Immune Mechanisms In Meniere’s Syndrome

A Perspective for Ménière’s Disease: In Silico Investigations of Dexamethasone as a Direct Modulator of AQP2

Ménière’s disease is a chronic illness characterized by intermittent episodes of vertigo associated with fluctuating sensorineural hearing loss, tinnitus and aural pressure. This pathology strongly correlates with a dilatation of the fluid compartment of the endolymph, so-called hydrops. Dexamethasone is one of the therapeutic approaches recommended when conventional antivertigo treatments have failed. Several mechanisms of actions have been hypothesized for the mode of action of dexamethasone, such as the anti-inflammatory effect or as a regulator of inner ear water homeostasis. However, none of them have been experimentally confirmed so far. Aquaporins (AQPs) are transmembrane water channels and are hence central in the regulation of transcellular water fluxes. In the present study, we investigated the hypothesis that dexamethasone could impact water fluxes in the inner ear by targeting AQP2. We addressed this question through molecular dynamics simulations approaches and managed to demonstrate a direct interaction between AQP2 and dexamethasone and its significant impact on the channel water permeability. Through compartmentalization of sodium and potassium ions, a significant effect of Na+ upon AQP2 water permeability was highlighted as well. The molecular mechanisms involved in dexamethasone binding and in its regulatory action upon AQP2 function are described.

Pathogenesis and Etiology of Ménière Disease: A Scoping Review of a Century of Evidence

Importance

Ménière disease is a rare chronic benign disorder of the inner ear with a natural history of multiple clinical phenotypes of variable severity and a tendency to burnout with time. Although multiple treatment modalities have been shown to improve the disease process-some adversely affecting cochleovestibular function-it remains uncertain whether one, several separate, or a combination of pathophysiologic mechanisms affect the disease process. A scoping review of the evidence underlying proposed pathophysiologic mechanisms of Ménière disease is needed to determine which processes are most likely to be etiopathogenic factors.

Observations

Of the 4602 relevant articles found through Embase, Ovid, and PubMed, 444 met inclusion criteria. The most common reported causes of Ménière disease were autoimmune or immune-mediated, genetic, or structural dysfunction of the inner ear. During the study period from inception to March 2021, etiologic theories shifted from structural dysfunction to autoimmune and genetic causes of Ménière disease.

Conclusions and Relevance

This scoping review found that Ménière disease is a multifactorial disease with lifelong comorbidities and loss of quality-associated life-years whose most commonly reported causes were structural dysfunction, immunologic damage, and genetic susceptibility. Recent studies have examined how autoinflammatory processes and vestibular migraine may be associated with Ménière disease. Large heterogeneity among studies may be explained by historical differences in the clinical understanding of the disease, as well as evolving intervention methodologies and practitioner expertise. Ménière disease is a multifactorial disease with lifelong comorbidities and loss of quality-associated life-years; therefore, future studies of reliable biomarkers of endolymphatic hydrops and real-time imaging are warranted to improve understanding and treatment.

Autoimmune vertigo: an update on vestibular disorders associated with autoimmune mechanisms

The role of the immune system in mediating cochleovestibular pathologies has received increasing attention in recent years. Autoimmune vertigo may be an invalidating condition and may worsen the quality of life of affected patients, especially in the cases of delayed diagnosis. Since the etiopathogenesis is still not clear, also the treatment is not yet completely delineated. According to the clinical presentation, autoimmune vertigo can present as an isolated disorder or in association with systemic autoimmune diseases. The main feature in autoimmune vertigo is the presence of an abnormal immune response, in either absence or presence of systemic autoimmune disease, directed against delicate components of the inner ear. This may determine a functional or anatomical alteration, with an inflammatory reaction often devastating for hearing and balance. Being the exact pathogenesis unknown, the diagnosis of autoimmune vertigo is based either on clinical criteria or on a positive response to steroids. The earlier the diagnosis is made, the sooner the therapy can be installed, giving a chance to the recovery of inner ear damages. Corticosteroids represent the most effective and universally accepted treatment, even if other immunomodulatory drugs are now having a more extensive use. HIGHLIGHTS: Vertigo is relatively frequent in autoimmune diseases; however, it is often misdiagnosed or attributed to central nervous system alterations rather to specific inner ear involvement. Vertigo and other audiovestibular symptoms may be the first manifestation of an autoimmune disease and if correctly addressed could significantly contribute to early diagnosis of the underlying autoimmune disease. Early diagnosis of immune-related vertigo can lead to prompt initiation of targeted therapy with elevate chances of preventing irreversible damages to the inner ear. The presence of alternating phases of well-being and disabling symptoms in patients with vertigo should always been considered, as they could suggest an underlying autoimmune condition.

