deafness

Deafness and Tinnitus

Anatomy and Physiology Type of Hearing Loss Conductive Hearing Loss Otosclerosis Sensorineural Hearing Loss (SNHL) Congenital SNHL Presbyacuisis Noise induced hearing loss (NIHL) Ototoxicity Systemic disease Acoustic Neuromas Tinnitus Treatment of Hearing loss

Anatomy and Physiology
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Type of Hearing Loss

Hearing loss may be either sensorineural or conductive or a mixture of the two (mixed hearing loss)

A sensorineural hearing loss is caused by dysfunction in the cochlea or the higher auditory pathway including the cochlear nerve. Sometimes a cochlear loss is referred to as sensory and one involving the nerve or higher centres neural.

Conductive hearing loss is caused by a mechanical obstruction to the transmission of sound energy anywhere from the outer ear to the stapes and the oval window.

Conductive Hearing Loss

Congenital

Congenital causes of conductive hearing loss are relatively rare and usually arise in malformations of the external and middle ear such as microtia. This may occur as an isolated event or as a part of a more complex problem such as Treacher Collins or Goldenhar syndromes.
Occasionally there may exist abnormalities of the middle ear and ossicles such as ossicular fixation.

Depending on the severity of the abnormality, the treatment of this condition may involve reconstructive surgery of the outer and / or middle ear, or provision of suitable hearing aids.

Acquired

Potential causes can be listed in anatomical terms depending on the site of the obstruction.

External ear

Foreign bodies: Earwax is often blamed for hearing loss. In fact it rarely causes a significant loss. Around 90% of the ear canal must be obstructed for wax to cause a hearing loss. Occasionally if a smaller amount of wax is pressed up against the drum, this can cause hearing loss by impeding the drum movement.

Other foreign bodies include cotton wool buds, beads, dressings and even insects. Removal of these will improve the hearing, but the patient will often present with symptoms other than hearing loss.

Infection in the external ear (otitis externa) will affect the hearing if the canal becomes sufficiently swollen or blocked with debris to obstruct the passage of sound.

Stenosis of the canal is rare, but may occur after chronic infection, surgery or radiotherapy.

Tympanic Membrane

Perforations of the tympanic membrane may cause hearing loss. Small perforation are unlikely to lead to a significant loss unless their presence leads to a middle ear infection. Larger perforations lead to a hearing loss because there is not enough area of tympanic membrane remaining to absorb and transmit sound energy.

Tympanosclerosis a deposit of chalky calcium debris within the substance of the drum usually leads to no loss. If there is considerable tympanosclerosis, the resulting inflexibility of the drum will lead to a mild loss only. Normally, mild tympanosclerosis is clinically unimportant.

Retraction / Atelectasis where the drum becomes thinned by ongoing disease such as eustachian tube dysfunction, the drum may become thinned and draped over the ossicular chain and middle ear. This impairs the conduction of sound energy and may eventually lead to erosion and loss of the ossicular chain.

Middle Ear

A pathological process within the middle ear usually causes a hearing loss.

Infections and cholesteatoma - acute otitis media see section on otalgia and perforations
Acute otitis media will cause a temporary hearing loss. As the infection resolves there may be a persisting effusion which prolongs the loss.

Middle ear effusion - Glue ear - see section on glue ear in children The hearing loss in glue ear (OME) can be minimal or quite significant, as much as 40 dB. Untreated this can lead to problems at school (as children fail to hear the teacher), speech delay and behavioral problems. It is not certain if untreated children eventually catch up after the resolution of the disease, but in general in the UK, if the disease is thought to be leading to such problems it is generally treated.

Haemotypmanum - blood in the middle ear. Usually as a result of injury including skull fracture, or barotrauma - diving or aviation. This usually leads to a 30-40dB conductive loss and resolves spontaneously. The drum often looks brown or black / blue as the haemoglobin degrades.

Ossicular chain - the ossicular chain may be interrupted by disease such as cholesteatoma. Usually the long process of the incus is lost first, because of its poor blood supply. As the disease worsens, the stapes may also be eroded. It is unusual for the malleus to be eroded by chronic infection. The chain may also be damaged by head injury of direct trauma (e.g. foreign body in the ear canal) or by surgery to the middle ear (iatrogenic). The chain may become fixed as a result of chronic disease.

