Deafness

In this article, you will find an overview of deafness and some of the general issues relating to the management of deafness, including tips on how to consult with a deaf patient. See articles on Deafness in Adults, Deafness in Children and Congenital Deafness for more detail on specific conditions and management options.

The normal hearing range is 0-20 decibels (dB), where 0dB is the threshold for the perception of sound at a given frequency for people with normal hearing.¹ Typical dB levels are around 30dB for a whisper, 50dB for average home noises and 60dB for conversational speech. The pain threshold is at about 140dB (which approximates to the sound of a jet engine). Deafness is a partial or complete loss of hearing, also known as hearing impairment. Hearing loss is measured in decibels hearing loss (dB HL).² It can be graded as follows:³

• 20-40dB HL: mild, cannot hear whispers
• 41-70dB HL: moderate, cannot hear conversational speech
• 71-95dB HL: severe, cannot hear shouting
• >95dB HL: profound, cannot hear sounds that would be painful for a hearing person to listen to.

There are two types of deafness which are not mutually exclusive:

• Conductive hearing loss - this occurs when there is a problem in the transmission of sound waves from the external ear, through the middle ear. The disease processes, which may be congenital or acquired, can occur at any level along this part of the ear and include conditions such as excess ear wax, trauma, otitis externa or media with effusion and otosclerosis.
• Sensorineural hearing loss - this refers to problems occurring in the cochlea (most common site of disease), cochlear nerve or brain stem resulting in abnormal or absent neurosensory impulses. There are also a number of congenital and acquired conditions resulting in sensorineural hearing loss but by far the most common is presbyacusis: age-related hearing loss which may also be associated with tinnitus (ringing, buzzing, whistling, hissing or other noise, heard in the ear in the absence of environmental noise).

Deafness to some degree is a very common problem affecting almost 9 million people in the UK. Of these, profound deafness affects 20,000 children between 0 and 15 years of age, 108,000 people aged between 16 and 60 and a further 580,000 people in the over 60 age group. About 70% of the over 70 year olds have some degree of hearing impairment.

History

This should be taken as for any other problem, taking care to explore possible systemic as well as local causes. Bear in mind that conductive hearing loss is more common in the under 40 age group and sensorineural hearing loss is more likely to occur in older patients.

• Specifically ask about otalgia (ear ache), otorrhoea (discharge), vertigo and tinnitus (more characteristic of noise-induced hearing loss, ototoxicity, presbyacusis and Meniere's disease).¹
• In the systemic review, enquire about diabetes and vasculopathy and ask about use of ototoxic medication.
• Ask about a family history of early hearing loss.
• Don't forget the social history which may reveal frequent visits to noisy environments (leisure or occupational).

Examination

Examination must be both anatomical and functional. Anatomical examination involves inspection of the external ear (note minor disfigurements as the development of the different components of the canal is closely related) and examination of the tympanic membrane, looking for obstructions (cerumen, foreign bodies), evidence of infection, perforation, tympanosclerosis, cholesteatoma or effusion. Functional assessment can be carried out in several ways:

Whispered voice test⁵

This is a simple test to detect hearing impairment in adults and most children (although it is possibly less accurate in the latter). It involves standing at ~ an arm's length (0.6m) behind the patient. The patient occludes the bad ear first (e.g. put finger in ear canal or rub the tragus) and the examiner whispers a number-letter combination (e.g. 1-T-4) as quietly as possible.

This is best done if the examiner quietly exhales and then says the sequence. If the patient incorrectly hears the sequence, try again with another sequence.

They must get at least 3 numbers or letters out of the 6 possible correct ones to deem to have passed. The same procedure is carried out in the other ear with a different sequence.

In children under 12, 'spondee' words can be used (2 syllable words which have the same emphasis in each syllable e.g. base-ball) and in children under 3, spondee words can be used in combination with picture cards to which they can point. However, the younger the child, the less reliable this test is and there is generally known to be some inter-examiner variation. Despite this, it is a useful simple screening tool.

Tuning fork tests⁶

These valuable tests of auditory function enable a distinction to be made between conductive and sensorineural hearing loss. They are based on two principles:

1. The inner ear is normally twice as sensitive to sound conducted by air than that conducted by bone.
2. Where there is purely conductive hearing loss, the affected ear is subject to less environmental noise, making it more sensitive to bone-conducted sound.

Audiometric tests

These enable precise quantification of the degree of hearing loss and help identify the site of pathology. Pure tone audiometry identifies pure tone thresholds for both air and bone conduction. A tympanogram looks at tympanic membrane compliance and is helpful in the diagnosis of perforation, middle ear effusion, ossicular fixation or disruption. Auditory evoked potentials looks at nerve impulses at many sites along the auditory pathway and are helpful not only in evaluating hearing problems but also may be useful in monitoring pharmacological effects of a drug or even coma.

The physical issues¹

Hearing impairment may be a temporary side-effect of a transient problem such as infection (otitis, viral e.g. maternal rubella, mumps, cytomegalovirus) but the sequelae of these may be long-term. Furthermore, there are a variety of syndromes underlying congenital deafness which themselves may be associated with a host of other physical problems: 30-40% of children with hearing problems have associated health needs.² Thus, the patient with hearing loss needs a full examination at initial assessment and a comprehensive review of their problems at further follow-up.