Investigation of high-frequency hearing loss and outer hair cell function of the cochlea in patients with psoriasis: a case-control study

The inner ear can be the target of autoimmune attacks, and sensorineural hearing loss can occur as a complication in various non-organ-specific autoimmune diseases. The aim of this study was to compare cochlear functions and hearing evaluation in patients with psoriasis and controls. In total, 29 patients with psoriasis and 30 healthy controls (HCs) were included in the study. Pure-tone audiometry at 250, 500, 1000, 2000, 4000, 8000, 10 000, 12 000, 14 000 and 16 000 Hz was performed for patients as HCs, as were immittance measures including tympanometry, acoustic reflex and otoacoustic emission testing. There were statistically significant (P < 0.05) differences between patients and HCs for pure-tone thresholds at high frequencies, and for distortion product otoacoustic emission (DPOAE) responses and signal : noise ratio at all frequencies. In our study, based on DPOAE and audiological findings, there was damage to the outer hair cells of the cochlea, resulting in high-frequency hearing loss in patients with psoriasis.

Mean platelet volume, red cell distribution width, platelet-to-lymphocyte and neutrophil-to-lymphocyte ratios in patients with ankylosing spondylitis and their relationships with high-frequency hearing thresholds

The mean platelet volume (MPV), red cell distribution width (RDW) and neutrophil-to-lymphocyte ratio (NLR) comprise laboratory markers in ankylosing spondylitis (AS). There is a controversy in the literature regarding which type of ear involvement is characteristic of AS. The aim of this study was to simultaneously investigate the MPV, RDW, platelet to lymphocyte (PLR) and NLR in patients with AS and their relationships with high-frequency hearing thresholds. Thirty patients with AS and 35 age-matched healthy subjects were included. Each subject was tested with low- (250, 500, 1000 and 2000 Hz) and high- (4000, 8000, 10,000, 12,000, 14,000 and 16,000 Hz) frequency audiometry. Additionally, the case and control groups were evaluated regarding the average hearing thresholds in bone conduction. The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels were measured. The RDW, MPV, neutrophils, lymphocytes and platelet counts were evaluated with the complete blood count. Furthermore, the NLR and PLR were calculated. The complete blood count, platelet numbers, ESR, CRP and NLR levels were significantly increased in the AS patients compared with the healthy controls (p < 0.001, p = 0.007, p < 0.001, p < 0.001 and p = 0.047, respectively). There was no statistically significant difference in the RDW, PLR or MPV levels (p > 0.05) in the AS patients compared with the healthy controls. The BASDAI score and disease duration were not correlated with the ESR, CRP levels, MPV, PLR, RDW or NLR in patients with AS (all; p > 0.05). The AS patients had increased average measurement values for the hearing threshold in both ears at frequencies of 250, 500, 1000 and 2000 Hz; however, there was no statistically significant difference (p > 0.05). The average values of the hearing threshold in both ears at the high frequencies of 4000, 6000, 8000, 10,000, 12,000 and 14,000 Hz were significantly increased in the case group; however, it was not significantly increased at 16,000 Hz. The current study is the first to investigate the PLR, NLR, MPV and RDW levels in acute AS. We identified a significantly increased NLR, leukocyte count, ESR and CRP in AS patients. Sensorineural hearing loss, especially at extended high frequencies, is common in patients with AS and may represent an extra-articular feature of the disease. The combined use of NLR with the leukocyte count and other clinical assessments may facilitate the diagnostic process of ankylosing spondylitis.

