Causes Of hearing loss
What are some causes of hearing loss?
There are many causes of hearing loss and many different ways of explaining or classifying them. This article covers causes of hearing loss acquired from childhood onwards.
A straightforward way of categorising causes of hearing loss is based on the type of hearing loss, and how it relates to the part of auditory or hearing system. Often, hearing loss is accompanied by tinnitus (ringing noises in the head or ears) and sometimes by a balance problem.
These are the main causes of hearing loss affecting one or more of these four parts of the auditory system:
The outer ear which includes the external ear on each side of the head, sometimes called the pinna or auricle, the ear canal and the eardrum.
The middle ear which also includes the eardrum and the middle ear bones (called the ossicles or ossicular chain) within the middle ear cavity.
The inner ear which has two main sections, the cochlea for hearing and the vestibular system for balance.
The central auditory system which has highly complex nerve pathways connecting the cochlea (inner ear) to the hearing centres of the brain (auditory cortex).
What are some Types of hearing loss?
Conductive hearing loss
Conditions affecting the outer and/or middle ear cause conductive hearing loss which is often treatable and may, therefore, be temporary.
Sensorineural hearing loss
Disorders of the inner ear or central auditory system cause sensorineural hearing loss which is usually not medically or surgically treatable and is, therefore, generally permanent.
Mixed hearing loss
When there is both a conductive and sensorineural loss, this is called a mixed hearing loss.
The onset of a hearing loss can be sudden (within a few days), rapid (within a few months) or slowly progressive (over years rather than months). Sudden hearing loss is classified as a medical emergency and should always have urgent, hospital treatment.
Causes of hearing loss - Conductive (outer and/or middle ear)
Trauma & inflammation
The external ear (pinna or auricle) can be damaged by trauma or inflammation or there can be a congenital abnormality, i.e. present at birth. Noticeable hearing loss will only arise if the entrance to the ear canal is obstructed or closed up preventing sound entry.
The ear canal conveys sound to the eardrum and any blockage in the ear canal prevents sound transmission. Excessive wax is the most common cause of hearing loss.
Otitis externa (Swimmer’s Ear)
Any swelling in the ear canal due to allergy, skin infection or inflammation (called otitis externa) can affect hearing. The eardrum, as part of the outer ear, can easily be affected by infection or inflammation of the ear canal (otitis externa).
Foreign bodies in the ear canal can block the passage of sound.
The eardrum is also vulnerable to perforation and subsequent infection if anything is pushed too far into the ear canal. Perforations of the eardrum are usually due to middle ear inflammation/infection (otitis media) usually resulting in a discharge from the middle ear into the ear canal as well as hearing loss. A blow to the side of the head, especially against the pinna, can also cause the eardrum to rupture.
Otitis media (Middle Ear infection / glue ear)
A healthy middle ear cavity is filled with air and is ventilated by a narrow tube (the Eustachian tube) between the middle ear and the back of the nose. Nasal congestion, commonly from an upper respiratory tract infection can prevent the Eustachian tube from supplying air to the middle ear and draining any fluid which encourages middle ear inflammation and infection (otitis media). This is a particular problem in young children but also affects adults.
Otitis media affects the health and function of the eardrum and the ossicular chain; it is the most common cause of middle ear hearing loss.
This is a potentially dangerous condition, which can impact all structures in the middle ear and beyond, is cholesteatoma. It is a benign growth which starts within a retracted section of the eardrum resulting from a sustained, abnormal middle ear pressure. It gradually enlarges, not only resulting in hearing loss but, if left untreated surgically, it can be life-threatening from complications such as infection of the bone of the skull, lining of the brain and even the brain itself.
Any abnormal pressure in the middle ear cavity, due to inadequate ventilation and drainage of the middle ear cavity, can put the eardrum under such stress that it perforates. Significant atmospheric pressure changes, such as when flying or diving, can cause pain and hearing loss sometimes resulting in eardrum rupture (called barotrauma).
The chain of three tiny bones in the middle ear (ossicles or ossicular chain) transmit sound vibrations from the outer ear to the cochlea in the inner ear. These tiny bones can suffer dislocation from head trauma such as in a road traffic accident or in contact sports such as boxing or rugby.
