Aging after Noise: Biomarkers, Clinical Assessment, and Pharmacotherapy of Hidden Noise Injury
Abstract
Noise-induced hearing loss results when exposure to damaging levels of sound injures delicate inner ear structures and compromises vulnerable inner ear functions. The noise-induced sensitivity loss captured by the clinical audiogram can be temporary or permanent, and the underlying injury can be subtle or dramatic. Permanent threshold sensitivity losses after noise are associated with permanent cochlear injury, often sensory hair cell loss or damage. These consequences of noise are the focus of regulations designed to protect against noise injury, they are the focus of clinical diagnosis and treatment, for example, with hearing aids, and they are the ongoing focus of drug therapies aimed at protection and repair. Recent work in our laboratory has shown, however, that noise exposure has insidious consequences that continue to change the ways that ears and hearing age, long after the noise has stopped. Noise interrupts communication between sensory hair cells and cochlear nerve fibers within hours and produces widespread cochlear nerve loss over months to years. This can occur even when the exposure produced only temporary changes in hearing thresholds and caused no loss of hair cells. This neurodegeneration permanently changes the way sound information is processed. It may contribute to difficulties hearing out signals like speech in a background of noise and to a variety of abnormal auditory perceptions like tinnitus and hyperacusis, which are commonly reported by individuals who have been exposed to loud noise. Our discovery of these ongoing neurodegenerative changes after noise has important implications for military personnel, who are at high risk for such exposure. At present, clinical assessment methods in primary use are largely silent to their presence and current drug therapies do not target these consequences. Ultimately, the diagnosis and management of noise-induced injury, including its pharmacologic treatment, should proceed in ways consistent with our improved understanding of underlying processes and pathology. We have three major goals with this research. First, we wish to better understand how noise exposures, particularly those from which the ear appears to recover, result in progressive nerve loss. Second, we aim to uncover mechanisms associated with the initial, instigating events and the processes that are subsequently set into play by the exposure; this will provide important information to efforts aimed at targeting these mechanisms for prevention or repair. Finally, there is the practical matter of diagnosing this "hidden" injury, which does not reveal itself in the standard clinical threshold sensitivity tests commonly used to assess the magnitude of noise-induced injury. Here, we will refine assessments so that they are more sensitive to the underlying neurodegeneration. Normal hearing function depends on more than normal thresholds. It is clear that difficulty hearing in noisy backgrounds is a very common complaint; often, speech can be "heard," but not understood. Although this difficulty is exaggerated by threshold sensitivity loss, the complaint is fairly universal as individuals age, even before there is significant threshold loss. We believe that this kind of noise-induced neurodegeneration may be a common contributor. Work proposed here will lead to improved understanding of the functional consequences of this neural loss and to improved clinical diagnosis and treatment for military personnel with noise-induced cochlear injury. By "exploring innovative approaches to protect, support, and advance the health and welfare of military personnel," and "by accelerating translation of advances in knowledge into evaluation and treatment strategies that could be applied in theater or in clinical facilities of the Military Health System," this proposal directly addresses healthcare needs of military personnel.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 29, 2016
- Source ID
- W81XWH1510103
Entities
People
- Sharon Kujawa
Organizations
- Massachusetts Eye and Ear Infirmary
- United States Army