Vestibular disorders in euthyroid patients with Hashimoto's thyroiditis: role of thyroid autoimmunity

INTRODUCTION

A relationship between vestibular disorders and thyroid autoimmunity independently from thyroid function has been postulated.

AIM

To shed more light on the actual relationship between vestibular lesions and Hashimoto's thyroiditis (HT) regardless of thyroid function.

METHODS

Forty-seven patients with HT (89·4% F; aged 48·3 ± 12·7 years), 21 with multinodular goitre (MNG; 57·1% F; 54·1 ± 9·8 years) and 30 healthy volunteers (56·7% F; 50·7 ± 13·9 years) were enrolled. Inclusion criteria were the presence of normal thyroid function tests and no clinical history of vestibular dysfunction. Each subject was submitted to complete vestibular evaluation [Caloric Test, Vestibular evoked myogenic potentials (VEMPs), Head Shaking Test (HST)].

RESULTS

52·2% of HT patients showed an alteration of VEMPs and 44·7% of caloric test (P < 0·0001 for both). None of the MNG patients showed any vestibular alteration, while one healthy control showed an altered caloric test. A correlation was found between vestibular alterations of HT patients and the degree of serum TPOAb level, not affected by age and serum TSH value. By logistic regression analysis, the absence of thyroid autoimmunity significantly reduced the risk of vestibular alterations: HR 0.19 (95%CI: 0·003-0.25, P = 0·0004) for caloric test; HR 0·07 (95%CI: 0·02-0·425, P < 0·0001) for VEMPs; and HR 0·22 (95%CI: 0·06-0·7, P = 0·01) for HST.

CONCLUSION

In euthyroid HT patients, a significant relationship between subclinical vestibular damage and the degree of TPOAb titre was documented. This finding suggests that circulating antithyroid autoantibodies may represent a risk factor for developing vestibular dysfunction. An accurate vestibular evaluation of HT patients with or without symptoms is therefore warranted.

Meniere's disease might be an autoimmune condition?

OBJECTIVES

To review our current knowledge of the pathogenesis of Meniere's disease, including viral infection and immune system-mediated mechanisms, and to discuss the pathogenesis as it relates to pharmacotherapy.

SYSTEMATIC REVIEW METHODOLOGY

Relevant publications on the aetiopathogenesis, molecular biology, genetics and histopathology of Meniere's disease from 1861 to 2011 were analysed.

RESULTS AND CONCLUSIONS

Meniere's disease is characterised by intermittent episodes of vertigo, fluctuating sensorineural hearing loss, tinnitus, and aural pressure. The aetiology and pathogenesis remain unknown. Proposed theories of causation include viral infections and immune system-mediated mechanisms. The immune response in Meniere's disease is focused on inner ear antigens. Approximately one-third of Meniere's disease cases seem to be of an autoimmune origin although the immunological mechanisms involved are not clear. The diagnosis of autoimmune inner ear disease is based either on clinical criteria or on a positive response to steroids. The antiviral approach has virtually eliminated the use of various surgical methods used in the past. Steroid responsiveness is high, and with prompt treatment, inner ear damage may be reversible. The administration of etanercept improves or stabilises symptoms in treated patients. Treatment of antiphospholipid syndrome can be directed toward preventing thromboembolic events by using antithrombotic medications. Only warfarin has been shown to be effective. Gene therapy can be used to transfer genetic material into inner ear cells using viral vectors and to protect, rescue, and even regenerate hair cells of the inner ear.

