Clinical measures of auditory function: The cochlea and beyond

Abstract

Hearing loss is one of the world’s leading chronic health conditions and becomes increasingly prevalent in older adults, exceeding 90% in individuals over 80 years old.1–3 For many, it results in psychosocial consequences including depression and social isolation.4–6 Decreases in health-related quality of life have also been reported,7 and although it is not thought of as a life-threatening health condition, hearing loss causes communication interference that can substantially affect social integration, functional ability, and self-image. Furthermore, it may impede safety by limiting an individual’s ability to hear warning signals and sirens (e.g., in agricultural settings8). Noise-induced hearing loss further poses a significant public health problem, as approximately 10% of U.S. adults (22 million) between 20–69 years old have permanent hearing loss due to exposure to loud noise at work or during leisure activities.9 Research conducted over the last two decades has brought attention to the ototoxic effects of medications and chemicals and their potentially synergistic effects with noise.10–13 In some occupational settings such as refinery, paint industry, aviation industry, military, and fire service, it is common to encounter exposure to both noise and ototoxic chemicals,14 making early detection and intervention critical. Please refer to companion papers exploring noise induced hearing loss by Hong and colleagues as well as ototoxicity by Campo and colleagues. A growing number of factors associated with increased risk of hearing loss in adulthood include: gender,15 genetic susceptibility,16 racial/ethnic groups,17,18 and other diseases such as risk factors associated with cardiovascular disease (e.g., history of hypercholesterolemia, diet, and smoking).19–22 Diabetes (both Types I and II) has been associated with prevalent hearing loss.23,24 Evaluation of hearing loss associated with the combined effects of these risk factors requires tests that can fully evaluate the auditory system, from the cochlea to the higher auditory centers; however, there is no “gold standard” audiological test protocol available for this purpose at this time. The objective of this review is to discuss the tools commonly used in the clinic and present emerging strategies to aid in the early identification of hearing loss in adults. Audiological evaluation of pediatric populations requires a unique set of considerations that are beyond the scope of this paper (for review and pediatric evaluation recommendations, see Harlor et al., 200925). Hearing loss continues to be a chronic disease that significantly impacts quality of life and work productivity, especially for workers who labor in noisy environments.26 The disease also places a significant financial burden on society, as it is estimated the lifetime cost of severe to profound hearing loss exceeds $250,000 per patient in the U.S.27 mostly due to losses in work productivity. Increased awareness and understanding of hearing loss identification and prevention will help mitigate the detrimental consequences of hearing impairment on individuals and society. This paper will provide a basic appreciation of hearing loss assessment needed for this promotion and advancement in hearing health.