Childhood hearing loss

Introduction

Homo sapiens stands apart with a highly developed system of communication. Any impairment that interferes with our ability to communicate threatens our integration in society. Childhood hearing loss is taken seriously by all and significant resources are expended in prevention, detection and management.

Childhood hearing loss not only affects speech and language development but also cognitive; social and emotional development.

The challenge of early detection and intervention in severe and profound sensorineural hearing loss has to be balanced with a more expectant and conservative approach in the commonest type of childhood hearing loss from otitis media with effusion. Technological advances have improved early detection and paediatric cochlear implantation is nothing short of a miracle. Working with hearing impaired children requires a team approach and good communication with community workers and schools.

Early detection of hearing loss: Universal neonatal screening

Screening only those children with selected risk factors is inefficient as 95% of children with one or more risk factor will have normal hearing. Conversely, half of children eventually shown to have sensorineural hearing loss will have no risk factors. This realisation has prompted a progressive change to Universal Neonatal Hearing Screening. This has been shown to increase detection rates and decrease the age of detection with benefits in speech and language development.

Ideally, screening protocols should only pass neonates with normal hearing accepting that some who fail may eventually also be shown to have normal hearing after subsequent testing. The tests should be relatively cheap and require minimal training. Most programmes are based on a mixture of otoacoustic emissions (OAE) and brain stem evoked responses (BSER), either using both or a 2 tier system with initial screening with OAE. Support and information must be given to parents who have failed a screening test as they wait anxiously for the next level test.

OAE are acoustic responses of the cochlear to auditory stimulation. They are present in neonates with normal hearing so long as the external and middle ear are also normal. Middle ear effusions or canal debris can affect the results as can testing in a noisy environment. OAE test outer hair cell function so rare abnormalities of the inner hair cell or auditory nerve will be missed.

BSER are responses to auditory stimulation recorded from scalp electrodes. The stimulus is a non frequency specific click. Automated detection algorithms are used in screening to give a pass/fail equivalent to about 30-35 dB nHL.

Early provision of Hearing aids

Early detection of hearing loss is useless without prompt further assessment, confirmation of loss and most importantly, early provision of hearing aids. Alongside early aiding, support, information and counselling is needed for the family.

Further investigations in neonatal deafness

Neonates who fail screening and have a genuine hearing loss confirmed, warrant further investigation. This includes those who have survived prematurity, as prematurity without significant hypoxic episodes or ototoxicity does not itself seem to cause deafness. Investigations will include blood tests as well as an ECG and genetic testing. Protocols are evolving which rely more heavily on genetic testing as this becomes more widely available. Connexin 26 mutations are the commonest cause of non syndromic deafness accounting for 50% of all autosomal recessive non-syndromic hearing loss in Caucasians.

Childhood audiometry

Despite universal neonatal hearing screening it is important to test the hearing of children at older ages as well. This will pick up those who have progressive or acquired nerve deafness as well as the common condition of glue ear. Some children will be identified at screening while other children will present to their GP with a suspected hearing loss.

Children from 6 months to 18 months can be tested by distraction testing. Here they sit on their mother’s knee and their attention is on a visual stimulus in front of them. This stimulus is withdrawn leaving them in a state optimised to receive an auditory stimulus from the side which prompts a head turning response. Properly conducted with an experienced team in a sound proofed room this can give accurate frequency specific information for each ear separately. A development is to reward an appropriate head turn with a visual “treat” such as a moving toy. This is visually reinforced audiometry.

Older children from 2 ½ to 3 years onward can perform conditioned audiometry. They are taught to respond to sounds by performing a task such as putting men in a boat. Once the game is established the amplitude is reduced to threshold and different frequencies tested. In the youngest this may have to be free field but once headphones are tolerated each ear can be tested accurately. Older children can respond with a button as in adult testing.

Impedance testing is often used in general practice and school as it is quick and objective but it does not test hearing. It tests the ability of the middle ear to absorb sound at different ear canal pressures. It can show the presence of middle ear effusions as well as perforated or hypermobile tympanic membranes.

