THE PATHOLOGY OF SEVERAL DISORDERS OF THE INNER EAR WHICH CAUSE VERTIGO

Linking Cerebrovascular Dysfunction to Age-Related Hearing Loss and Alzheimer’s Disease—Are Systemic Approaches for Diagnosis and Therapy Required?

Alzheimer’s disease (AD), the most common cause of dementia in the elderly, is a neurodegenerative disorder associated with neurovascular dysfunction, cognitive decline, and the accumulation of amyloid β peptide (Aβ) in the brain and tau-related lesions in neurons termed neurofibrillary tangles (NFTs). Aβ deposits and NFT formation are the central pathological hallmarks in AD brains, and the majority of AD cases have been shown to exhibit a complex combination of systemic comorbidities. While AD is the foremost common cause of dementia in the elderly, age-related hearing loss (ARHL) is the most predominant sensory deficit in the elderly. During aging, chronic inflammation and resulting endothelial dysfunction have been described and might be key contributors to AD; we discuss an intriguing possible link between inner ear strial microvascular pathology and blood–brain barrier pathology and present ARHL as a potentially modifiable and treatable risk factor for AD development. We present compelling evidence that ARHL might well be seen as an important risk factor in AD development: progressive hearing impairment, leading to social isolation, and its comorbidities, such as frailty, falls, and late-onset depression, link ARHL with cognitive decline and increased risk of dementia, rendering it tempting to speculate that ARHL might be a potential common molecular and pathological trigger for AD. Additionally, one could speculate that amyloid-beta might damage the blood–labyrinth barrier as it does to the blood–brain barrier, leading to ARHL pathology. Finally, there are options for the treatment of ARHL by targeted neurotrophic factor supplementation to the cochlea to improve cognitive outcomes; they can also prevent AD development and AD-related comorbidity in the future.

The Conspicuous Link between Ear, Brain and Heart-Could Neurotrophin-Treatment of Age-Related Hearing Loss Help Prevent Alzheimer's Disease and Associated Amyloid Cardiomyopathy?

Alzheimer's disease (AD), the most common cause of dementia in the elderly, is a neurodegenerative disorder associated with neurovascular dysfunction and cognitive decline. While the deposition of amyloid β peptide (Aβ) and the formation of neurofibrillary tangles (NFTs) are the pathological hallmarks of AD-affected brains, the majority of cases exhibits a combination of comorbidities that ultimately lead to multi-organ failure. Of particular interest, it can be demonstrated that Aβ pathology is present in the hearts of patients with AD, while the formation of NFT in the auditory system can be detected much earlier than the onset of symptoms. Progressive hearing impairment may beget social isolation and accelerate cognitive decline and increase the risk of developing dementia. The current review discusses the concept of a brain-ear-heart axis by which Aβ and NFT inhibition could be achieved through targeted supplementation of neurotrophic factors to the cochlea and the brain. Such amyloid inhibition might also indirectly affect amyloid accumulation in the heart, thus reducing the risk of developing AD-associated amyloid cardiomyopathy and cardiovascular disease.

Audiological Evaluation of Vestibular Schwannoma Patients with Normal Hearing

Objective: To evaluate the audiological aspects of vestibular schwannoma (VS) patients with normal hearing. Study Design: Retrospective study. Setting: Quaternary referral center for skull base pathologies. Patients: The records on 4,000 patients who had been diagnosed with VS between 1986 and December 2017 were retrospectively reviewed. The patients included in the study were the ones who complied with the strict audiological normality criteria, as follows: a pure tone hearing threshold (at the 6-octave-spaced frequencies from 250 to 8,000 Hz) ≤25 dBHL; a word recognition score >90%; and interaural differences ≤10 dB at each frequency. Interventions: Auditory brainstem response (ABR) testing and radiological imaging. Main Outcome Measures: The incidence of normal objective hearing among VS patients, and the diagnostic utility of the ABR and the effect of tumor size and site on the response. Results: The incidence of normal hearing among VS patients was 4.2%. Tinnitus and vertigo were the most common symptoms across tumor grades; 5.6% of the tumors were large and giant tumors. The ABR yielded a sensitivity of 73.6%, with a false negative rate of 26.3% using a cutoff point of 0.2 ms for interaural latency differences. Conclusions: The diagnosis of VS should not be based on audiometric thresholds alone. Alarming signs of VS should be clear to the physician in order not to miss or delay the diagnosis of the disease. The ABR is useful in the diagnosis of VS, but normal results do not exclude the occurrence of the disease in patients with normal hearing.

