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There are two kinds of deafness. One is due to wax and is curable; the other is not due to wax and is not curable.
SIR WILLIAM WILDE (1815–76)
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Deafness is defined as impairment of hearing, regardless of its severity.1 It is a major community health problem requiring a high index of suspicion for diagnosis, especially in children. Deafness may be conductive, sensorineural or a combination of both (mixed).
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Key facts and checkpoints
Deafness occurs at all ages but is more common in the elderly (see FIG. 43.1). Fifty per cent of people over 80 years have deafness severe enough to be helped by a hearing aid.
The threshold of normal hearing is from 0–20 decibels (dB), about the loudness of a soft whisper.
One in seven of the adult population suffers from some degree of significant hearing impairment (over 20 dB in the better-hearing ear).2
One child in every 1000 is born with a significant hearing loss. The earlier it is detected and treated the better.
Degrees of hearing impairment with vocal equivalent:2,3
– mild = loss of 20–40 dB (soft-spoken voice is 20dB)
– moderate = loss of 40–60 dB (normal-spoken voice is 40dB)
– severe = loss of 70–90 dB (loud spoken voice)
– profound = loss of over 90 dB (shout is 90–120dB)
More women than men have a hearing loss.
People who have worked with high noise levels (>85 dB) are more than twice as likely to be deaf.
There is a related incidence of tinnitus with deafness.
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It is useful to consider the causes of deafness in terms of pathophysiology (conductive or sensorineural hearing loss) and anatomical sites (see FIG. 43.2).
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Conductive hearing loss is caused by an abnormality in the pathway conducting sound waves from the outer ear to the inner ear,1 as far as the footplate of the stapes.
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Sensorineural hearing loss (SNHL) is a defect central to the oval window involving the cochlea (sensor), cochlear nerve (neural) or, more rarely, central neural pathways.1
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Congenital deafness is an important consideration in children, while presbyacusis is very common in the aged. The commonest acquired causes of deafness are impacted cerumen (wax), serous otitis media and otitis externa. Noise-induced deafness is also a common problem.
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It is important not to misdiagnose an acoustic neuroma, which can present as acute deafness, although slow progressive loss is more typical. A summary of the diagnostic strategy model, which includes several important causes ...