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Hearing loss is when your hearing worsens, as opposed to deafness, which is when hearing loss becomes total. Hearing loss can occur very gradually, as in age-related hearing loss, or it can be very sudden, as in some viral infections of the inner ear, or trauma.
The ear receives sounds from the environment and transmits them to the brain. It consists of three parts: - Outer Ear: The outer ear includes those parts that are visible on the sides of the head, as well as the canals that enter the head.
- Middle Ear: The canals lead to the eardrum, which is attached to three small bones - the 'ossicles' - that amplify and conduct sound to the inner ear.
- Inner Ear: This consists of an organ called the 'cochlea', which is shaped like a snail shell. The cochlea contains tiny cells called 'hair cells' (which vibrate when a sound is conducted to them via the eardrum and ossicles of the middle ear). The movement of the hair cells transmits electrical impulses down the auditory nerve to the brain. That is when you 'hear' the sound.
Causes & Development; Risk Factors
Two types of hearing loss occur, conductive and sensorineural, depending on which part of the ear is affected. Conductive hearing loss is caused by anything that blocks the conduction of sound from the outer through to the inner ear. As well as those mentioned below, causes include:- collection of fluid in the middle ear ('glue ear' in children)
- blockage of the outer ear (by wax)
- damage to the eardrum by infection or trauma
- otosclerosis, a condition in which the ossicles of the middle ear become immobile because of growth of the surrounding bone
Sensorineural hearing loss refers to damage to the pathway for sound impulses from the hair cells of the inner ear to the auditory nerve and the brain. As well as those mentioned below, causes include:- age-related hearing loss
- acoustic trauma (such as a loud noise) to the hair cells
- viral infections of the inner ear (may be caused by viruses such as mumps, measles, chickenpox)
- certain drugs, such as aspirin, quinine and some antibiotics, affect the hair cells
- acoustic neuroma (a benign - non-cancerous - tumor of the auditory nerve)
- viral infections of the auditory nerve (caused by viruses such as mumps and rubella)
- strokes.
If a pregnant woman has rubella, the foetus is at risk of being born deaf. For this reason, girls are vaccinated against rubella before child-bearing age. Some children are born deaf because of different problems with their development.
Diagnosis & Tests
Hearing loss and deafness are symptoms of the disorders that cause them. Depending on the cause, they may be associated with other symptoms. For instance, disorders that involve the inner ear and auditory nerve often also cause dizziness and tinnitus (ringing or whistling sounds in the ear).
Many tests can be carried out to find the cause of hearing loss. A doctor or audiologist will first listen to the symptoms and perform a thorough examination of the nerves and ears. Tuning forks and a special electronic device with headphones (an audiometer) are used to test the degree of hearing loss and whether it is conductive or sensorineural. Other more complex tests may be carried out to check the function of the eardrum and ossicles.
If a sensorineural cause is suspected, the person may have tests called 'electrocochleography' and 'auditory brainstem responses', which measure the activity of the cochlea, auditory nerve and brain when a sound is heard. None of these tests are uncomfortable. If the cause of the hearing loss seems to be within the brain, the person may have a magnetic resonance imaging (MRI) scan of the brain.
Treatment & Prevention
The treatment of hearing loss depends on the cause. Infections are treated with antibiotics; blockages of the outer and middle ears can be manually cleared; damaged eardrums can be repaired surgically and otosclerosis can be treated effectively by replacement of the affected ossicles with tiny artificial bones. Some causes of sensorineural hearing loss can also be cured. For example, an acoustic neuroma (a benign tumour of the auditory nerve) can be removed surgically.
If there is no cure for the hearing loss (as with age-related hearing loss), a hearing aid usually helps most people, whether the hearing loss is conductive or sensorineural. Many different types of hearing aid are available and a doctor / audiologist will advise as to which type is best. Most people manage very well with a hearing aid and lead perfectly normal lives.
For profound deafness, a cochlear implant may help. This device transmits sound directly into the auditory nerve via an electrical wire implanted into the cochlea. Although the sounds heard are rather 'buzzing' or 'electronic', it can be very useful when used in combination with lip reading. It also lets a person hear the loudness of their own speech and so makes conversation easier. This is most important in deaf young children, as it helps them to develop good speech.
Prognosis
The outcome depends on the cause. It may be temporary as with glue ears in children, curable as with otosclerosis or incurable but manageable as with age-related hearing loss. Only very rarely is hearing loss caused by a more serious condition that affects the brain, such as a tumor.
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Conditions that suggest Hearing Loss:
Risk factors for Hearing Loss:
KEY | | Weak or unproven link |  | | Strong or generally accepted link |  | | Proven definite or direct link |
GLOSSARY
Benign
Literally: innocent; not malignant. Often used to refer to cells that are not cancerous; they tend to grow slowly and don't spread (metastasize) like cancer tumors do.
Dementia (Senile Dementia)
An acquired progressive impairment of intellectual function. Marked compromise exists in at least three of the following mental activity spheres: memory, language, personality, visuospatial skills, and cognition (i.e. abstraction and calculation).
Magnetic Resonance Imaging (MRI)
A technique used in diagnosis that combines radio waves and magnetic forces to produce detailed images of the internal structures of the body.
Meniere's Disease (Menieres, Meniere's, Ménière's)
An affliction of the middle ear characterized by vertigo, nausea, vomiting, tinnitus and progressive deafness.
Multiple Sclerosis (MS)
Demyelinating disorder of the central nervous system, causing patches of sclerosis (plaques) in the brain and spinal cord, manifested by loss of normal neurological functions, e.g. muscle weakness, loss of vision, and mood alterations.
Mumps
An acute infectious disease, caused by a paramyxovirus, and most common in children. Although it usually infects the parotid glands, and is often only a mild condition, it can spread to the testes or ovaries and cause serious problems, particularly when contracted by unresistant adults. A mild child's infection that is not properly monitored holds the potential for pancreatic or meningeal complications.
Nervous System
A system in the body that is comprised of the brain, spinal cord, nerves, ganglia and parts of the receptor organs that receive and interpret stimuli and transmit impulses to effector organs.
Neurofibromas (Neurofibroma, Neuroma, Neuromas, Schwannoma, Schwannomas)
Benign tumors of nerves.
Rheumatoid Arthritis
A long-term, destructive connective tissue disease that results from the body rejecting its own tissue cells (autoimmune reaction).
Seizure (Seizures)
While there are over 40 types of seizure, most are classed as either partial seizures which occur when the excessive electrical activity in the brain is limited to one area or generalized seizures which occur when the excessive electrical activity in the brain encompasses the entire organ. Although there is a wide range of signs, they mainly include such things as falling to the ground; muscle stiffening; jerking and twitching; loss of consciousness; an empty stare; rapid chewing/blinking/breathing. Usually lasting from between a couple of seconds and several minutes, recovery may be immediate or take up to several days.
Tinnitus (Tinnitis)
A sensation of noise (ringing or roaring) that is caused by a bodily condition and can usually only be heard by the person affected.
Virus (Viri, Viruses)
Any of a vast group of minute structures composed of a protein coat and a core of DNA and/or RNA that reproduces in the cells of the infected host. Capable of infecting all animals and plants, causing devastating disease in immunocompromised individuals. Viruses are not affected by antibiotics, and are completely dependent upon the cells of the infected host for the ability to reproduce.
Last updated: Apr 27, 2009
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