Pathophysiology of Age-Related Hearing Loss (Peripheral and Central)

Abstract

Age-related hearing loss (presbycusis) refers to bilaterally symmetrical hearing loss resulting from aging process. Presbycusis is a complex phenomenon characterized by audiometric threshold shift, deterioration in speech-understanding and speech-perception difficulties in noisy environments. Factors contributing to presbycusis include mitochondria DNA mutation, genetic disorders including Ahl, hypertension, diabetes, metabolic disease and other systemic diseases in the intrinsic aspects. Extrinsic factors include noise, ototoxic medication and diet. However, presbycusis may not be related to the intrinsic and extrinsic factors separately. Presbycusis affects not only the physical, cognitive and emotional activities of patients, but also their social functioning. As a result, patients' quality of life deteriorates, compounded by various symptoms including depression, social isolation and lower self-esteem. Presbycusis is classified into six categories, as based on results of audiometric tests and temporal bone pathology, established by Schuknecht (1993): sensory, neural, metabolic or strial, cochlear conductive, mixed and indeterminate types. Among these, metabolic presbycusis is the mainstay of presbycusis types. Age-related changes also develop in the central hearing system. Functional decline of the central auditory system, caused by aging, reduces speech-understanding in noisy background and increase temporal processing deficits in gap-detection measures. This study reviews the literature on the age-related hearing loss.

Hypertension is associated with dysfunction of both peripheral and central auditory system

“…T he negative influence of hypertension on the peripheral, cochlear part of the hearing system is well documented [1][2][3][4][5][6][7][8][9]. However, little is known about the central auditory function in patients with hypertension.…”

Hearing impairments, presbycusis and the possible therapeutic interventions

“…The mtDNA mutation in mice showed early presbycusis (Niu et al, 2007). In human mtDNA 4977 mutation related to presbycusis and mtDNA 4834 in rodents (Lee, 2013).…”

“…In these models, inside the gerbils, a decline of endocochlear potential, the atrophy of spinal ligaments and stria vascularis were investigated (Gratton et al, 1997;Mills et al, 1990). Similar to humans, Chinchillas have aged-related hearing loss, but poses a limitation as it has long life span of 20 years, therefore does not use for the studies of presbycusis (Lee, 2013).…”

No longer falling on deaf ears: Mechanisms of degeneration and regeneration of cochlear ribbon synapses

“…Both types of hearing loss are associated with multiple risk factors, including genetic predispositions, poor diet and chronic diseases such as diabetes and hypertension (Daniel, 2007; Lee, 2013). Degeneration of hair cells and sensory neurons were thought to be the cause of these disorders (Liberman et al, 1984; Robertson, 1982).…”