Acute Hearing Loss
Acute hearing loss falls into two broad categories: noise induced and drug-induced.
Noise induced hearing loss
Noise induced hearing loss makes up 9% of all types of hearing loss in developed world, and affects around 1.35% of total population.
In the developed world, occupational exposure is decreasing due to improved hearing protection. In the US, it has been estimated that over 20 million people are exposed to high levels of occupational noise, in industries such as construction, mining, agriculture and others. In the developing world it is likely that ear protection is less frequently used and so hearing damage will continue at high rates.
Social exposure to noise is increasing throughout the world through personal music players, night clubs and rock concerts. It is unclear to what extent exposure through personal headphones will affect hearing in later life, depending on the length and volume of exposure. However, research has started in this area. Also, for example, 72% of teenagers experienced reduced hearing ability after attending a rock concert.
Hearing disorders and hearing loss in the military are common: hearing damage is the leading disability in the war on terror, according to the Department of Veterans Affairs.
Acute or long term exposure to noise leads to damage to the cochlea and loss of hair cells. This in turn leads to adaptive changes in the central nervous system that further exacerbates the problem and can lead to tinnitus. Research conducted by Dr Martine Hamann at the University of Leicester in collaboration with Autifony has shown that key cells (neurons) in the auditory brainstem fire erratically following exposure to loud noises.
Drug induced hearing loss (ototoxicity)
Over 130 approved drugs can cause ototoxicity through direct effect on cochlear biology. There are three main categories of ototoxic drugs:
- Platinum based anti-cancer drugs
- Aminoglycoside antibiotics
- Loop diuretics, primarily used to treat hypertension and oedema
Cancer patients are at greatest risk as they may be prescribed more than one of these groups.
In this case, damage to the cochlea is the direct result of chemical injury to the delicate hair cells and mechanisms that sustain the function of the organ. However, downstream central pathology is likely to be similar to that occurring following noise damage.