This article is mainly intedend for use by medical professionals.
Presbycusis, or age associated hearing loss, is a common cause of hearing loss in adults. The condition has very bad impact on the quality of life of millions of elderly people.
Age associated hearing loss is defined as a mid to late adult onset, bilaterally symmetrical and progressive sensory neural hearing loss, where other underlying causes have been excluded.
Studies have even shown that age related hearing loss has direct connection with early onset dementia and Alzheimer’s disease.
Epidemiology
Auditory acuity is best at teen ages and in early twenties. From there on, there is progressive decline in hearing acuity, the rate is higher in men and manual laborers.
Age associated hearing loss is an almost inevitable clinical condition. The condition is more severe in males than females, possibly related to higher levels of noise exposure seen among males.
It occurs from 6th decade of life onwards. The rate of hearing loss accelerates with time; so, the older the patient is, the greater the hearing loss expected.
Above 50 years, the prevalence of hearing impairment (>30dB) is 17%. Above 60 years the reported prevalence of hearing loss is 30% and above 70 years this is above 53%. Most adults over the age of 80, and nearly all adults who are 90 or older are suffering from age related hearing loss.
The World Health Organization (WHO) estimates that by 2025 there will be 1.2 billion people over 60 years of age worldwide, with more than 500 million individuals who will suffer significant impairment from presbycusis.
Risk factors for Age associated hearing loss.
Risk factors for presbycusis can be broadly divided into two – Genetic and Environmental.
Though genetic factors are important in Age associated hearing loss, the genetics of this clinical condition is poorly defined. No associated genes or loci have been identified so far.
Genetic studies in mouse have pointed to ahl gene which maps to chromosome 10. This is inherited in a recessive pattern. The gene is orthologues to cadherin 23 – human deafness gene associated with non-syndromic hearing loss and usher syndrome. Other loci detected are ahl2 in chromosome 5 and ahl3. It is also suggested that mitochondrial genome mutations or variation, either inherited or acquired may contribute to age related hearing loss.
Exact role of environmental factors is not known. Noise exposure, smoking, ototoxic drugs, alcohol use, ear infections, diabetes mellitus, vascular disease, immunologic disorders, hypertension, diabetes, and hormonal factors (eg, aldosterone, thyroid hormones, estrogen) and hyper viscosity may exacerbate presbycusis.
Pathology
Human ear has got three parts, external, middle and inner ear. Diseases involving any of these parts of the ear can cause hearing loss.
- External ear
- Increased cerumen production
- Reduced epithelial migration.
- Increased hair growth in the external auditory canal
- Potential collapse of external auditory canal
- Enlargement of pinna.
- Middle ear
- Stiffening, thinning, loss of vascularity of tympanic membrane.
- Arthritic changes and ossification in ossicles and ossicular changes.
- Degeneration of middle ear muscles.
- Calcification of cartilaginous support of eustachian tube.
- Inner ear
- Schuknecht has defined 6 hypothetical histopathological types of inner ear pathology for age related hearing loss.
- Sensory type
- Loss of hair cells (and of sustentacular cells) at the basal end of organ of corti.
- Characterized by high frequency hearing loss and poor speech discrimination.
- Neural type
- There is degeneration of neurons of cochlear nerve, with resulting cochlear ganglion cell loss.
- Believed to be the most common type.
- Characterized by high frequency hearing loss.
- Poor speech discrimination which is out of proportion to pure tone audiometry loss
- Vascular / Metabolic / Strial type
- Involves atrophy of stria vascularis with associated loss of strial tissue primarily I apical and middle turns of cochlea.
- Characterized by flat audiogram with good speech discrimination score.
- Mechanical or cochlear conductive
- Due to increased stiffness of basilar membrane – due to increase in number of fibrillar layer of basilar membrane.
- Characterized by gradually descending (approximately 25dB/octave) pure tone audiometry
- Intermediate type
- Change in characteristics of cochlear duct at submicroscopic levels.
- These changes are seen in intracellular organelles involved in cell metabolism, decrease in synapse numbers and changes in endolymph composition.
- Mixed
- Involving some combination of other five.
- Central pathology
- Age related changes in central nervous system – reduced neural plasticity.
Diagnosis
Diagnosis of presbycusis in an individual over 60 years of age, with normal ear examination findings and a symmetrical, often predominantly high tone hearing loss is fairly secure.
High tone hearing loss above 50 years age is mostly age associated hearing loss, in the absence of any alternative explanation. Under the age of 50, an alternative diagnosis should be made.
Patient history: The diagnosis of age associated hearing loss is made on clinical grounds, on basis of recognizable features in patients’ history. These include.
- The history of slow and insidious hearing problem.