Otosclerosis

New spongy bone is laid down around the footplate of the stapes which impedes its ability to move freely in the oval window. This causes a conductive deafness which gets worse as the disease process develops.
Commoner in women with a family history in 50% of cases, the disease progression can be worsened by oestrogens although oestrogens do not actually cause the underlying disease. This is why hearing can deteriorate during pregnancy, or in women on hormone treatment or the contraceptive pill. The risk for most women on the pill is slight, although patients with suspected or proven otosclerosis may be better switching to a progesterone only pill or an alternative method of contraception.
Affected patients often speak in a low, quiet voice (c/w sensorineural loss) and can sometimes hear better in the presence of background noise (c/w sensorineural loss). Tinnitus can be a feature, especially in rapidly progressive disease. The condition is painless. In severe cases, the labyrinth may be affected with ossification occurring in the turns of the cochlea itself, leading to a mixed hearing loss.
Examination is normally normal although in very active disease it may be possible to see a pink hue to the drum, from very vascular spongy bone deposits on the medial wall of the middle ear. (Schwarze's sign).
Tuning fork examination and pure tone audiometery should confirm a conductive loss. Middle ear pressure measured on l should be normal.

Conductive hearing loss with a normal tympanic membrane is suspicious of otosclerosis

If the hearing loss is slight, no treatment may be needed. More significant loss (particularly with a negative Rinne test) may be treated with a hearing aid or surgery. Surgery involves replacing the stapes super-structure with a prosthetic piston, placed into a hole drilled in the footplate and connected to the incus. (Stapedectomy). Because part of the stapes is left in situ, the procedure is more correctly referred to as a stapedotomy . The results of this procedure are very good in the majority of cases, although there is a slight risk of worsening the hearing and post-operative vertigo.
Very severe cases of cochlear otosclerosis with sensorineural loss have been treated with cochlear implantation.

Sensorineural Hearing Loss (SNHL)

With sensorineural loss, it is not only the volume of sound that is reduced, the actual content will be more difficult to interpret. This is known as reduced discrimination and is particularly significant in neural rather than sensory causes of deafness. This can make hearing aids less useful than one might expect given the hearing loss on the audiogram.

Congenital SNHL

Congenital SNHL may be inherited, due to structural abnormalities in the labyrinth, acquired prenatally, during birth or in the neonatal period. Some causes are idiopathic

Inherited SNHL may be an isolated defect restricted to the hearing, or as part of an eponymous inherited syndrome, examples include:

Usher's (with retinitis pigmentosa),
Waardenburg (with white forelock, broad nasal bridge, telecanthus and heterochromia iridis- different coloured irises)
Allport (with inherited nephritis)
Jervell Lange-Nielson (with cardiac conduction anomalies - prolonged QT interval)

Pre-natal SNHL is commonly caused by viral infection in utero especially Rubella, and CMV. Less common causes include influenza, toxoplasmosis and syphilis. Some drugs may be ototoxic to the foetus as well as the adult (aminoglycosides).

Natal-Neonatal The commonest causes in this group are birth anoxia and kernicterus. (severe neonatal jaundice leading to injury to the basal ganglia)

Structural anomalies usually involve failure of the nerves or bony structures of the cochlea to develop normally. These include the rare Mondini and Schiebe dyplasias. they are diagnosed with high definition CT scans of the temporal bone.

Natal-Neonatal The commonest causes in this group are birth anoxia and kernicterus. (severe neonatal jaundice leading to injury to the basal ganglia)

Presbyacuisis

Over the age of 55 or so, most people to a greater or lesser extent are affected by a gradual loss of hair cells in the cochlea or neurons in the auditory (8th) nerve. The stria vascularis may also atrophy and there may be a loss of elasticity in the basilar membrane.
This usually affects the higher frequencies leading to a high frequency, bilateral symmetrical hearing loss, with a characteristic audiological appearance.
The loss of higher frequencies affects one's perception of sound and particularly speech. Many of the sounds making up consonants are of high frequency, whereas vowels tend to be lower frequency. This makes perception of speech difficult, especially in the presence of background noise. Many patients will mention this as a presenting complaint.
No treatment is available except hearing aids, however, these do not necessarily specifically amplify the high frequencies, sufferers can find these quite difficult to use.