The psychosocial issues

There is no doubt that hearing impairment can have a significant psychosocial impact on the individual. Children's language acquisition and cognitive development can be severely affected (if mild, hearing impairment may present itself as behavioural, cognitive or educational problems)² and in adults, it can affect work prospects and normal integration into society - the elderly being particularly vulnerable.⁵ It is therefore important, on confirmation of the diagnosis, to explicitly explore how the patient is experiencing this psychologically with enquiries into symptoms of depression, as well as what support network is available to the patient. There are a very large number of support groups (see below) but beware of the internet illiterate patient who may not know how to access local help.

General points²

There are considerable fluctuations throughout the UK in the provision of audiological services - both in quantity and quality. Furthermore, there is not always good co-ordination with other relevant services (health, educational, social). This is all the more significant given the fact that age is a major predictor of hearing loss and so as the population ages, more people will be affected. However, changes are being implemented and coupled with improved technology (such as automated triage and audiometry equipment which allows for self-assessment - a process still in its early stages of development with many caveats attached), this picture is likely to change over the years to come. In the case of children, there is a concerted drive to involve the patients and their families in improving the service.

Externally worn hearing aids

These come in a variety of shapes and sizes and many are available on the NHS. They are devices that increase the volume of the sound reaching the ear (effectively, amplifiers). They sit either behind the ear (although these devices are not powerful enough for patients with severe impairment) or just inside. Hearing aids that are placed right inside the external auditory meatus are available for patients with mild hearing loss. Bone conduction hearing aids for patients with conductive hearing loss are available in the form of headbands. Furthermore, hearing aids may be analogue or digital. Analogue hearing aids are slowly being phased out as they are superseded by improving digital aids.² The latter are sometimes known as digital signal processing hearing aids or DSP aids. Aids available on the NHS usually have a digital component to them.

Implantable hearing aids

1. Cochlear implants which are devices designed to stimulate the cells of the auditory spiral ganglion to provide a sense of hearing to those with neurosensory hearing loss. Traditionally, the procedure has been unilateral. It is offered to those patients who have had a minimum of 3 months hearing aid trial (unless there is an underlying ossifying aetiology) on a background of profound sensorineural hearing loss (e.g. 90db HL) and, in children, failure to develop speech, language and listening skills.⁸ More recently, there has been a move towards bilateral implants in a subset of these patients; the British Cochlear Implant Group has set out specific guidance as to which patients in particular should be offered this procedure.⁹
2. Bone anchored hearing aids are reserved for patients with conductive and mixed hearing loss. Surgery involves the fixing of a titanium implant just behind the ear, to which is connected an external abutment and a sound processor. Thus, it allows sound to be conducted through the bone rather than through the middle ear ('direct bone conduction').
3. Auditory brain stem implants are electrodes placed in the cochlear nucleus (in the brain stem).¹⁰ The implant works in conjunction with an external receiver and speech processor. This device converts sounds into electrical signals, which are then sent to the implant.

Adjunctive management

Support groups - there is a significant and active deaf patient support network which patients should be encouraged to contact. Some have an emphasis on practical support, others on emotional support and others still on communicating to deaf people the advances in research. A selection of patient support websites is provided in the Further Reading below. The RNID is a particularly valuable source of a very broad range of information for patients and healthcare professionals alike.

Additional hearing aids - there are a variety of products on the market to assist with hearing. These range from hearing loops to vibrating pagers, visual trigger units for different situations (baby monitors, doorbells, fire alarms) and specialist alarm clocks and telephones, of which Typetalk and Textdirect are examples (see Further Reading). There is also a small but growing community of users of hearing dogs.

Social considerations - children with limited hearing impairment may manage perfectly well in mainstream schools with appropriate help and support but there are specialised schools (listed in the National Deaf Children's Society website) for deaf children. There are also employer legal requirements with regards to hearing disabled people in the work place. Again, these are outlined in the NDCS website with links to further information about patient rights.

Patients with hearing impairment are commonly met in the consultation room, often for unrelated problems. This can sometimes lead to discomfort (at best) and a breakdown in communication (at worst) between the patient and the healthcare professional. There are some simple steps that can be taken in order to minimise these problems and make the consultation as useful as possible for all concerned:

• Ask the patient how they prefer to communicate: don't assume that the patient wearing a hearing aid can automatically follow what you are saying. Ask if they prefer to lip read and have pen and paper handy.
• Sit in good lighting and if possible, away from noise and distractors.
• Make sure you have the listener's attention before you start speaking.
• Do not turn your face away when speaking.
• Speak clearly but not too slowly or using exaggerated mannerisms.
• If they do not understand what you have said, don't just repeat it but try saying it in a different way.
• Don't waffle, avoid jargon and abbreviations.
• Check that the person is following what you are saying.
• In the long term, it is worth investing in a portable hearing loop which can be used in the consulting room.
• If the patient can use British Sign Language (BSL) consider using a suitably trained interpreter or "Sign Translate" via a computer live webcam.¹²