A multicenter study was set up to elucidate the environmental and medical risk factors contributing to age-related hearing impairment (ARHI). Nine subsamples, collected by nine audiological centers across Europe, added up to a total of 4,083 subjects between 53 and 67 years. Audiometric data (pure-tone average [PTA]) were collected and the participants filled out a questionnaire on environmental risk factors and medical history. People with a history of disease that could affect hearing were excluded. PTAs were adjusted for age and sex and tested for association with exposure to risk factors. Noise exposure was associated with a significant loss of hearing at high sound frequencies (>1 kHz). Smoking significantly increased high-frequency hearing loss, and the effect was dose-dependent. The effect of smoking remained significant when accounting for cardiovascular disease events. Taller people had better hearing on average with a more pronounced effect at low sound frequencies (<2 kHz). A high body mass index (BMI) correlated with hearing loss across the frequency range tested. Moderate alcohol consumption was inversely correlated with hearing loss. Significant associations were found in the high as well as in the low frequencies. The results suggest that a healthy lifestyle can protect against age-related hearing impairment.Electronic supplementary materialThe online version of this article (doi: 10.1007/s10162-008-0123-1) contains supplementary material, which is available to authorized users.

A simple three-stage grading system was acceptable for hydrops in both the vestibule and the cochlea: none, mild, and significant. In the vestibule, the grading was determined by the ratio of the area of endolymphatic space to the vestibular fluid space (sum of the endolymphatic and perilymphatic spaces). Patients with no hydrops have a ratio of one-third or less, those with mild hydrops have between one-third and a half, and those with significant hydrops have a ratio of more than 50%. In the cochlea, patients classified as having no hydrops show no displacement of Reissner's membrane; those with mild hydrops show displacement of Reissner's membrane but the area of the endolymphatic space does not exceed the area of the scala vestibuli; and in those with significant hydrops the area of the endolymphatic space exceeds the area of the scala vestibuli.

A primary cause of deafness is damage of receptor cells in the inner ear. Clinically, it has been demonstrated that effective functionality can be provided by electrical stimulation of the auditory nerve, thus bypassing damaged receptor cells. However, subsequent to sensory cell loss there is a secondary degeneration of the afferent nerve fibers, resulting in reduced effectiveness of such cochlear prostheses. The effects of neurotrophic factors were tested in a guinea pig cochlear prosthesis model. After chemical deafening to mimic the clinical situation, the neurotrophic factors brain-derived neurotrophic factor and an analogue of ciliary neurotrophic factor were infused directly into the cochlea of the inner ear for 26 days by using an osmotic pump system. An electrode introduced into the cochlea was used to elicit auditory responses just as in patients implanted with cochlear prostheses. Intervention with brainderived neurotrophic factor and the ciliary neurotrophic factor analogue not only increased the survival of auditory spiral ganglion neurons, but significantly enhanced the functional responsiveness of the auditory system as measured by using electrically evoked auditory brainstem responses. This demonstration that neurotrophin intervention enhances threshold sensitivity within the auditory system will have great clinical importance for the treatment of deaf patients with cochlear prostheses. The findings have direct implications for the enhancement of responsiveness in deafferented peripheral nerves. Hearing impairment is the most frequent disability of people in industrialized countries, affecting more than one in seven individuals. Most hearing loss is caused by destruction of the sensory cells within the cochlea of the inner ear. In mammals, the auditory cells do not regenerate, nor are there currently effective interventions for their repair. Moreover, in the auditory system, as in other afferent systems, degeneration of the auditory nerve occurs secondary to the loss of the inner ear sensory cells (hair cells), thus aggravating the functional impairment. In the severely and profoundly deaf, the cochlear implant (prosthesis) has been shown to provide an effective habilitative intervention. The cochlear prosthesis consists of one or more electrodes inserted into the fluid space of the inner ear. The implant operates by directly electrically stimulating the auditory nerve, bypassing damaged or missing sensory receptor cells. This device now provides significant speech understanding, with a score for everyday sentence understanding of about 80% without lip reading in the majority of patients implanted (so far more than 40,000 worldwide) (1-3). However, the cochlear prosthesis depends on remaining excitable auditory nerve fibers, and their loss severely compromises the effectiveness of the implant and the hearing benefits it provides. Studies show a clear relationship between the total number of viable auditory neurons available for stimulation and the performance of subjects receiving cochlear implant...

