La explotación de la quina

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DEAFNESS Michael Gleeson

Deafness is rarely total or complete. The term ‘hearing loss’ is a better term to use as it implies that there may be degrees of deafness. Hearing loss is an extremely common problem, and constitutes one of the major handicaps affecting mankind. Most of us will have experienced a temporary hearing loss in one or other ear at some time, perhaps when flying or associated with a cold, and should be able to appreciate how incapacitating permanent and more severe loss of hearing must be. In fact, almost 60 per cent of the population will have acquired a significant degree of hearing loss by the time they retire from full-time employment.

From a clinical standpoint, three types of hearing loss are recognized, namely conductive, sensorineural and mixed.

• Conductive hearing loss: this is caused by lesions in the external and/or middle ear that attenuate or prevent sound reaching the cochlea.

• Sensorineural hearing loss: this is caused by lesions within the cochlea or affecting the auditory nerve and/or higher pathways.

• Mixed hearing loss: this is caused by a combination of conductive and sensorineural elements.

Hearing tests

These tests are undertaken to determine the nature and severity of hearing loss. Both psycho-acoustic and objec-tive tests have been devised and are employed in clinical practice.

Voice tests

An initial assessment of hearing loss can be gained by occlusion of the contralateral ear while speaking or whispering into the ipsilateral ear. The patient should be told to repeat exactly what the examiner says, and be positioned so that they cannot see the examiner’s lips.

Anyone with normal hearing will be able to hear a whispered voice at a distance of 60 cm (2 feet). Hearing in the contralateral ear is usually masked by gentle pressure on the tragus, or by holding paper over the ear and scratching it when speaking. An alternative and better method of masking the non-test ear is by use of a Barany box; this is a sound-generating device that is inserted into

the contralateral ear canal and emits a loud noise while testing the other ear. More accurate measures of the spoken voice can be obtained with sound pressure meters.

Tuning-fork tests

With these simple, chair-side tests, it is possible to distin-guish between conductive and sensorineural hearing losses. Only 256 cycles per second (cps) or 512 cps tuning forks should be used. Lower frequency tuning forks are appropriate for vibration sense tests only.

The Rinne test

The tuning fork is struck and its base held firmly on the patient’s mastoid process until they no longer hear the tone. The fork is then rapidly transferred so that the vibrating forks are close to the external auditory meatus.

If the patient continues to hear the sound, it is considered that they hear better by air conduction than by bone conduction – a positive test result. In fact, in patients with normal middle-ear function the sound is usually perceived as being much louder. Patients with either normal hearing acuity or with a sensorineural hearing loss perceive the tuning fork better by air conduction than by bone conduction. Conversely, patients with conductive losses hear the tuning fork better by bone conduction than air conduction – a negative test result.

The Weber test

In this test, the tuning fork is placed in the middle of the forehead or on the vertex, and the patient is asked to signify in which ear they hear the sound louder. In the Weber test, the sound is either heard better by one ear (in other words, it lateralizes), or it is heard equally by both ears. The sound lateralizes to the ear with the better hearing in sensorineural hearing loss, or to the ear with the greater conductive hearing loss in patients with conductive hearing losses. The normal response is to hear the sound equally in both ears, but this result can also be obtained in patients with equal sensorineural or conduc-tive hearing loss.

The absolute bone-conduction test

In this test, an assessment is made of the patient’s ability to hear by bone conduction. This is a measure of sensorineural deafness, and the patient’s response is compared with the examiner’s perception of the tone. If the examiner has roughly normal hearing, the patient ought to hear a tuning fork placed on their mastoid as long as the examiner does. If they hear it for less time, it is considered that their bone conduction is diminished and they have worse hearing than the examiner, probably a sensorineural hearing loss.

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Audiometry Pure-tone audiometry

A pure-tone audiometer produces tones of varying inten-sity (0–120 dB) and frequency (125–8000 Hz). The test is performed with the patient wearing earphones, usually but not always in a sound-proofed environment. Test sounds at different intensities and frequencies are intro-duced via the earphones, and patients are asked to indicate when they hear the sound. Threshold values at each frequency are determined and plotted on a graph – an audiogram (Fig. D.1). Normal thresholds have been estab-lished by the National Physics Laboratory, and young adults should have threshold values across the test range of 0–10  dB, with 0  dB being the sound pressure level considered to be threshold for 18-year-olds.

audiogram, where the patient has to respond to a list of test words played at threshold levels through earphones.

