Presbycusis

Presbycusis (also spelt presbyacusis, from Greek presbys “elder” + akousis “hearing”^[1]), or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive bilateral symmetrical age-related sensorineural hearing loss. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of multiple causes of hearing loss can be difficult.

Presentation

Deterioration in hearing has been found to start very early, from about the age of 18 years. The ISO standard 7029 shows expected threshold changes due purely to age for carefully screened populations (i.e. excluding those with ear disease, noise exposure etc.), based on a meta-analysis of published data.^[2][3] Age affects high frequencies more than low, and men more frequently than women. One early consequence is that even young adults may lose the ability to hear very high frequency tones above 15 or 16 kHz. Despite this, age-related hearing loss may only become noticeable later in life. The effects of age can be exacerbated by exposure to environmental noise, whether at work or in leisure time (shooting, music, etc.). This is noise-induced hearing loss (NIHL) and is distinct from presbycusis.

Over time, the detection of high-pitched sounds becomes more difficult, and speech perception is affected, particularly of sibilants and fricatives. Both ears tend to be affected.

Pathophysiology

Examples of microscopic changes seen in this condition are hair cell degeneration of the cochlea and giant stereociliary degeneration.

Causes

Factors that can cause hearing loss, which can be difficult to distinguish or separate from presbycusis, include:

• Heredity: Features like early aging of the cochlea and susceptibility of the cochlea for drug insults are genetically determined.
• Atherosclerosis: May diminish vascularity of the cochlea, thereby reducing its oxygen supply.
• Dietary habits: Increased intake of saturated fat may accelerate atherosclerotic changes in old age.
• Diabetes: May cause vasculitis and endothelial proliferation in the blood vessels of the cochlea, thereby reducing its blood supply.
• Noise trauma: Exposure to loud noise/music on a continuing basis stresses the already hypoxic cochlea, hastening the presbycusis.
• Smoking: Is postulated to accentuate atherosclerotic changes in blood vessels aggravating presbycusis.
• Hypertension: Causes potent vascular changes, like reduction in blood supply to the cochlea, thereby aggravating presbycusis.
• Ototoxic drugs: Ingestion of ototoxic drugs like aspirin may hasten the process of presbycusis.

Treatments In Progress

Devices like hearing aids and cochlear implants already help improve hearing of many elderly. Though still in their early stages, several treatments for presbycusis are in development. Included in these are the water-soluble coenzyme Q10 formulation, fetal thymus grafting, and the prescription drug Tanakan. In a study performed in 2010, it was found that the water-soluble formulation of coenzyme Q10 (CoQ10) caused a significant improvement in liminar tonal audiometry of the air and bone thresholds at 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz.^[4] It is likely that a larger clinical trial will be performed in order to gain more supporting evidence for the effects of CoQ10 in averting the development of hearing loss for people suffering from presbycusis. A fetal thymus graft, or rejuvenation of the recipient immunity by inoculation of young CD4+ T cells, also prevents presbycusis as well as up-regulation of the interleukin 1 receptor type II gene (IL1R2) in CD4+ T cells and degeneration of the spiral ganglion in Samp1 mice, a murine model of human senescence.^[5] The effects of the pharmaceutical drug Tanakan were observed when treating tympanophonia in elderly women.^[6] Tanakan was found to decrease the intensity of tympanitis and improve speech and hearing in aged patients, giving rise to the idea of recommending treatment of it to elderly patients with presbycusis or normal tonal hearing.^[6]

Cultural aspects

Recently, the ability of young people to hear high frequency tones that are inaudible to others over 25 or so has led to the development of technologies to disperse groups of yobboes around nearby British shops (The Mosquito), and the development of a cell phone ringtone, Teen Buzz, for students to use in school, that many older instructors are unable to hear. In September 2006 this technique was used to make a dance track called 'Buzzin'.^[7] The track had two melodies, one that everyone could hear and one that only younger people could hear.

See also

• Hearing range
• Absolute threshold of hearing
• The Mosquito
• Presbyopia

References