Possible association between thyroid autoimmunity and Menière's disease

Various aetiopathological mechanisms have been postulated to be at the root of Menière's disease (MD), and some data suggest that there may be also an underlying autoimmune factor. In fact, Menière patients manifest certain characteristics that are typical of autoimmune involvement association of particular human leucocyte antigen haplotypes, the presence of antibodies against internal ear antigens. In this study, we evaluated the association between thyroid autoimmunity and MD in a non-selected group of patients. We recruited 50 consecutive MD patients and two groups as controls: group A, 82 healthy volunteers; and group B, 50 subjects suffering from acute unilateral peripheral vestibulopathy. All subjects were submitted to instrumental assessment of cochlear-vestibular function and analysis of thyroid-stimulating hormone (TSH), free triiodothyronine, free thyroxine, anti-TSH receptor antibody (TR-Ab), anti-thyroperoxidase antibody (TPO-Ab) and anti-thyroglobulin antibody (Tg-Ab) in the blood. The prevalence of autoimmune thyroiditis in group B [6/50 (12%); 66.7% TPO-Ab and 33.3% Tg-Ab] was superimposable with the healthy controls [6/82 (7%); 66.7% TPO-Ab and 33.3% Tg-Ab]. In contrast, 38% of the MD patients (P = 0.0001 versus group A and group B) had significant autoantibody levels (68.4% TPO-Ab; 15.8% TPO-Ab + TR-Ab; 10.5% Tg-Ab; 5.2% TPO-Ab + Tg-Ab). Furthermore, 14% of the MD patients were hyperthyroid under l-thyroxine therapy, while no dysfunction was seen in the control groups. Overall, our data demonstrate a significant association between MD and thyroid autoimmunity, which suggests that an autoimmune factor is involved in the aetiopathogenesis of this disease. These findings suggest that it should be useful to submit MD patients to multi-disciplinary clinical investigation.

Antibodies to inner ear antigens in Meniere's disease

Meniere's disease (MD) is an idiopathic inner ear disorder characterized by fluctuating hearing loss, episodic vertigo and tinnitus. Its aetiology is unknown, although there is growing evidence that autoimmunity may be involved in its development. Using the Western blot immunoassay, we examined the reactivity to bovine inner ear antigens of sera from a series of MD patients who had previously been extensively studied for the presence of antibodies to collagens and membrane proteins. Reactivity to inner ear antigens of molecular weight 44 and 53 kD was found in 11/25 (44%) and 10/25 (40%) of the patients, respectively; both antigens were absent in the sera of healthy donors. It is still unclear whether the antibodies to 44 and 53 kD proteins play a role in the pathogenesis of MD or if they instead represent the result of inflammation and tissue destruction. Even if the latter is true, they may contribute to the perpetuation of the disease or play a role as a cofactor in association with other mechanisms.

Demyelination of Vestibular Nerve Axons in Unilateral Ménière's Disease

We conducted a study to determine whether vestibular nerves inpatients with unilateral Ménière's disease whose symptoms are refractory to medical management exhibit neuropathologic changes. We also endeavored to determine whether retrocochlear abnormalities are primary or secondary factors in the disease process. To these ends, we obtained vestibular nerve segments from five patients during retrosigmoid (posteriorfossa) neurectomy, immediately fixed them, and processed them for light and electron microscopy. We found that all five segments exhibited moderate to severe demyelination with axonal sparing. Moreover, we noted that reactive astrocytes produced an extensive proliferation of fibrous processes and that the microglia assumed a phagocytic role. We conclude that the possible etiologies of demyelination include viral and/or immune-mediated factors similar to those seen in other demyelinating diseases, such as multiple sclerosis and Guillain-Barré syndrome. Our findings suggest that some forms of Ménière's disease that are refractory to traditional medical management might be the result of retrocochlear pathology that affects the neuroglial portion of the vestibular nerve.

