Neuroinflammatory disorders of the brain and inner ear: a systematic review of auditory function in patients with migraine, multiple sclerosis, and neurodegeneration to support the idea of an innovative 'window of discovery'

Do Disinfectants Induce Ototoxicity and Cause Structural Damage to the Inner Ear?

BACKGROUND

This study examines the impact of commonly used disinfectants on hearing and the structural integrity of the inner ear.

OBJECTIVE

To evaluate the effects of indophor, alcohol, and chlorhexidine on auditory function and cochlear morphology in mice.

METHODS

Sixty-four mice were evenly divided into four groups: saline, indophor, alcohol, and chlorhexidine. Each mouse received a 25 μL injection of the designated liquid into the left ear, while the right ear was remained untreated. Auditory brainstem response (ABR) testing was performed at three intervals: before injection, 24 h post-injection, and one week post-injection. Cochlear tissues from both ears were analyzed using immunofluorescence and scanning electron microscopy to observe morphological changes.

RESULTS

Chlorhexidine and alcohol significantly increased ABR thresholds in the left ear 24 h and one week post-injection (p < 0.001). Chlorhexidine caused severe damage to outer hair cells, inner hair cells, and spiral ganglion cells, while alcohol had a milder effect. Iodophor mainly affected outer hair cells, with partial recovery after seven days. In the right ear, only chlorhexidine caused a sustained ABR threshold increase (p < 0.001) and severe damage to outer and inner hair cells. Both alcohol and chlorhexidine induced demyelination of spiral ganglion cells in the left ear, but recovery was seen only in the alcohol group after one week.

CONCLUSION

Indophor, alcohol, and chlorhexidine can all affect hearing, with alcohol and chlorhexidine causing more severe and lasting damage. These findings provide crucial insights for selecting disinfectants in ear surgeries.

LEVEL OF EVIDENCE

NA Laryngoscope, 135:2154-2163, 2025.

Isolated cranial nerve disorder as presenting sign in multiple sclerosis: optic nerve versus "the others"

Background

The prevalence of cranial nerve involvement in Multiple Sclerosis (MS) varies across studies. It has been speculated that first presentation of disease with cranial nerve involvement - except for optic neuritis - may be associated with milder progression.

Aim

This study compares the clinical outcome of patients with MS in a 4-year follow-up of patients with initial symptoms of optic neuritis (ON) versus those with other cranial nerve (OCN) involvement.

Materials and methods

Retrospective analysis of MS patient database of a tertiary referral university MS center. We included treatment-naïve patients diagnosed with MS according to the revised McDonald criteria, who presented with their first clinical symptoms suggestive of ON or OCN. Patients were required to have regular clinical and radiological follow-up visits (at least two outpatient visits per year and one annual 1.5T MRI), and no comorbidities. The number of relapses and the Expanded Disability Status Scale (EDSS) scores were assessed at six-month intervals during clinic visits. The primary outcome was the number of relapses observed during the study period, comparing the ON and OCN groups. Several statistical analyses were performed, including multiple linear regression, Cox proportional hazards model, one-way ANOVA, and odds ratios, to compare the groups.

Results

Of the 84 patients included, none had comorbities (e.g., overlap with other inflammatory diseases, neoplasm etc.). Fifty-five presented with ON and 29 with OCN (e.g., diplopia, trigeminal pain, hearing or vestibular symptoms) at onset. Patients with ON were younger than those with OCN symptoms (p = 0.02), had a higher risk of relapse (more than two relapses) (OR: 1.53) and greater disability (incremental EDSS) over the 4-year follow-up (OR: 1.60).

Conclusion

Patients with OCN involvement at the onset experienced fewer relapses and had better EDSS scores at the 4-year follow-up compared to those with ON at onset. These preliminary findings suggest that MS onset with OCN involvement may be associated with a more favorable disease course.

Feline atopic syndrome: An insight into its effects on the central nervous system through vestibular disease

A 2-year-old male Abyssinian cat was presented with a left head tilt, lethargy, compulsive walking with a left-circling tendency, medial strabismus, a delayed pupillary light reflex, abdominal papules, and severe pruritus that began at 4 mo of age. Imaging revealed mineral opacity foci in the left ear, and magnetic resonance imaging confirmed heterogeneous signal changes, suggesting a diagnosis of otitis interna. No abnormal findings were observed on cerebrospinal fluid tests. Treatment with prednisolone, antibiotics, a hypoallergenic diet, and probiotics led to the resolution of skin issues and neurological improvement. Despite a persistent head tilt after more than 5 mo, there was no recurrence of severe neurological symptoms during the tapering off of prednisolone treatment. Key clinical message: This is the first case report illustrating the potential impact of feline atopic syndrome on the central nervous system. It emphasizes the importance of viewing feline atopic syndrome as more than just a skin disorder.