Otitis media with effusion; glue ear

Middle ear effusions are common in children and can be asymptomatic. Effusions can however be associated with frequent recurrent ear infections and/or with significant hearing loss and with subsequent speech, social and educational delay. It is clear that glue ear is not a discrete condition with a simple management plan that fits all. As it is common and self-limiting, the initial approach to investigation and intervention should be conservative and should generally include a period of “watchful waiting”.

The history is important to asses the impact of the condition in the individual child. A typical presentation with hearing loss would include inattention, variable response to commands, high volume levels for television and poor articulation. The level of competing noise at school or in the home is important as it affects the child’s ability to cope with a hearing loss. Speech delay is assessed in young children by vocabulary, articulation and the development of language as evidenced by the number of 2 to 3 word utterances. In older children, articulation is the key area affected by hearing loss in glue ear. Frustration is a common finding in younger children with speech delay secondary to glue ear with consequent poor behaviour at nursery.

In children with ear infections associated with glue ear the age of the first infection is a good prognostic indicator of future troubles. It is important to try to decide if the ears return to normal in between infections “discrete infections” , whether the infection recurs after a short course of antibiotics “inadequately treated infections” or if separate infections are occurring on a background of quiescent glue ear “recurrent infections”. A history of snoring and mouth breathing may suggest associated adenoid hypertrophy.

Examination of the ear may show a dull grey, plum or yellow membrane. Fluid levels and bubbles show that at least some air is present in the middle ear. Balance and gait may be affected. Simple conversational test in the office are useful as a guide and to help parents understand the level of hearing loss from glue ear.

Age appropriate audiometry is important though levels will fluctuate as glue ear is a seasonally fluctuant condition. The pattern seen on typmanometry affects the likelihood of an effusion being present. The flat line “B” type trace has a 80% likelihood of effusion whilst the “normal” “A” trace has less than 5% chance of an effusion.

Treatment is expectant, medical or surgical. A period of 3 months “watchful waiting” is recommended. If presentation is delayed this period may have elapsed by the time of presentation. During the waiting period cows protein free diets can be tried as can homeopathic remedies. There is no evidence to support cranial osteopathy for glue ear. Medical treatment is either antibiotics or steroids. Long courses of low dose broad spectrum antibiotics (such as Co-Amoxiclav) have a small, medium length benefit in clearing effusions but are particularly useful in controlling the infections in recurrent acute otitis media with effusion. Oral steroids are effective and there may also be a small benefit from nasal inhaled steroids. Medically it would seem reasonable to offer antibiotics if glue ear is associated with infections and to try inhaled steroids if there is a history of allergy.

Tympanostomy tubes or Grommets.

Surgical drainage of middle ear effusions alone gives a short lived benefit with re-accumulation of fluid in most cases within 6 weeks. Laser myringotomy under local anaesthesia is not practical in most children. Surgical treatment for most children consists of drainage followed by placement of a ventilation tube which typically will last up to a year. After this time there is little long term benefit of ventilation tubes unless tubes that are designed to stay longer are used. These typically have a higher chance of being complicated by a perforation.

Many protocols have been developed to decide which children with glue ear should be offered tubes. A moderate hearing loss of over 30dB is a fair consensus but the effect of the loss on the child and in particular speech delay is a factor. Educational difficulties and behavioural problems from frustration with poor speech all need to be put into a balanced decision with parental guidance. Parents need to be offered alternatives including no treatment or amplification. They need to realise that the tubes are designed to be extruded and that a proportion of children may need a further set of tubes.

The majority of children suffer few complications from tube insertion other than occasional discharge and minor tympanosclerosis of the membrane which does not affect the hearing. Major anaesthetic complications in children undergoing tube insertion alone have not been reported.

Discharge that persists should be sent for culture and oral treatment started. If the organism is not readily treatable orally, antibiotic ear drops need to be used. Some are ototoxic though it is unclear if this is a theoretical or genuine but very rare risk. Topical ciprofloxacillin available as eye drops is safe and effective for pseudomonas.

