Causes of hearing loss
Conductive hearing loss
Conductive hearing loss can be congenital or acquired. Congenital conditions include abnormalities of the pinna, outer ear canal, tympanic membrane and auditory ossicles. Acquired conditions causing conductive hearing loss include perforation of the eardrum and glue ear.
Glue ear is the commonest cause of temporary mild to moderate hearing loss in children. It is due to obstruction of the eustachian tube which runs from the middle ear to the back of the throat, resulting in fluid accumulation in the middle ear. Children under five are the largest group affected, but it can persist into adolescence. It can result in delayed speech development and can affect children’s behaviour and their educational progress.
Changes in behaviour, becoming tired and frustrated, lack of concentration, preferring to play alone and not responding when called may indicate glue ear. These signs can often be mistaken for stubbornness, rudeness and being naughty. As a result many children with glue ear are misunderstood or labelled as “difficult”.
A prolonged period of time with reduced hearing can affect the way in which a child’s speech develops. For example, parts of words may not be pronounced clearly. Children with glue ear may also fall behind at school and become disruptive if they do not have extra support.
Middle ear infection is common in infants and children but can affect people of any age. Acute otitis media is one of the most common illnesses of childhood and is often recurrent particularly up to age 7 years. Eighty to ninety percent of cases of otitis media occur in children under the age of 5 years. Early acute otitis media may predispose a child to develop chronic suppurative otitis media. Other factors like abnormal eustachian tube dysfunction as seen in children with cleft palate and Down’s syndrome, patulous Eustachian tube and systemic immune deficiency are associated with chronic otitis media.
Sensorineural hearing loss
Sensorineural hearing loss can be congenital or acquired. Congenital conditions include -:
- Infections. The most common cause of congenital sensorineural hearing loss is cytomegalovirus (CMV) infection during pregnancy and the resulting hearing loss can be progressive. Much less common congenital infective causes of sensorineural hearing loss include syphilis and toxoplasmosis during pregnancy. Congenital CMV, toxoplasmosis and syphilis may present with delayed onset sensorineural hearing loss months to years after birth. Rubella, once the most common infective cause of congenital sensorineural hearing loss is now uncommon in the UK as a result of effective vaccination programmes.
- Difficulties encountered around the time of birth e.g. prematurity, oxygen deprivation, severe jaundice etc can all cause hearing loss.
- Auditory Neuropathy Spectrum Disorder (ANSD) - can be caused by genetic factors, prematurity, severe jaundice at birth. ANSD causes mild to profound deafness with an additional distortion of sound that makes understanding speech very difficult (over and above what would be expected from the level of hearing loss alone). In severe cases children cannot use hearing aids which amplify the distortion further and may use sign language as their main communication mode. A cochlear implant is an option for some children with ANSD.
- Genetic conditions, either in isolation or part of a named syndrome, are also a common cause of congenital hearing loss. The most frequently encountered genetic syndromes are -:
- Usher syndrome is a condition in which there is an association of deafness and retinitis pigmentosa. Problems with balance are common. The degree of hearing loss in Usher syndrome varies from congenital and total to middle aged onset and partial. Usher syndrome may account for up to 6% of people with congenital hearing loss. There are three types of Usher syndrome, type 1, 2 and 3. Types 1 and 2 are the most common types. The features of the different types are shown in the table below.
| Type 1 | Type 2 | Type 3 | |
|---|---|---|---|
| Hearing | Profound bilateral hearing loss from birth. May obtain little or no benefit from hearing aids. May use a cochlear implant. | Moderate to severe hearing loss from birth. Most can obtain benefit from hearing aids. | Normal hearing at birth. Progressive loss in childhood or early teens. Usually require hearing aids by mid to late adulthood. |
| Vision | Decreased night vision before age 10 with rapid progression to complete blindness. | Decreased night vision late childhood or teens with slower progression than type 1. | Blind spots appear by late teens to early adulthood. Usually blind by mid adulthood. |
| Balance | Problems from birth. Delay in sitting and late walking (18 months). | Normal balance. | Balance usually normal or near normal but problems can develop later in life. |
- Pendred syndrome is a condition which causes hearing loss, and it may also affect the thyroid gland and the vestibular system in the inner ear resulting in an impairment of balance. Hearing loss may start at any time from birth to the age of three. It is progressive but occurs in stages so that after a sudden decrease in hearing the person’s hearing will nearly return to its previous level. Hearing loss is bilateral but often greater in one ear than the other. Some people eventually become totally deaf. About sixty percent of people will develop a swelling of the thyroid gland in the neck (goitre) during their lifetime. Most people do not have balance problems. Some babies may have a delay in walking independently.
- Waardenburg syndrome (WS) is a condition that causes varying degrees of hearing loss and associated skin and hair pigmentation. There are at least four types of Waardenburg syndrome. The most common are types 1 and 2. Type 1 is associated with an unusually wide space between the corners of the eyes. Twenty percent of people with type 1 have hearing loss. People with type 2 do not have a wide space between the inner corners of their eyes, but have many other WS characteristics. About 50 percent of people with type 2 have hearing loss.
- Acquired causes include genetic conditions, infections (usually meningitis), trauma, and ototoxic medications (e.g. certain antibiotics, chemotherapy).
