Chapter 43: Deafness and hearing loss

Deafness is defined as impairment of hearing, regardless of its severity.¹ It is a major community health problem requiring a high index of suspicion for diagnosis, especially in children. Deafness may be conductive, sensorineural or a combination of both (mixed).

It is useful to consider the causes of deafness in terms of pathophysiology (conductive or sensorineural hearing loss) and anatomical sites (see FIG. 43.2).

Conductive hearing loss is caused by an abnormality in the pathway conducting sound waves from the outer ear to the inner ear,¹ as far as the footplate of the stapes.

Sensorineural hearing loss (SNHL) is a defect central to the oval window involving the cochlea (sensor), cochlear nerve (neural) or, more rarely, central neural pathways.¹

Congenital deafness is an important consideration in children, while presbyacusis is very common in the aged. The commonest acquired causes of deafness are impacted cerumen (wax), serous otitis media and otitis externa. Noise-induced deafness is also a common problem.

It is important not to misdiagnose an acoustic neuroma, which can present as acute deafness, although slow progressive loss is more typical. A summary of the diagnostic strategy model, which includes several important causes of deafness, is presented in TABLE 43.1 and a checklist of ototoxic drugs in TABLE 43.2.

Symptoms

The symptoms vary so that some barely notice a problem while others are severely disabled.

Common symptoms include inability to:

• hear speech and other sounds loudly enough

• hear speech and music clearly, even when loud enough

• understand speech even when loud enough—a problem of language reception

People with mild hearing loss notice only subtle differences and may have trouble hearing certain high-frequency sounds, such as ‘s’, ‘f’ or ‘th’. They may also have trouble hearing in certain situations, such as at a party or in a crowd where there is a lot of background noise. Those with moderate hearing loss have trouble hearing in many situations.

History

The history should include an account of the onset and progression of any deafness, noise exposure, drug history, a history of swimming or diving, air travel and head injury and family history. A recent or past episode of a generalised infection would be relevant and the presence of associated aural symptoms, such as ear pain, discharge, tinnitus and vertigo. Vertigo may be a symptom of Ménière syndrome, multiple sclerosis, acoustic neuroma or syphilis.

Several important clues can be obtained from the history. The often sudden onset of hearing loss in an ear following swimming or showering is suggestive of wax, which swells to block the ear canal completely.

Patients with conductive loss may hear better in noisy conditions (paracusis) because we raise our voices when there is background noise. Conversely, people with sensorineural deafness (SND) usually have more difficulty hearing in noise as voices become unintelligible.

Examination

Inspect the facial structures, skull and ears. The ears are inspected with an otoscope to visualise the external meatus and the tympanic membrane (TM) and the presence of obstructions such as wax, inflammation or osteomata.

The examination requires a clean external auditory canal. Gentle suction is useful for cleaning pus debris. Syringing is reserved for wax in people with an intact TM and a known healthy middle ear.

It is an advantage to have a pneumatic attachment to test drum mobility. Reduction of TM mobility is an important sign in secretory otitis media.

There are several simple hearing tests. The distance at which a ticking watch can be heard can be used but the advent of the digital watch has affected this traditional method.

Whisper test

Occlude far ear. Have the patient cover near eye with one hand to prevent lip reading. Place your mouth at the near side. Strongly whisper ‘68’ then ‘100’ from a distance of 50 cm. Ask the patient to repeat the words. Then repeat using a normal speaking voice.

Hair-rubbing method

In children and in adults with a reasonable amount of hair grab several hairs close to the external auditory canal between the thumb and index finger. Rub the hairs lightly together at 5 cm (high sensitivity) to produce a relatively high-pitched ‘crackling’ sound (see FIG. 43.3). If this sound cannot be heard, a moderate hearing loss is likely (usually about 40 dB or greater). Like the whisper test, this test is a rough guide only.

Tuning fork tests

If deafness is present, its type (conduction or sensorineural) should be determined by tuning fork testing. The most suitable tuning fork for preliminary testing is the C₂ (512 cps) fork. The fork is best activated by striking it firmly on the bent elbow.

The vibrating tuning fork is applied firmly to the midpoint of the skull or to the central forehead or to the teeth.

This test is of value only if the deafness is unilateral or bilateral and unequal (see FIG. 43.4). Normally the sound is heard equally in both ears in the centre of the forehead. With sensorineural deafness the sound is transmitted to the normal ear, while with conduction deafness it is heard better in the abnormal ear.

Lateralisation of the sound to one ear indicates a conductive loss on that side, or a sensorineural loss on the other side.

