Causes of deafness
- © CBM
There are many causes of deafness, and some people are deaf from birth while others progressively lose their hearing as they get older.
Congenital deafness describes loss of hearing that is already present at birth.
This may be due to inherited causes:
- Deafness can run in the family.
- Deafness can be part of a genetic disease (e.g. Waardenburg syndrome).
- Deafness can accompany abnormal physical traits (e.g. ear malformation).
In addition, certain other factors can influence hearing development:
- Certain drugs (ototoxic drugs), taken by the expectant mother, can damage the hearing of the unborn child.
- Infections of the expectant mother: Mainly rubella, cytomegalovirus, and syphilis. Toxoplasmosis is a less common cause than previously thought.
- Difficulties during or soon after birth: premature birth, lack of oxygen, head trauma, jaundice.
Congenital deafness is usually irreversible. The effects of congenital deafness or hearing impairment can often be ameliorated by use of amplification devices including hearing aids and cochlear implants together with rehabilitation and education.
But a number of preventive measures can reduce the risk:
- Rubella vaccination, screening and treatment for syphilis.
- Good antenatal care and supervised births.
- Raised awareness amongst professionals and parents about the risks of potentially ototoxic medications.
- Congenital syphilis can be treated with high dose penicillin, but is best prevented by identification and eradication of the infection in the mother.
Otitis media (middle ear infection) means ear infections with inflammation in the middle ear area. Otitis media can be caused by either bacteria or viruses and occurs more often in the winter when upper respiratory tract infections or colds are most frequent.
- Children are most likely to contract the disease as their immunity against bacteria and viruses is not yet fully developed.
- Risk factors include: a family history of ear infections, exposure to cigarette smoke, poor hygiene, bottle-feeding, pacifier-use, and day-care attendance.
- Follow up examinations are important to minimize the risk of hearing impairment.
Early treatment of otitis media can prevent damage to the middle ear. Antibiotics may be prescribed when the disease was caused by bacteria. Acute otitis media is usually accompanied by pus in the middle ear, fever and ear pain. When otitis media becomes chronic, it may lead to hearing loss because of damage to the eardrum and middle ear structures which transmit sound. An operation is then necessary to restore hearing.
Presbyacusis describes progressive hearing loss in older people and can range from slight to severe hearing impairment.
- Most people over the age of 60 experience some degree of hearing loss as part of the ageing process, as nerve cells in the inner ear, responsible for converting sounds into nervous impulses, begin to degenerate with age.
- Some hearing loss is associated with occupational noise-induced hearing loss. Hearing loss from presbyacusis is irreversible but hearing aids and especially designed equipment can be of great benefit.
Noise-induced hearing loss is the progressive loss of hearing caused by loud noise. It may or may not be accompanied by tinnitus (ringing in the ear). In the beginning the hearing loss and tinnitus may be temporary, but later become permanent if the noise exposure continues.
Characteristics of noise-induced hearing loss are:
- Exposure to harmful sound levels damages the sensitive hair cells of the inner ear.
- Damage can be caused by two kinds of noise: loud impulse noise, such as an explosion and/or shooting, or loud continuous noise, usually over 85 decibels such as that generated for example in a woodworking shop, in a mine and also in an entertainment centre and probably by the excessive use of personal music amplifiers.
- A rough estimate that noise is at a hazardous level is when one cannot have conversation with someone at a distance of 2 metres.
As there is no therapy available to reverse hair cell damage, preventive measures are essential to preserve hearing:
- Education on the harmful effects of loud noise and on noise protection; knowledge of which noises can cause damage.
- Wearing earplugs or other hearing protective devices when involved in a loud activity.
- Promoting and enforcing laws related to occupational safety found in nearly every country.
- Protecting children who are too young to protect themselves.
- Reducing excessive environmental noise.
Ototoxicity refers to medication-caused hearing loss that typically involves damage to the hair cells that convert sounds into nervous impulses in the inner ear and/or to the auditory nerve. It is often but not always accompanied by tinnitus (ringing in the ear).
Ototoxic drugs include certain antibiotics, certain medicines against cancer, certain pain killers and certain diuretics (medicines that increase production of urine).
Frequently used ototoxic drugs are gentamicin (against severe bacterial infections), streptomycin (against TB) and chloroquine and quinine (against malaria).
As there is no therapy available to reverse hair cell damage, preventive measures are important to preserve hearing.
- Awareness and knowledge about ototoxic drugs, amongst the general public and health professionals.
- Drugs that can damage hearing should only be given on prescription by a doctor, who understands the potential risks.
- Throughout therapy with ototoxic medicines, appropriate monitoring of the medicine and the hearing level is necessary, preceded by baseline hearing evaluations and followed by periodic hearing testing.
Tinnitus is a subjective sound in the ears where no external sound is present. Only the person who has tinnitus can hear the noises that range from ringing sounds, hissing to more complex sounds.
The exact physiological causes of tinnitus are not known. However, there are several likely sources known to trigger or worsen tinnitus:
- Noise-induced hearing loss
- Excess wax in the ear canal
- Ear or sinus infections
- Acoustic nerve tumour
- Cardiovascular diseases
If caused by one of the mentioned sources, tinnitus might be reduced when the condition is treated appropriately.
For hard of hearing people, a hearing aid often helps in improving hearing and "masking" the tinnitus noise.
People with chronic tinnitus may be helped by special programmes, called tinnitus retraining therapy, which include counselling and masking which help sufferers to actively concentrate on things other than the tinnitus sound.