Noise induced hearing loss (NIHL)

Noise levels above a certain threshold and duration lead to first reversible and subsequently permanent injury to the cochlear hair cells. Duration of the noise exposure is important as well as absolute volume. Continued exposure to sounds above 85 dB in volume is likely to lead to damage. Initially there is a reversible hearing loss on short exposure to noise, known as temporary threshold shift, on prolonged, repeated exposure, this will become irreversible. The outer hair cells of the cochlea are characteristically damaged. There may be a genetic predisposition to NIHL and older people are more likely to be affected.

Recently, industrial noise related deafness has been much better recognised and ear defenders are compulsory in noisy areas of factories but twenty to thirty years ago, workers were often exposed to quite high volumes without protection. Groups most affected include:

miners
factory workers, especially printing and sheet metal
armed forces, especially artillery and tanks
construction site workers - road drills etc.

Although there is considerable anxiety about the place of loud music and noise related deafness, it is generally not as loud as some of the industries mentioned above, however, headphones and Walkman's should be used with caution.

The hair cells most affected are in the area of the cochlea which deals with sound in the frequencies 3-6KHz. This gives the characteristic 4Khz notch in the audiogram that is pathognomonic of NIHL.

There is no treatment for NIHL except avoiding serious noise exposure in the first place. People at risk should always wear ear defenders, and anyone with established hearing loss should take extra care as they are at a higher risk of further damage. Companies with noisy work environments should undertake regular screening audiograms on employees.

Ototoxicity

Certain drugs are capable of damaging the cochlea and sometimes the vestibule (balance organs)

Aminoglycoside antibiotics: Vancomycin, neomycin, and tobramycin are mostly toxic to the cochlea. Gentamicin and streptomycin (an older drug, once commonly used in TB treatment) are more toxic to the vestibule.
Loop Diuretics such as frusemide
Chemotherapy for Cancer including Cisplatin
Antimalarials, chloroquine, quinine
Although Aspirin may cause tinnitus, especially in overuse, it less commonly leads to hearing loss.

Usually the patient will notice tinnitus as a first symptom and this should warn medical staff in patients who are on potentially ototoxic drugs. Hearing should be monitored, particularly if the risk is thought to be high, ideally with an audiogram prior to starting therapy. Treatment is cessation of drugs, where possible, but if the loss is permanent, a hearing aid may be needed. The audiogram may demonstrate a high tone loss.

Systemic disease

A variety of systemic diseases may cause a sensorineural hearing loss:

Hypothyroidism
Diabetes
Sarcoidosis
Vitamin B deficiency
Wegner's Granulomatosis (mixed conductive and sensorineural)
Cogan's syndrome
Leukaemia

Acoustic Neuromas

Unexplained unilateral sensorineural hearing loss must be investigated for an acoustic neuroma

These rare tumors usually present with unilateral sensorineural hearing loss. The importance of early detection is that surgery to remove a small tumour is much easier and less likely to lead to complications.

Although traditionally called acoustic neuroma, these tumours usually arise on the superior bundle of the vestibular nerve and are in fact schwannomas not neuromas. They are usually sporadic as a result of a specific mutation, but in Neurofibromatosis type 2 (NF2) they are characteristically bilateral. They affect men and women equally and generally in the age 30-60. They are generally very slow growing. Although benign tumours, they may cause life threatening problems because of their proximity to the brainstem.

Audiological features
The commonest feature is hearing loss, which may be any frequency but sensorineural. As the loss is specifically neural, there is early loss of speech discrimination, worse than might be suggested by the audiogram. Tinnitus is often a feature and is unilateral. Vertigo is an unusual feature. As the tumour grows so slowly, the CNS compensated for the gradual loss of function on the affected vestibule, and the patient is not usually aware of any loss of function.

Neurological features
As these lesions are generally detected earlier nowadays, neurological features are rare. Prior to widespread CT and MRI scanning, these features were commoner.
As the tumour enlarges it affects the Trigeminal nerve first. The most sensitive test of this is the loss of corneal or blink reflex.
Gradual enlargement may affect the facial nerve, although this is generally a very late sign.
Increasing tumour bulk may lead to symptoms of raised intracranial pressure with papillodema, pressure on the brainstem may lead to ataxia, vertigo and nystagmus as well as other cerebellar signs.