The tuning fork is held:

• outside the ear (tests air conduction) and

• firmly against the mastoid bone (tests bone conduction)

Ask which is louder.

It therefore compares air and bone conduction in the same ear (see FIG. 43.5). A variation of the test includes placing the tuning fork on the mastoid process and the patient indicates when it can no longer be heard. The fork is then placed at the external auditory meatus and the patient indicates whether the sound is now audible. Normally air conduction is better than bone conduction and the sound will again be heard.

A comparison of the interpretation of these tests is summarised in TABLE 43.3.

Audiometric assessment

Audiometric assessment includes the following:

• pure tone audiometry

• impedance tympanometry

• electric response audiometry

• oto-acoustic emission testing

Pure tone audiometry is a graph of frequency expressed in hertz versus loudness expressed in decibels. The tone is presented either through the ear canal (a test of the conduction and the cochlear function of the ear) or through the bone (a test of cochlear function).

FIGURES 43.6 and 43.7 are typical examples of pure tone audiograms.

The difference between the two is a measure of conductance. If the two ears have different thresholds, a white noise masking sound is applied to the better ear to prevent it hearing sound presented to the test ear. The normal speech range occurs between 0 and 20 dB in soundproof conditions across the frequency spectrum.

Tympanometry measures the mobility of the tympanic membrane, the dynamics of the ossicular chain and the middle-ear air cushion. The test consists of a sound applied at the external auditory meatus, otherwise sealed by the soft probe tip.

Deafness in childhood is relatively common and often goes unrecognised. One to two of every 1000 newborn infants suffer from SND.¹ Congenital deafness may be due to inherited defects, to prenatal factors such as maternal intrauterine infection or drug ingestion during pregnancy, or to perinatal factors such as birth trauma, and haemolytic disease of the newborn.

Deafness may be associated with Down syndrome and Waardenburg syndrome. Waardenburg syndrome, which is dominantly inherited, is diagnosed in a patient with a white forelock of hair and different coloured eyes.

Acquired deafness accounts for approximately half of all childhood cases. Purulent otitis media and secretory otitis media are common causes of temporary conductive deafness. However, one in 10 children will have persistent middle-ear effusions and mild to moderate hearing loss in the 15–40 dB range.⁶

Permanent deafness in the first few years of life may be due to virus infections, such as mumps or meningitis, ototoxic antibiotics and several other causes.

Screening¹

The aim of screening should be to recognise every deaf child by the age of 8 months to 1 year—before the vital time for learning speech is wasted. High-risk groups should be identified and screened, for example, a family history of deafness, maternal problems of pregnancy, perinatal problems, survivors of intensive care, very low birthweight and gestation <33 weeks, cerebral palsy and those with delayed or faulty speech. The guidelines for early signs of normal hearing are presented in TABLE 43.4.

Optimal screening times:

• 8–9 months (or earlier)

• school entry

There has been a proposition from the National Universal Hearing Screening Committee to introduce testing of newborn hearing following results⁷ supporting this strategy after the finding of a higher incidence than appreciated. The average age at which these deaf children were diagnosed was 26 months.

Early signs of hearing loss

A high index of suspicion is essential in detecting hearing loss in children and any parental concern should be taken seriously. The presentation of hearing loss will depend on whether it is bilateral or unilateral, its severity and age of onset.

Typical presentations include:

• malformation of skull, ears or face

• failure to respond in an expected way to sounds, especially one’s voice

• preference for, or response only to, loud sounds

• no response to normal conversation or to television

• speech abnormality or delay

• absence of ‘babbling’ by 12 months

• no single words or comprehension of simple words by 18 months

• learning problems at school

• disobedience

• other behavioural problems

• inability to detect sound direction (unilateral loss)

• inability to follow simple commands or less than 20 spoken words by 2 years

Screening methods

Hearing can be tested at any age. No child is too young to be tested and this includes the newborn. Informal office assessments, such as whispering in the child’s ear or rattling car keys, are totally inadequate for excluding deafness and may be potentially harmful if they lead to false reassurance.

Pneumatic otoscopy is essential to exclude middle-ear effusions.

Pure tone audiometry is unreliable in children under 4 years of age, so special techniques such as tympanometry are required. Tympanometry assesses TM compliance, and is highly sensitive and specific for detecting middle-ear pathology in children beyond early infancy.