- Often first symptom is difficulty in hearing conversation particularly in background noise – referred as the “cocktail party effect”.
- Patient describes a lack of clarity rather than decrease in volume.
- Patient frequently ask others to repeat themselves.
- Keeps the volume of TV louder than is comfortable for other members of household.
- Sometimes tinnitus (ringing in the ear) may be the presenting feature (in 30-50% patient)
- Paradoxical hypersensitivity to loud sounds – sounds become too loud at levels that would easily be tolerated by persons with normal hearing
- Social isolation and depression
- Positive family history
- Hearing loss can also be accompanied by vertigo, and disequilibrium (presbyastasis) leading to falls.
Before making a diagnosis of presbycusis, other clinical conditions mimicking a diagnosis of the same should be ruled out. These include head injury, meningitis, serious systemic illness, previous ototoxic drug therapy (aminoglycoside, platinum derivatives, loop diuretics and salicylates), Meniere’s, strong family history of early hearing loss (indicate non-syndromic genetic/ hereditary degenerative hearing loss) etc.
On clinical examination: it will be an elderly patient, usually in fifties. Ear examination will be typically normal.
Investigations for age associated hearing loss.
There exists no specific test for diagnosis of presbycusis.
Audiogram will be showing a typically symmetrical hearing loss, worsening at higher frequencies (above 2KHz). As condition worsens, there will be progressive loss of middle (1-2KHz) and even low (250-500Hz) frequencies.
Imaging studies, including magnetic resonance imaging (MRI) and computed tomography (CT), are usually not needed for the diagnosis of presbycusis. In case of asymmetric hearing loss, MRI needs to be done to rule out retro-cochlear pathologies. A difference of more than 10dB averaged over frequencies 0.5, 1, 2, 4KHz or 20dB or more at any single frequency is a reasonable indication for advising MRI. MRI is also advisable in case of patients with unilateral tinnitus.
Treatment of presbycusis
Psychological counselling will help the patient understand the clinical condition and their limitations. Specific treatment options include,
Hearing aids – There is some emerging evidence in a recent meta-analysis and systematic review (Yeo et al, 2022); researchers found that hearing aid users had lower hazards of cognitive decline relative to non-users as well as a three percent improvement in cognitive test scores after the use of hearing aids.
Hearing aid trials are recommended when high-frequency thresholds are greater than 40 dB on the audiogram. Binaural (bilateral) heading aids are ideal for presbycusis. They help in improving the quality of life by improving social withdrawal, depression, and emotional impact which are commonly associated with presbycusis.
Those individuals with mild – high tone hearing loss will have little benefit with hearing aids. Unfavorable experiences with hearing aid can be avoided through careful testing, counseling, device selection, and fitting by an experienced audiologist.
Well fit hearing aid can ameliorate tinnitus in some patients. Tinnitus retraining therapy, cognitive, directive counselling and sound therapy can provide 60-70% success rates.
Cochlear implants – Studies have shown that, where hearing aids no longer provide benefit, cochlear implantation is the treatment of choice with excellent results. But the improvement in hearing may be limited by the age-related reduction in ability to process sound information, as well as age-related cognitive deficits.
Advice regarding optimization of acoustic environment – e.g.: reduction of background noise, face to face conversation and an explanation of problem to allow legitimization of hearing loss should be given to the patient and the care takers.
Use of assistive devices like – Infrared headphones for TV, volume controllable telephones, Louder doorbells with an alternative system like flashing light or vibrations can reduce the impact of presbycusis on daily life. Assistive devices are usually employed in addition to hearing aid.
Auditory rehabilitation: includes interventions such as active listening training, education on reading facial expressions or lip contours of speakers etc. These are usually practiced in combination with hearing devices.
References
- Gates GA, Mills JH. Presbycusis. The lancet. 2005 Sep 24;366(9491):1111-20.
- Wattamwar K, Qian ZJ, Otter J, et al. Increases in the Rate of Age-Related Hearing Loss in the Older Old. JAMA Otolaryngol Head Neck Surg 2017; 143:41.
- Rutherford BR, Brewster K, Golub JS, et al. Sensation and Psychiatry: Linking Age-Related Hearing Loss to Late-Life Depression and Cognitive Decline. Am J Psychiatry 2018; 175:215.
- Griffiths TD, Lad M, Kumar S, Holmes E, McMurray B, Maguire EA, Billig AJ, Sedley W. How can hearing loss cause dementia?. Neuron. 2020 Nov 11;108(3):401-12.
- Yeo BSY, Song HJJM, Toh EMS, et al. (2022) Association of hearing aids and cochlear implants with cognitive decline and dementia: a systematic review and meta-analysis. JAMA Neurol. In press.