Investigation
The single best investigation for acoustic neuromas is an MRI scan of the internal auditory meatus and brainstem with Gadolinium (a paramagnetic enhancing agent usually referred to as 'contrast'). Very small lesions may be seen in the internal auditory meatus where the lesion classically arises, and extension into, and compression of the brainstem may also be assessed. With very good scans, the facial nerve can occasionally be seen in the IAM. (put image here)

Treatment
Untreated, these tumours grow slowly. In the very elderly, it may be appropriate to leave them alone. (expectant treatment).
The traditional treatment is surgical removal, which is usually a combined ENT / Neurosurgical procedure. Complications include facial paralysis, CSF leak, severe tinnitus and occasionally infarct and even death. Smaller tumours may ne removed with an attempt to preserve remaining hearing on the affected side. Usually, the hearing on the affected side is lost.
More recently, stereotactic radiotherapy ('the Gamma Knife') has been used to treat these lesions. Although sounding initially attractive, this treatment is not without complications and facial paralysis and other complications may also occur. The place of radiotherapy in the treatment of acoustic neuroma remains unclear at present.

Yahoo search results on 'acoustic neuroma' - patient information sites etc.

Tinnitus

This is the sensation of noise in the ear, occasionally heard in the head in general. Not included are auditory hallucinations of psychosis or the occasional tuneful sounds associated with temporal lobe epilepsy. Equally an audible vascular bruit is not tinnitus.

The noise may be rushing or ringing at any pitch although higher pitch is commoner. There is usually an association with hearing loss although not in all cases. Most people experience intermittent tinnitus at some stage in their lives, it is only when it is persistent and troublesome that it presents to the ENT surgeon. Tinnitus is more likely to be troublesome in the presence of Meniere's disease, presbyacuisis or noise induced deafness (particularly where there is a legal claim pending). The symptoms are worst when all is quiet, and usually at night. Occasionally patients will be kept awake at night.

Unilateral tinnitus may be the presenting symptom of an acoustic neuroma .

Pulsatile tinnitus is often the abnormal perception of the sound of blood flowing through the carotid syphon (especially if atheromatous) but it may represent a rare vascular tumour of the middle ear called a glomus tumour or equally rarely an arterio-venous malformation in or around around the temporal bone

Severe tinnitus is associated with affective disorder in 40%. Patients may rarely be suicidal.

Management of tinnitus

Thorough examination and audiometery is indicated. Any underlying cause should be treated. If noise exposure is current, advice should be given.

Most patients are happy to be reassured that tinnitus is not the first sign of a brain tumour and learn to put up with it. There is no magic cure for tinnitus. No drug treatment of surgery is usually effective. Wild claims of benefit have been made for the herbal remedy Gingko Biloba, but there is, predictably, no convincing evidence to support these. Alternative treatments such as hypnotherapy or acupuncture have no proven value, but if they help the individual patient, they are generally harmless, other than to the wallet.

Treatment of more severe cases involves tinnitus counseling which effectively helps patients learn to cope. White noise generators may help when placed near the bed at night, and tinnitus retraining therapy and maskers may be used. All of these techniques essentially help the patient learn to cope themselves.

Related links of interest

British Tinnitus Association

Tinnitus Retraining Therapy Site

Association for Tinnitus Research

Treatment of Hearing loss

Often, mild hearing loss needs no treatment other than making the patients friends and family aware of the problem.

Conductive

Conductive hearing loss may be treated with hearing aids, which are usually very effective, or by surgery in appropriate cases. Examples of conducive losses amenable to surgical help include:

Glue ear (otitis media with effusion / OME)
Very large perforations
Ossicular chain damage or loss (including traumatic dislocation)
Otosclerosis

All surgery has potential complications including deafness. The more complex the procedure the higher the risks are. Some people may prefer to avoid these risks and use a hearing aid. Some may find hearing aids intolerable and associate them with the elderly and infirm.

Sensorineural

The treatment of sensorineural loss, other than avoiding the cause such as NIHL and ototoxic drugs, is basically the provision of hearing aids. These may not work as effectively as predicted because of the loss of discrimination associated with sensorineural loss, but surgery is not an option. The only exception to this rule is in profound hearing loss, where cochlear implantation may be an option. In this procedure, an electrode array is implanted into the cochlea to allow direct electrical stimulation of the cochlear nerve. In this way, many children deafened by meningitis and other causes have become able to hear and adopt near normal lifestyles again.

Sensorineural

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