Auditory brain stem response testing is used to evaluate children (particularly young infants) for whom information on behavioural hearing tests is either unobtainable or unreliable.⁶

Management

Children with middle-ear pathology and hearing loss should be referred to a specialist. All children with SNHL (even those with profound deafness), as well as children with conductive losses not correctable by surgery, benefit from amplification. All children need referral to a specialist centre skilled in educational and language remediation.

The prevalence of hearing loss increases exponentially with age. The commonest reason for bilateral progressive SND is presbyacusis, which is the high-frequency hearing loss of advancing age (see FIG. 43.8). There appears to be a genetic predisposition to presbyacusis.⁸

Some features include:

• loss of high-frequency sounds

• usually associated with tinnitus

• intolerance to very loud sounds

• difficulty picking up high-frequency consonants, e.g. ‘f’, ‘s’—these sounds are often distorted or unheard, and there is confusion with words such as ‘fit’ and ‘sit’, ‘fun’ and ‘sun’

Deafness is associated with various types of mental illness in the aged, including anxiety, depression, paranoid delusions, agitation and confusion because of sensory deprivation. The possibility of deafness should be kept in mind when assessing these problems.

Signs indicating referral for hearing test

Possible indications for referring the older person:

• speaking too loudly

• difficulty understanding speech

• social withdrawal

• lack of interest in attending parties and other functions

• complaints about people mumbling

• requests to have speech repeated

• complaints of tinnitus

• setting television and radio on high volume

Sudden deafness refers to sudden SNHL of greater than 30–35 dB with an onset period of between 12 hours and 3 days.⁹ It specially excludes gradual progressive causes of SND, such as cumulative noise trauma or presbyacusis, and also excludes causes of sudden deafness that may be related to pathology in the external auditory canal, TM or middle ear.

The main causes are given in TABLE 43.5.

In several instances, despite a careful clinical examination and investigation, an explanation for sudden SND cannot be found. The cause of deafness in these cases is thought to be either vascular obstruction of the end artery system or viral cochleitis.^7,8 Fortunately, spontaneous recovery usually results.

Patients with sudden SND require immediate referral. It is a difficult problem both in diagnosis and management. Early diagnosis and a high index of suspicion are fundamental.⁸ Two important conditions that deserve special reference are perilymphatic fistula, which occurs after stapedectomy, and an acoustic neuroma presumably causing compression of the internal auditory artery by the tumour in the internal auditory meatus.

Investigations: FBE, ESR, ANCA; TB ELISPOT; viral titres; evoked response audiometry; MRI.

Otosclerosis

Otosclerosis is a disease of the bone surrounding the inner ear and is the most common cause of conductive hearing loss in the adult with a normal tympanic membrane. The normal middle ear bone is replaced by vascular, spongy bone that becomes sclerotic.

Clinical features³

Usually:

• a progressive disease

• develops in the 20s and 30s

• family history (autosomal dominant)

• bilateral or unilateral

• female preponderance

• affects the footplate of the stapes

• may progress rapidly during pregnancy

• conductive hearing loss

• begins in lower frequencies, then progresses

• SND may be present

• impedance audiometry shows characteristic features of conductive loss with a mild sensorineural loss

• may be associated with Ménière syndrome

Management

• Referral to an ENT consultant

• Stapedectomy (approximately 90% effective)

• Hearing aid (less effective alternative)

Cholesteatoma⁷

A cholesteatoma is a sac of keratinising squamous epithelium that arises from a perforation involving the periphery of the TM. In other words, it is a ‘big sac of skin’ (refer to CHAPTER 50). It is dangerous to the ear because it tends to expand and destroy adjacent structures, including the TM, ossicular chain and cochlear. Destruction of the first two may result in conductive hearing loss of up to 60 dB. Irreversible SND caused by otic capsule erosion may also occur. Surgical correction is mandatory.

Wax impaction¹⁰

Ear wax impaction occurs in about 5% of the normal population but is more prevalent in older people especially with the use of hearing aids. It is also common in those who use cotton buds (which should be avoided), where cerumen is packed onto the TM leading to a conductive hearing loss. The average wax production is 2.81 mg/week. Most ear wax clears spontaneously without treatment.

Methods of removal include:

• gentle syringing with warm (body temperature) water or normal saline solution—by trained practitioner (avoid syringing if infection or perforated TM)

• consider cerumenolytic drops for several days before syringing

  • — carbamide peroxide (Ear Clear)

  • — docusate sodium (Waxsol)

  • — hydrogen peroxide

  • — sodium bicarbonate

  • — oil based (e.g. olive oil, almond oil)

Keratosis obturans is an accumulation of keratin to form a pearly-white plug that requires removal.