Either a graph can be made of the patient’s speech responses at each test level, or a simple raw speech discrimination score can be recorded. The threshold level at which approximately 50 per cent of the words are inter-preted correctly (the half-peak level) is about equivalent to the pure-tone average. A difference between the half-peak level of a speech audiogram and the pure-tone average audiogram is indicative of malingering. Patients with pure conductive losses achieve 100 per cent discrimina-tion at an elevated sound presentadiscrimina-tion level, and sustain this increased sound pressure level. Conversely, patients with sensorineural hearing losses rarely achieve 100 per cent discrimination, and with increased sound pressure levels the scores deteriorate – a phenomenon known as

‘roll-over’.

Tympanometry

Tympanometers measure middle-ear compliance. Sound is injected into the ear canal, and the reflected sound level is measured while the atmospheric pressure of the ear canal is varied. The reciprocal value of the reflected sound – the compliance – is plotted against the atmos-pheric pressure. The compliance of the middle ear is greatest when the external ear canal pressure is the same as that in the middle ear. This test can diagnose middle-ear effusions, ossicular disruptions or discontinuity, and Eustachian tube dysfunction. Low compliance levels are seen in severe otosclerotic fixation of the stapes footplate.

Changes in middle-ear compliance produced by stape-dius muscle contraction can also be measured by inject-ing high-intensity sound (threshold 180 dB) to elicit the stapedial reflex. An absence of the reflex or abnormal decay of reflex activity is of diagnostic importance in otosclerosis, ossicular discontinuity and retrocochlear hearing loss.

Evoked response audiometry

Sound transduction into neural activity can be detected throughout the auditory pathway. In the cochlea, contrac-tion of the outer hair cells produces echoes that can be heard by sensitive microphones; depolarization of the first-order neurones can be recorded by electrocochleography and the passage of neural flux in the auditory pathways documented by brainstem and cortical techniques. All of these techniques have specific indications, but find univer-sal use for screening neonates for hearing loss, detecting non-organic hearing loss in medicolegal problems, and investigating patients with endolymphatic hydrops.

10 0 10 20 30 40 50 60 70 80 90 100

Hearing loss in decibels

125 250 500 1000 2000 4000 8000 12000

Frequency in cycles per second Figure D.1 Audiogram showing hearing that is within

‘normal limits’. It is conventional to represent hearing by air conduction in the right ear by O–O, and in the left ear by X–X.

Bone conduction is considered to be equivalent to cochlear function as it bypasses the middle-ear conduc-tion mechanism. To obtain bone conducconduc-tion, a vibrating disk is applied to the patient’s mastoid process. The test is then carried out in the same manner as for air conduc-tion, and the auditory thresholds are obtained and plotted on the audiogram. In this way, it can be seen whether bone conduction is better than air conduction (conductive deafness), or if bone conduction and air conduction are roughly equal (normal or sensorineural deafness).

Speech audiometry

It is possible for a patient to produce a normal pure-tone audiogram yet be unable to interpret or discriminate speech. A more discriminatory test of hearing is a speech

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Hearing tests in children

Deafness should be diagnosed in infants as early as possible. The earlier that deafness is diagnosed, the more chance there is of the child developing normal language skills and not falling behind their peer group from an educational standpoint. Every child born in the UK has a hearing test by specially trained nurses at 6 weeks and at the end of the first year of life. Children at particular risk of hearing loss (e.g. those born to deaf parents), premature births requiring intensive care, and infants with abnormal facies, etc. are tested within days of birth or discharge from hospital. Where the nurse does not receive an unambiguous response indicating normal hearing from simple clinical tests, the child is referred to a special children’s speech and hearing clinic. There, further clinical tests are undertaken, which may include evoked response audiometry.