Apart from the effects of middle ear inflammation and infection, the most common condition affecting the ossicular chain in adults is otosclerosis. Otosclerosis is essentially a hardening of the bones of the ossicular chain. This is a hereditary condition but, because as it does not appear in every generation of an affected family, the genetic connection is often not obvious.
The hearing loss becomes noticeable usually before the middle years of adulthood but is highly variable in onset. Fortunately, otosclerosis can be successfully treated surgically but, for those who do not wish to have surgery or where surgery is only partially successful, hearing aids are usually very effective.
Causes of hearing loss - Sensorineural(inner ear to the brain)
Age-related hearing loss (presbycusis)
Presbyacusis affects the majority of those over 60 years of age and certainly those over 70 years. It is one of the most common causes of hearing loss. All parts of the auditory system are affected by ‘wear and tear’ but particularly the cochlea and its associated nerve pathways to the brain.
Typically, at least in the earlier stages, it affects hearing sensitivity to higher-pitched sounds which can have a marked effect on understanding speech especially in difficult listening conditions such as in background noise. Tinnitus may also occur.
Noise Induced Hearing Loss (NIHL)
Exposure to excessive noise / prolonged acoustic trauma are generally considered to be the second most common causes of hearing loss. The delicate sensory cells in the cochlea (‘hair cells’) can be damaged by loud noise. The higher the noise level or the longer the duration of exposure, the greater is the likelihood of permanent hearing loss.
Increasingly, irreversible noise damage results from listening to loud music using earbuds or earphones with smartphones or other personal devices. NIHL is now affecting an increasingly younger age group.
Cardiovascular disease is a significant component in age-related hearing loss. However, it can affect a person of any age when the blood supply to the inner ear or hearing centres in the brain is significantly reduced or stops altogether.
The cochlea in the inner ear is highly sensitive to a reduction in blood supply which can cause irreversible damage. Hardening of the arteries (arteriosclerosis), high blood pressure, thrombosis, stroke and heart attack can all result in hearing loss which is usually permanent.
There are many infectious diseases, bacterial and viral, which can cause sensorineural hearing loss with some of them typically affecting one ear only. Although not a full list, the more common ones are measles, mumps, meningitis, chicken pox, shingles and influenza.
Some medications are known to cause sensorineural hearing loss and these are called ototoxic drugs. Nowadays, these are only used for life-threatening conditions such as certain cancers or serious infections.
Even over-the-counter medications such as aspirin can cause hearing loss if taken in regular, larger doses but usually the hearing loss is reversible once the medication is stopped.
Meniere’s disease is the most common condition involving both hearing loss and balance problems, often with tinnitus in one or both ears. The exact cause of Meniere’s disorder is not known may involve a number of possible causes.
Sudden attacks of dizziness are a particularly unpleasant aspect of this condition which are often accompanied by a fluctuating hearing loss and low-pitched tinnitus.
Even when the dizzy spells stop happening, a permanent hearing loss with persistent tinnitus usually results, sometimes with one ear being much worse than the other.
Hereditary or genetic hearing loss does not always means a person is born with it. Genetic hearing loss can have a late onset, for example in patients with Ushers Syndrome which involves progressive loss of both vision and hearing.
Genetic influence can be very difficult to establish as one of the causes of hearing loss. However, it is thought that this is a factor for some people as to when age-related hearing loss begins to occur; and may even mean some people are more susceptible to hearing loss from noise exposure.
Age-related hearing loss is not only due to deterioration in the cochlea of the inner ear as explained above.
Ageing can also mean that the auditory nerve and hearing centres in the brain can lose the ability to process sound efficiently causing particular problems with more complex sounds such as speech or music.
A benign tumour called an acoustic neuroma or vestibulocochlear schwannoma can also be one of the causes of hearing loss. It normally grows very slowly, gradually compressing the auditory nerve and may also affect the nearby vestibular (balance) nerve resulting in both hearing loss and balance problems often with tinnitus. The hearing symptoms are almost always just on one side (unilateral).
Bilateral tumours are even rarer and are usually associated with a hereditary condition called neurofibromatosis type 2 (NF2).
Although the subject of much ongoing research, it is clear that there is an association between untreated/unassisted hearing loss and cognitive decline and dementia. It is not yet fully understood how unassisted hearing loss can accelerate the onset of cognitive decline and dementia.