2 Age-Associated Hearing Loss

As with all sensory systems in the human body, there is a progressive degeneration in the auditory system with ageing. Presbyacusis is the term that describes the deterioration of hearing that characterises old age, now replaced by the term ‘age-associated hearing loss’ (AAHL). It may be defined as a progressive bilateral sensorineural hearing loss of mid-to-late adult life, where all other causes have been excluded. Indeed, the definition of AAHL is somewhat arbitrary; there is no agreed age above which an individual suffers from age-related hearing loss and below which one does not. Almost invariably, databases displaying age-related, average hearing thresholds for either screened or unscreened populations show a marked increase in the rate of progression of the hearing loss once into the sixth decade. It is, therefore, reasonable to attribute high-tone hearing loss in an individual over the age of 50 to age-related changes (in the absence of any alternative explanation).

2.1 Pathophysiology

Both the sensory peripheral (cochlea) and central (neural) components of the auditory system are affected and the deterioration appears to become more rapid with increasing age. Peripheral degeneration is reported to be responsible for at least two-thirds of the clinical features of presbyacusis. A variety of possible mechanisms exist. Cellular degeneration gives rise to a reduction in the numbers of inner and outer hair cells, particularly at the basal end of the cochlea. This can lead to secondary neural degeneration in the spiral ganglion. Circulatory changes such as arteriosclerosis, atrophy of the stria vascularis and microangiopathy can lead to metabolic upset and further cell death. This leads to an elevation of hearing thresholds and a loss of frequency selectivity. Degeneration in the central pathways leads to a reduction in performance in terms of signal processing. The net result in most instances will be a combined sensorineural, rather than an isolated sensory or neural impairment.

2.2 Clinical Features

Moderate hearing impairment (45-dB hearing level averaged over 0.5, 1, 2 and 4 kHz) occurs in 4% of the 51 to 60 age group, and in 18% of those aged 71 to 80. Men and women are both affected, although men tend to have a slightly worse loss for the same age group.

Initially, patients will complain of difficulty in hearing, particularly in the presence of background noise, so that they find conversations difficult to follow. As the hearing loss progresses, they will become aware of not hearing words and sounds. Recruitment is a frequent problem and adds to the distortion. In addition, the problems and consequences of AAHL are compounded in the elderly because of additional degenerative processes in the central nervous system. This can result in a relative loss in neuronal plasticity, a loss of cognitive abilities and other sensory modalities, particularly sight.

Stay updated, free articles. Join our Telegram channel

Join