There is no clear evidence to stop children swimming which is an important life skill and part of school life for many. A few children have repeated episodes of discharge and this group should probably wear silicone or customised ear plugs, drying the canal after swimming with a hair dryer if practical.

Children with tubes need a follow up to check normalisation of the audiogram and further checks until the tube has extruded to identify rare sequelae such as cholesteatoma and perforation.

Adenoidectomy

Adenoidectomy helps resolution of glue ear even if the adenoids are not enlarged and there are no symptoms of obstruction. Combining adenoidectomy with tube insertion offers the medium term benefit of ventilation tubes with the longer term benefit of adenoidectomy. Newer techniques such as suction diathermy avoid bleeding and have a very low recurrence rate. There remains the small risk of hypernasality which may be an expression of a submucous cleft palate.

Other causes of conductive deafness in children

Conductive deafness in the absence of perforation or effusion is due to ossicular fixation or discontinuity. Both are rare in non-syndromic children. Children with Treacher-Collins, Aperts, Crouzons, CHARGE Down’s and hemifacial microsomia. In some the outer ear and pinna are unaffected but in other there is a variable degree of canal stenosis or atresia and microtia.

Bone anchored hearing aids for conductive hearing loss

These aids stimulate the intact cochlear by bone conduction, bypassing any cause of conductive deafness and avoiding the problems of bone conducting aids of the “Alice band” type. They are used when a conventional aid cannot be used because of meatal atresia or discharge. Originally developed for dental implants, osseointegration techniques allow secure fixation of hearing aids with a fixture surrounded by living bone and no intervening capsule. They penetrate the skin without infection. The aids are mounted on the fixture with a quick release collar or abutment. Placing the fixture usually requires 1 or 2 procedures and the site needs to be kept clean. The hearing benefit is excellent.

Cochlear Implants for profound hearing loss

In some children, hearing loss is so severe that they derive little benefit from conventional hearing aids. This group can be helped by direct stimulation of the auditory nerve with a multi-channel implanted wire within the cochlea. Sound is picked up externally by a microphone and amplified, filtered and coded in the external speech processor. The coded signal is then relayed to an implanted device by an external coil held in place with a magnet. The internal device deciphers the coded signal and separates it into the different channels of the wire within the cochlea. The signal is based on speech but is not just an amplified and filtered speech signal. Different strategies have been developed to code the signal which is presented to the channels of the implant which represent regions of the cochlea. Even adults, who lose hearing but already have speech, take time to interpret the coded signal. Children implanted very early, before they have developed speech, tend to do very well because of the tremendous plasticity of the brain at that early stage. At present the lower age of implantation in congenital deafness is about a year. Below this it is difficult to establish hearing levels and to have an effective trial of hearing aids. In a situation which mirrors the gradual provision of bilateral hearing aids, the provision of bilateral cochlear implants is becoming more common. As the technology improves and surgery becomes ever more routine the level of hearing loss that justifies a cochlear implant is gradually reducing so that now children are implanted who could gain benefit from conventional aids but who will gain more benefit from an implant

Education and support

Any child with a persistent hearing loss benefits from experienced professional support in the educational environment to ensure that teachers are aware of the extent of the loss and how best to overcome it. FM signals from a teachers microphone received by the child’s hearing aid give clear sound without the amplified background noise which bedevils conventional hearing aid use.

The future is very bright for hearing impaired children with technology improving conventional aids and cochlear implants. In time it may be possible to regenerate lost hair cells to improve hearing in a truly remarkable and physiological way.

1. Hemifacial microsomia

2. Stickler syndrome

3. Congenital cytomegalo virus

4. Usher syndrome

5. Branchio-oto-renal syndrome

6. Pendred syndrome

7. CHARGE Association

8. Neurofibromatosis type II

9. Mitochondrial disorders

10. Waardenburg syndrome

http://www.biomedsci.creighton.edu/faculty/he.html

to see outer hair cell responding to music