Noise-induced hearing loss

Clinical features

• Onset of tinnitus after work in excessive noise

• Speech seems muffled soon after work

• Temporary loss initially but becomes permanent if noise exposure continues

• High-frequency loss on audiogram

Sounds exceeding 85 dB are potentially injurious to the cochlea, especially with prolonged exposures. Common sources of injurious noise are industrial machinery, weapons and loud music.

Tinnitus

The diagnostic strategy is presented in TABLE 43.6.

Tinnitus is defined as a sound perceived by the ear that arises from an internal source. When pathology in the inner ear is the cause, the tinnitus is non-pulsating, continuous and may have variable frequencies and intensity.

A thorough history and examination should be conducted so that tinnitus can be classified as objective (e.g. heard with stethoscope) or non-objective and pulsatile, or non-pulsatile.

Precautions:

• exclude wax, drugs including marijuana, NSAIDs, salicylates, quinine and aminoglycosides,⁹ vascular disease, depression, anaemia, aneurysm, vascular tumours (e.g. glomus tumour), venous hum (jugular vein), acoustic neuroma (progressive and unilateral), Ménière syndrome and infections (e.g. viral cochleitis)

• if pulsatile, consider carotid artery lesions, including a caroticocavernous fistula and an AV fistula

• beware of lonely elderly people living alone (suicide risk)

Note: Otosclerosis in young adults causes deafness and tinnitus.

Investigations

• Audiological examination by audiologist

• Tympanometry and speech discrimination

• MRI or CT scan (if serious cause suspected or head injury)

Management

• Treat any underlying cause and aggravating factors. Otherwise, minimise symptoms.

• Educate and reassure the patient (tinnitus is nearly always amenable to treatment).

• Encourage a patient support group.

Mainly based on acoustic desensitisation:

• Relaxation techniques, address any anxiety

• Tinnitus retraining therapy (clinical psychologist)

• Cognitive behaviour therapy techniques

• Background ‘noise’ (e.g. music played during night for masking)

• Tinnitus maskers

• Hearing aids (based on audiologist assessment)

• Consider hypnotherapy

• Clonazepam 0.5 mg nocte (with care)

• Minerals (e.g. zinc and magnesium)

• Betahistine (Serc) 8–16 mg daily (max. 32 mg)

• Carbamazepine or sodium valproate

• Antidepressants if depressed

• Lignocaine 1% IV slowly (up to 5 mL)

Hearing aids are most useful in conductive deafness. This is due to the relative lack of distortion, making amplification simple. In SND the dual problem of recruitment and the hearing loss for higher frequencies may make hearing aids less satisfactory. Modern aids selectively amplify higher frequencies and ‘cut out’ excessive volume peaks that would cause discomfort. A trial of such aids should be made by a reliable hearing-aid consultant following full medical assessment.

The cochlear implant or ‘bionic ear’ is used in adults and children with severe hearing loss unresponsive to powerful hearing aids. The implant consists of an array of 22 electrodes inserted into the cochlea following mastoidectomy, attached to a receiver implanted in the skull next to the ear. External sounds are detected by an external processor worn behind the ear and connected to the implanted receiver with an external induction coil. Near normal speech and hearing may be achieved in children with congenital or acquired deafness with early implantation. The device is most suitable for children over 2 years and adults with severe deafness.

Relatives and close friends need considerable advice about coping with deaf family members. They should be told that the deaf person may hear in a quiet room but not in a crowd, and advised of the range of aids and services available and the importance of proper maintenance of any hearing aids (especially with aged people).

Do

• Face the light when speaking to them.

• Speak directly to them.

• Speak clearly and naturally.

• Speak at a uniform pitch: avoid lowering your voice during or at the end of a sentence.

• Speak within 2 metres.

• Be tolerant and relaxed.

• Be patient with mistakes.

• Write key words on a paper pad when necessary.

Don’t

• Speak with your back to them.

• Mumble your words.

• Use exaggerated lip movements.

• Shout.

• Put your hand or fingers over your mouth when talking.

• Repeat one word over and over.

• See ‘Red flags’ above.

• Sudden deafness.

• Any child with suspected deafness, including poor speech and learning problems, should be referred to an audiology centre.

• Any child with middle-ear pathology and hearing loss should be referred to a specialist.

• Unexplained deafness.

Hand-out sheets from Murtagh’s Patient Education 7th edition:

• Hearing problems in children

• Hearing impairment in older people

• Tinnitus