Age-related hearing impairment (ARHI), or presbycusis, is the most prevalent sensory impairment in the elderly. ARHI is a complex disease caused by an interaction between environmental and genetic factors. Here we describe the results of the first whole genome association study for ARHI. The study was performed using 846 cases and 846 controls selected from 3434 individuals collected by eight centers in six European countries. DNA pools for cases and controls were allelotyped on the Affymetrix 500K GeneChip for each center separately. The 252 top-ranked single nucleotide polymorphisms (SNPs) identified in a non-Finnish European sample group (1332 samples) and the 177 top-ranked SNPs from a Finnish sample group (360 samples) were confirmed using individual genotyping. Subsequently, the 23 most interesting SNPs were individually genotyped in an independent European replication group (138 samples). This resulted in the identification of a highly significant and replicated SNP located in GRM7, the gene encoding metabotropic glutamate receptor type 7. Also in the Finnish sample group, two GRM7 SNPs were significant, albeit in a different region of the gene. As the Finnish are genetically distinct from the rest of the European population, this may be due to allelic heterogeneity. We performed histochemical studies in human and mouse and showed that mGluR7 is expressed in hair cells and in spiral ganglion cells of the inner ear. Together these data indicate that common alleles of GRM7 contribute to an individual's risk of developing ARHI, possibly through a mechanism of altered susceptibility to glutamate excitotoxicity.

People with poor hearing acuity have a higher risk for falls, which is partially explained by their poorer postural control. Auditory information about environment may be important for safe mobility.

Meniere's disease (MD) is a disorder of the inner ear that causes vertigo attacks, fluctuating hearing loss, tinnitus and aural fullness. The aetiology of MD is multifactorial. A characteristic sign of MD is endolymphatic hydrops (EH), a disorder in which excessive endolymph accumulates in the inner ear and causes damage to the ganglion cells. In most patients, the clinical symptoms of MD present after considerable accumulation of endolymph has occurred. However, some patients develop symptoms in the early stages of EH. The reason for the variability in the symptomatology is unknown and the relationship between EH and the clinical symptoms of MD requires further study. The diagnosis of MD is based on clinical symptoms but can be complemented with functional inner ear tests, including audiometry, vestibular-evoked myogenic potential testing, caloric testing, electrocochleography or head impulse tests. MRI has been optimized to directly visualize EH in the cochlea, vestibule and semicircular canals, and its use is shifting from the research setting to the clinic. The management of MD is mainly aimed at the relief of acute attacks of vertigo and the prevention of recurrent attacks. Therapeutic options are based on empirical evidence and include the management of risk factors and a conservative approach as the first line of treatment. When medical treatment is unable to suppress vertigo attacks, intratympanic gentamicin therapy or endolymphatic sac decompression surgery is usually considered. This Primer covers the pathophysiology, symptomatology, diagnosis, management, quality of life and prevention of MD.

ObjectivesTo evaluate the onset of vertigo, hearing loss and tinnitus in Ménière's disease and the associated endolymphatic hydrops (EH) of the inner ear.DesignMulticentre evaluation of three patient groups.SettingsDisease-specific symptoms were reviewed among referred patients in a tertiary referral hospital in Finland and in members of a Finnish Ménière Association in Finland. The MRI of a separate group of patients was undertaken in a tertiary referral centre in Japan.Participants340 patients were reviewed in the referral hospital along with 740 members of the Ménière Association. MRI was undertaken in 224 patients in Japan.Primary and secondary outcome measuresLatency and symptom development in Ménière's disease, and the appearance of EH of the inner ear in monosymptomatic patients and in Ménière's disease.ResultsThe mean age of the first symptom was 43.8 years, with 10% of the patients being older than 65 years. The time delay between hearing loss and vertigo was more than 5 years in 20% of the members and of the patients. Gadolinium-contrasted MRI demonstrated EH in 90% of the patients with Ménière's disease, in which 75% was bilateral among patients with unilateral symptoms. In monosymptomatic patients with vertigo, tinnitus or hearing loss; EH was demonstrated in 55–90% of the patients either in the cochlea and/or the vestibulum of the symptomatic ear.ConclusionsMénière's disease often shows bilateral EH and comprises a continuum from a monosymptomatic disease to the typical symptom complex of the disease. We suggest that a 3T MRI measurement should be carried out in patients with sensory-neural hearing loss, vertigo and tinnitus, 4 h after the intravenous injection of a gadolinium-contrast agent to verify the inner ear pathology. This may lead to a better management of the condition.

We quantified the effect of vision, pressoreceptor function and proprioception on the postural stability at different ages. Altogether 212 healthy volunteers (ages from 6 to 90 years) were examined by using a computerised force platform. The sway velocity (SV) was measured with eyes open and eyes closed during quiet stance on a bare platform and a foam plastic covered surface. In addition, to study the proprioceptive system, pseudorandom vibration perturbation was applied on the calf muscles. The SV showed a U-shaped curve: the children and the oldest swayed most. Equilibrium was most stable around 50 years. The visual system was of most importance for balance control in the old. The children were sensitive of pressoreceptor and proprioceptive perturbation, indicating the importance of these systems for their postural control.