Hidden age-related hearing loss and hearing disorders: current knowledge and future directions

Age-related hearing loss, which affects roughly 35% of those over the age of 70, is the second most common disorder among the elderly. The severity of age-related hearing loss may actually be worse if assessments are made under more realistic conditions, such as communicating in noise. Emerging data from humans and animal models suggest that damage to the inner hair cells and/ or type I neurons that relay sound information to the brain may contribute to hearing deficits in a noisy background. Data obtained from carboplatin-treated chinchillas suggest that tone-in-noise thresholds are a sensitive and frequency dependent method of detecting damage to the IHC/type I system. Therefore, tone detection thresholds measured in broadband noise may provide an efficient method of detecting the deficits in specific frequency regions. Preliminary data obtained in elderly subject with normal thresholds in quiet compared to young subjects illustrate the importance of repeating these measurements in broadband noise because thresholds in noise were worse for our elderly subjects than young subjects, even though both groups had similar hearing thresholds in quiet. N-acetyl cysteine supplementation which protects against inner hair cell loss in animal models may represent a viable therapy for protecting the inner hair cell/type I neurons.