolymph. A total of 110 proteins were unique to the ES endolymph. The results from the study both validate a strategy for in vivo and in situ human sampling during surgery and may also form a platform for further investigations to better understand the function of this intriguing part of the inner ear.

[Various types of vertigo and balance disorders in patients with Meniere's disease]

Vertigo and balance disorders in Meniere's disease (MD) may have various etiology. The aim of the review is discussing pathogenetic mechanisms of the typical vertiginous paroxysms in MD, resulting from endolymphatic hydrops as well as analysis of etiology, pathogenesis, clinical course and basic treatment of paroxysmal and permanent forms of vertigo and balance disorders, caused by other conditions, associated with MD. We discussed the course of MD complicated by vestibular migraine, benign positional paroxysmal vertigo, functional dizziness, bilateral vestibulopathy and vestibular drop-attacks.

A Micro-CT and Synchrotron Imaging Study of the Human Endolymphatic Duct with Special Reference to Endolymph Outflow and Meniere's Disease

Meniere’s disease remains enigmatic, and has no treatment with sufficient evidence. The characteristic histopathological finding is endolymphatic hydrops, suggesting either an overproduction or decreased reabsorption of endolymph in the human inner ear. This study presents the first analysis of the vascular plexus around the human endolymphatic duct using micro computed tomography and coherent synchrotron radiation with phase contrast imaging. Using a software program, data were processed by volume-rendering with scalar opacity mapping to create transparent three-dimensional reconstructions. A rich vascular plexus was discovered around the endolymphatic duct that drained into collecting channels, linked to the vestibular venous outflow system. This network is believed to make up the principal route for endolymph outflow, and its associated malfunction may result in endolymphatic hydrops and Meniere’s disease.

The cardiovascular aspects of a Ménière's disease population - A pilot study

INTRODUCTION

MD is considered a rare disease. An adequate model that explains MD's pathophysiology is not well established. Recently, the vascular theory of the disease has been revived.

OBJECTIVES

To characterize a MD population according to its cardiovascular risk and correlate it to the MD clinical course.

METHODS

In this retrospective chart study the data of 31 MD patients observed between January 2017 and April 2018 in a tertiary university hospital were reviewed. Patients included in the study were diagnosed according to the Bárány Society criteria. Lost follow-ups, patients with autoimmune disease, atopy or allergy, major psychiatric disease and migraine were excluded. Age, gender, cardiovascular risk factors, audiometric and vestibular parameters, occurrence of MD attacks in the previous 6 months, vestibular medication in course and time course of MD were recorded and compared between groups (with and without cardiovascular risk factors).

RESULTS

31 patients (61.3% females) mean aged 60.3 years (±9.7) were studied. 74% of the population had at least one risk factor and 51.6% of patients had attacks in the last 6 months. There was a statistically significant difference in the occurrence of MD attacks in the last 6 months (p = 0.014) between MD patients with and without risk factors. Mean PTA thresholds were higher and speech discrimination was lower in individuals with more cardiovascular risk factors.

CONCLUSIONS

Treatment of MD focusing on vascular risk factors may allow a better control of symptoms and result in a decreased need for ablative procedures in this disorder.

Gadolinium-enhanced MRI reveals dynamic development of endolymphatic hydrops in Ménière's disease

INTRODUCTION

Meniere's disease is associated with impaired hearing, tinnitus, vertigo, and aural fullness. Many anatomical studies have suggested idiopathic endolymphatic hydrops as the pathological basis of Meniere's disease, which now can be visualized by using gadolinium -enhanced magnetic resonance imaging of the inner ear.

OBJECTIVE

To investigate the development of endolymphatic hydrops in Meniere's disease by monitoring the vestibules and cochleae of affected patients.

METHODS

Inner ears of 178 patients with definite unilateral Meniere's disease diagnosis were visualized by 3-dimensional fluid-attenuated inversion recovery and three-dimensional real inversion recovery magnetic resonance imaging following bilateral gadolinium intratympanic injection. The scans were used to evaluate the presence and degree of endolymphatic hydrops in the vestibules and cochlear structures, including the cochlear apical turn, the cochlear middle turn, and the cochlear basal turn. The correlation of endolymphatic hydrops occurrence between the various parts of the inner ear was determined.

RESULTS

Symptomatic endolymphatic hydrops was detected on the affected side in all patients, whereas asymptomatic endolymphatic hydrops was detected on the unaffected contra-lateral side in 32 patients (18.0%). On the affected side, the cochlear apical turn and the cochlear middle turn demonstrated significantly higher rates of endolymphatic hydrops than the cochlear basal turn and the vestibule. The severity of endolymphatic hydrops gradually decreased from the cochlear apical turn to the cochlear basal turn. On the contra lateral side, the incidence and degree of the detected asymptomatic endolymphatic hydrops were significantly greater in the cochleae than in the vestibules (p<0.05), with no significant difference detected between the cochlear turns.

CONCLUSION

Progression of endolymphatic hydrops appears to be directional, initiated in the cochlea. The order of endolymphatic hydrops severity gradually decreases from the cochlear apical turn to the cochlear basal turn and then to the vestibule. Endolymphatic hydrops in the vestibule is associated with symptomatic Meniere's disease.

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.

Current Treatment of Endolymphatic Sac Tumor of the Temporal Bone

An endolymphatic sac tumor (ELST) is a rare, indolent but locally aggressive tumor arising in the posterior petrous ridge. Patients present with sensorineural hearing loss and tinnitus. As the tumor progresses, patients may experience vertigo, ataxia, facial nerve paresis, pain and otorrhea. Most patients present in their 4th or 5th decade with a wide age range. Patients with von Hippel-Lindau disease have an increased likelihood of developing ELST. Histologically, ELST is a low-grade adenocarcinoma. As it progresses, it destroys bone and extends into adjacent tissues. The likelihood of regional or distant metastases is remote. The optimal treatment is resection with negative margins. Patients with positive margins, gross residual disease, or unresectable tumor are treated with radiotherapy or radiosurgery. Late recurrences are common, so long follow-up is necessary to assess efficacy. The likelihood of cure depends on tumor extent and is probably in the range of 50-75%.

Genetics of guanylyl cyclase pathways in the cochlea and their influence on hearing

Although hearing loss is the most common sensory deficit in Western societies, there are no successful pharmacological treatments for this disorder. Recent experiments have demonstrated that manipulation of intracellular cyclic guanosine monophosphate (cGMP) concentrations can have both beneficial and harmful effects on hearing. In this review, we will examine the role of cGMP as a key second messenger involved in many aspects of cochlear function and discuss the known functions of downstream effectors of cGMP in sound processing. The nitric oxide-stimulated soluble guanylyl cyclase system (sGC) and the two natriuretic peptide-stimulated particulate GCs (pGCs) will be more extensively covered because they have been studied most thoroughly. The cochlear GC systems are attractive targets for medical interventions that improve hearing while simultaneously representing an under investigated source of sensorineural hearing loss.