Pathology and pathophysiology of Meniere's disease

Histopathologic study of the human temporal bone entails microscopic examination and analysis of a series of histologic sections. This is currently the most effective method for observing the pathologic conditions of MD by examining the entire inner ear. Complete temporal bone histopathology cannot be replaced by either clinical pathologic study of small biopsy specimens obtained during surgery, or experimental animal studies that can create endolymphatic hydrops but not create MD. We believe that the histopathologic findings together with clinical information on MD is valuable in enhancing our understanding of the pathophysiology of the inner ear in MD. For example, a hypoplastic VA and ES in MD seem to indicate that there may be congenital predisposing factors in the development of MD. The exact pathologic findings characteristic of MD remains unclear, however. Many of the temporal bone specimens were obtained years after patients were diagnosed with MD and those specimens were involved with moderate postmortem changes. For these reasons, further collection of temporal bone specimens with fewer postmortem changes, obtained within a shorter premortem time period between occurrence of the disease and the time of the patients' death, and from patients with a well-characterized clinical history of MD, is imperative. Contemporary temporal bone studies now include in situ hybridization histochemistry or polymerase chain reaction (PCR) analysis for protein, enzymes, or viral antigens that can be directed at specimens from patients with MD [54,55]. It is hoped that in the near future such advanced research studies with human temporal bone histology sections will support and enhance the significant contribution of temporal bone histopathology to clinical otology.

Menière's disease: pathophysiology and treatment

Menière's disease is defined by the association of 4 symptoms: vertigo attacks, fluctuating hearing loss, tinnitus and an auricular plenitude sensation. The pathophysiology is commonly explained by a distension of membranous labyrinth by the endolymph, equally called endolymphatic hydrops. Recent studies also tend to relate the disease to immune mechanisms. The treatment is medical in the majority of patients but there is no international consensus on the management of the different stages of Menière's disease. Regarding the lack of clinical studies clearly demonstrating the effectiveness of a certain therapy or another. the recommendations are usually based on the empirical experience of practitioners and on the observation of a marked amelioration at 2 years of treatment in the majority of patients. The treatment of the acute phase of Menière's disease is basically symptomatic. Vestibular suppressant drugs have a well-established record in controlling acute attacks of vertigo. Most have variable anticholinergic, anti-emetic and vestibular sedative effects. If necessary, the administration of benzodiazepines will help to alleviate anxiety. Long term management of Menière's disease includes a low salt diet, the use of diuretics in the post-crisis phase, and the very common use in Europe of histaminergic agents. Corticosteroids are used in bilateral forms of Menière's disease, particularly if an autoimmune basis is suspected. All authors insist on the interest and the importance of regular follow-up, especially with regard to the psychological status and responsiveness to treatment of the patient. Surgical indications are rare and the least invasive procedures are used first. The choice of the procedure should take into consideration the need to preserve the auditory function of the patient.

Low-dose Oral Methotrexate Management of Patients with Bilateral Ménière's Disease

In this retrospective clinical trial, we evaluated the effectiveness of low-dose oral methotrexate in the management of bilateral Ménière's disease of immune-mediated origin. At our tertiary-care referral center, we evaluated ten men and eight women who had longstanding bilateral Ménière's disease that had been unresponsive to traditional conservative medical management. Sixteen of these patients had steroid-responsive bilateral Ménière's disease. Two patients had contraindications to steroids, but their clinical and laboratory evaluations were consistent with an immune-mediated process.

Patients were treated with 7.5 to 20 mg/week of oral methotrexate. The mean duration of treatment was 16.7 months (range: 8 to 35), with a mean followup of 2 years (range: 9 mo to 5 yr). Changes in clinical symptoms (vertigo, hearing loss, tinnitus, and aural fullness), audiometric changes, and side effects of therapy were evaluated.

Vertigo resolved in 14 patients (78%), was substantially alleviated in three patients (17%), and remained unchanged in one patient (6%). Hearing improved in five patients (28%) and stabilized in seven patients (39%). Tinnitus and aural fullness resolved or was relieved in 11 of 17 (65%) and 13 of 14 (93%) patients, respectively. Side effects were minimal and reversible.

We conclude that low-dose oral methotrexate is effective and safe for treating bilateral Ménierè's disease of immune-mediated origin. In this study, methotrexate alleviated vertiginous symptoms and improved or stabilized hearing in most patients. Low-dose methotrexate can be considered for patients with immune-mediated bilateral Meniérè's disease when long-term treatment is required or when a steroid or cyclophosphamide is contraindicated.