Hypothetical criteria and types for cochlear migraine

Cochlear migraine (CM) and cochleovestibular migraine were first reported in 2018. However, the diagnostic criteria and types of CM were still undefined. We proposed a hypothetical criteria for CM as below: A. At least 2 episodes with cochlear symptoms with or without recovery. B. Current or previous history of migraine with or without aura according to the International Classification of Headache Disorders-3. C. One or more migraine features with at least 50% of the cochlear episodes. D. No current or previous history of vestibular symptoms. E. Not better accounted for by another cochlear or International Classification of Headache Disorders-3 diagnosis. Patients who were fitted with all 5 points could be diagnosed as CM. The clinical presentations of 62 adults with CM were included for descriptive and cluster analysis. There were 20 men and 42 women, with an age range of 27 to 72 years (mean, 50 years). 6 patients had migraine with aura, and the other 56 had migraine without aura. 4 types of CM could be categorized by cluster analysis. Type 1: unilateral fluctuating sensorineural hearing loss (SNHL) with or without tinnitus (35.5%). Type 2: repeated idiopathic sudden SNHL with or without tinnitus, with good recovery (22.6%). Type 3: idiopathic sudden SNHL with or without tinnitus, but deteriorated over time (21.0%). Type 4: unilateral fluctuating tinnitus with or without aural fullness, otalgia or mild SNHL (21.0%). We hope to raise more discussion about the criteria and clinical types of CM and/or cochleovestibular migraine.

Hearing Loss and Alzheimer Disease

Several studies have been done to investigate the role of hearing loss (HL) in cognitive decline. A co-existence of these two conditions has been identified. Recently, thanks to the use of functional MRI and EEG it has been shown that untreated HL can expose patients with cognitive decline to a higher risk of developing Alzheimer Disease (AD). This chapter will discuss the difference between central and peripheral HL, the link between HL and cognition and the relationship between HL and AD. At the end of the chapter the available technologies to treat HL will be discussed as well as their impact on memory and cognition.

The bidirectional brain-cochlea axis: a scaffold for neurologic disease-associated hearing loss

This scientific commentary refers to 'Beyond the cochlea: exploring the multifaceted nature of hearing loss in primary mitochondrial diseases', by Koohi et al. (https://doi.org/10.1093/braincomms/fcae374).

Exploring Inner Ear and Brain Connectivity through Perilymph Sampling for Early Detection of Neurological Diseases: A Provocative Proposal

Recent evidence shows that it is possible to identify the elements responsible for sensorineural hearing loss, such as pro-inflammatory cytokines and macrophages, by performing perilymph sampling. However, current studies have only focused on the diagnosis of such as otologic conditions. Hearing loss is a feature of certain neuroinflammatory disorders such as multiple sclerosis, and sensorineural hearing loss (SNHL) is widely detected in Alzheimer's disease. Although the environment of the inner ear is highly regulated, there are several communication pathways between the perilymph of the inner ear and cerebrospinal fluid (CSF). Thus, examination of the perilymph may help understand the mechanism behind the hearing loss observed in certain neuroinflammatory and neurodegenerative diseases. Herein, we review the constituents of CSF and perilymph, the anatomy of the inner ear and its connection with the brain. Then, we discuss the relevance of perilymph sampling in neurology. Currently, perilymph sampling is only performed during surgical procedures, but we hypothesize a simplified and low-invasive technique that could allow sampling in a clinical setting with the same ease as performing an intratympanic injection under direct visual check. The use of this modified technique could allow for perilymph sampling in people with hearing loss and neuroinflammatory/neurodegenerative disorders and clarify the relationship between these conditions; in fact, by measuring the concentration of neuroinflammatory and/or neurodegenerative biomarkers and those typically expressed in the inner ear in aging SNHL, it could be possible to understand if SNHL is caused by aging or neuroinflammation.

Vestibular migraine: an update

PURPOSE OF REVIEW

We performed a narrative review of the recent findings in epidemiology, clinical presentation, mechanisms and treatment of vestibular migraine.

RECENT FINDINGS

Vestibular migraine is an underdiagnosed condition that has a high prevalence among general, headache and neuro-otology clinics. Vestibular migraine has a bimodal presentation probably associated with a hormonal component in women. These patients could have a complex clinical phenotype including concomitant autonomic, inflammatory or connective tissue conditions that have a higher prevalence of psychological symptoms, which may mistakenly lead to a diagnosis of a functional neurological disorder. A high proportion of patients with postural perceptual persistent dizziness have a migraine phenotype. Independently of the clinical presentation and past medical history, patients with the vestibular migraine phenotype can respond to regular migraine preventive treatments, including those targeting the calcitonin gene-related peptide pathways.

SUMMARY

Vestibular migraine is an underdiagnosed migraine phenotype that shares the pathophysiological mechanisms of migraine, with growing interest in recent years. A thorough anamnesis is essential to increase sensitivity in patients with unknown cause of dizziness and migraine treatment should be considered (see supplemental video-abstract).