Recent advances in cochlear hair cell regeneration-A promising opportunity for the treatment of age-related hearing loss

The objective of this paper is to review current information regarding the treatment of age-related hearing loss by using cochlear hair cell regeneration. Recent advances in the regeneration of the inner ear, including the usefulness of stem cells, are also presented. Based on the current literature, cochlear cell regeneration may well be possible in the short term and cochlear gene therapy may also be useful for the treatment of hearing loss associated with ageing. The present review provide further insight into the pathogenesis of Inner Ear senescence and aged-related hearing loss and facilitate the development of therapeutic strategies to repair hair cells damaged by ageing. More research will be needed in order to translate them into an effective treatment for deafness linked to cochlear senescence in humans.

Reversible mechlorethamine-associated hearing loss in a patient with Hodgkin's disease

Mechlorethamine, when administered in massive doses (0.6-1.5 mg/kg) to cancer patients in several early studies, caused severe irreversible hearing loss. There have been no reports of ototoxicity with doses of 0.4 mg/kg or less. The authors describe a 36-year-old man who developed profound sensorineural hearing loss during his first cycle of MOPP chemotherapy for Hodgkin's disease. Cyclophosphamide was substituted for mechlorethamine in subsequent cycles and his hearing deficit resolved. This is the first reported case of reversible ototoxicity associated with currently recommended doses of mechlorethamine.

Bioelectric phenomena in the ototoxicity of nitrogen mustard

The effects of nitrogen mustard on the electrical potentials of the inner ear were studied, and the results were correlated with the histopathologic findings which have been reported in nitrogen mustard ototoxicity. The endocochlear DC potential (EP) decreased rapidly after an injection of nitrogen mustard (NM). The amplitude of the cochlear microphonics potential (CM) diminished rapidly, and no substantial recoveries were observed. No significant changes in the magnitude of the negative potential of organ of Corti (NPOC) were observed. A large negative summating potential (SP) was recorded even when the amplitude of the CM had diminished.

Electrical resistance of the cochlear partition

The relationship between the calculated value of the effective electrical resistance of the cochlear partition and the distance between the electrode for measuring the EP and the stimulating electrodes has been studied. The calculated value of the effective electrical resistance of the cochlear partition declines linearly with increasing distance between these electrodes. The correlation coefficient (r) is -0.806. In calculations of the effective electrical resistance of the cochlear partition, attention must be paid to the distance between the microelectrodes.

Degenerative changes in the human vestibular sensory epithelia

A study of the vestibular end organs from humans of different ages is presented. The inner ears were exposed by microdissection, and the vestibular sensory regions were either sectioned and studied with light or electron microscopy, or prepared and studied with the surface specimen technique. A change, which can be related to aging, is the accumulation of lipofuscin inclusions in sensory and supporting cells, especially pronounced in the type I sensory cell. Changes of the hair bundles, such as disarrangement of cilia, increased fragility of cilia and formation of giant cilia, have also been observed in aged individuals. In three cases there was a history of vestibular disturbance of vertigo. All three cases had shown caloric hypo-reactivity. In two cases, one with a history of herpes zoster oticus and another with a brain stem glioma, no morphological changes which could be attributed to the diseases, were found. The third case showed degeneration of macula utriculi and the lateral and superior cristae, possibly as a result of vascular disturbance.