Hearing loss in the ageing patient is common. In recent Australian surveys, 26.6% of the population have some hearing impairment, while in the 70+ age group this prevalence rises to 87.5%.
Deterioration of hearing with increasing age is not inevitable. As a case in point, the Mabaan people of Sudan are known to maintain a healthy diet, exercising daily, avoiding tobacco smoke and noisy environments; most of this population maintain their hearing in the normal range well into old age. The normal processes of ageing affect all subsections of the ear, but it is the effects on the inner ear and the resultant sensorineural hearing loss that causes elderly patients the most morbidity.
Presbycusis is the term used to describe sensorineural hearing loss secondary to the ageing process and is presumed to be the result of multiple, repeated insults to a patient’s cochlear function. Presbycusis is both a diagnosis of exclusion and an umbrella term for multiple presumed pathological processes. Damage to the cochlea occurs due to the age-related accumulation of genetic damage and gradual decline in the numbers of neural and supporting cells within the cochlea. Other possible causes of cochlear damage include:
- Repeated exposure to ototoxic medications
- Vascular pathology
- Inflammation from nearby middleear disease
The higher incidence and greater severity of presbycusis in men is hought to be largely due to the differences in noise exposure experienced by men and women in occupational and recreational activities.
Cell population decline has been observed at all locations along the auditory pathway. Central changes leading to difficulty with hearing can be classified as primary or secondary. Primary changes include reduced volume of brain tissue involved in auditory processing. Lipofuscin accumulation has also been noted in ageing central auditory neurons, as it has in ageing tissues elsewhere in the body. This senescent change is in addition to other pathologies common in the elderly that affect brain health, such as arteriosclerosis or respiratory failure. Overall, these hearing-related changes are referred to as central effects of biological ageing and have been found to cause difficulty in judging the duration of sounds, perceiving gaps in sounds and localising sounds in space. Secondary brain changes occur in situations of auditory deprivation from hearing loss due to pathology anywhere in the ear. Hearing-loss induced neuroplasticity, or central effects of peripheral pathology, can increase the sensitivity (decreased decibel threshold) of the deprived central auditory neurons, typically at the expense of frequency and temporal resolution. There is, however, evidence for beneficial neuroplasticity when auditory input is restored, such as with ‘aiding’ of a previously unaided ear (ie, use of a hearing aid or implanted device).