If a child is found to be deaf, special education is set in hand at a very early age and amplification devices are fitted to the child, depending on the severity of the deafness. Those found to be profoundly deaf are consid-ered for cochlear implantation.

Conductive deafness

The common causes of conductive deafness are listed in Box D.1.

Conductive deafness is often less severe than senso-rineural deafness. Complete disruption of the sound-transmitting mechanism imparts a 60  dB hearing loss, while a simple perforation inflicts a hearing loss of 25–30  dB. Many of these conductive hearing losses are amenable to surgical correction (e.g. otosclerosis, middle-ear effusions or perforations), and some can be cured by medication (e.g. acute otitis media). Others can be overcome by hearing aids.

Congenital syndromes

There are a number of congenital syndromes associated with deafness, and most are sensorineural in nature.

Where there is a conductive element to the hearing loss, it is often associated with a cochlear abnormality as well as resulting in a mixed hearing loss. It is quite impossible to list all the possible combinations of congenital abnormalities, but the golden rule is that if one abnormality is observed, a careful search for others must be made and that, during this search, deafness must never be forgotten. Some of the more common congenital syndromes associated with hearing loss are listed below.

Goldenhar’s syndrome

The anomalies characteristically present in this mal -development of the first and second branchial arches are microtia, total atresia of the external auditory canal, ossicular abnormalities, absent middle-ear muscles and anomalous facial nerve pathway. Abnormalities of the inner ear may be present, as well as hemifacial microsmia (Fig. D.2).

Treacher Collins syndrome

This comprises micrognathia, depressed malar bones, eyes sloping downwards and outwards with notched lower lids, ptosis of the auricles and middle-ear abnormalities with deformed ossicles (Fig. D.3).

Congenital lesions

Atresia of the external meatus and middle ear usually with microtia (see Fig. D.2)

Atresia associated with other facial defects Middle-ear deformities

● Some syndromes (frequently associated with sensorineural loss in addition to the conductive loss)

•Mandibulofacial dysostosis (Treacher Collins syndrome)

•Crouzon’s deformity

•Marfan’s syndrome

•Klippel–Feil syndrome

•Trisomy D and E

•Cretinism

•Cleft palate

•Submucous cleft palate

•Osteogenesis imperfecta (van der Hoeve–de Kleyn triad)

•Thalidomide

•Rubella

External auditory meatus

● Wax

● Foreign bodies

● Otitis externa

● Exostoses (diver’s ear, wet ear) Middle-ear lesions

● Trauma

● Blood

● Ossicular disruption

● Perforated tympanic membrane

● Acute otitis media

● Eustachian malfunction

•Atelectasis of middle ear

•Serous otitis (‘glue ear’)

● Otitic barotrauma

● Chronic otitis media

● Haemotympanum

● Malignant disease

● Glomus tumour

● Otosclerosis

Box D.1 The causes of conductive deafness

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Crouzon’s deformity

Crouzon’s syndrome is a craniofacial dysostosis charac-terized by exophthalmos, a divergent squint, hypoplastic maxillae, a short upper lip, hypertelorism, a beak-shaped nose and deafness caused by atresia and middle-ear abnormalities.

Marfan’s syndrome

This comprises an inherited collagen disorder, abnormally long extremities, subluxation of the lens, cardiovascular abnormalities and deafness. The auricles are very large in this condition, and the cartilaginous canals tend to collapse.

Klippel–Feil syndrome

This is a syndrome in which there are malformed cervical vertebrae and a webbed neck in association with hearing loss caused by ankylosis of the ossicles. Some patients also have rudimentary inner ears.

Trisomy D and E

Patients with this condition have low-set ears, preauri-cular tags, atresia of the external auditory canals and an absence of the middle-ear cleft.

Osteogenesis imperfecta

Sometimes known as the van der Hoeve’s syndrome, the classical triad is deafness caused by stapedial fixation and incudo-stapedial fragility, blue sclera and fragile bones. It is fortunately an uncommon condition, with a frequency of 2–3 per 100 000 population.

Cleft palate

Cleft palate is one of the most common congenital deform-ities, with a frequency of about 1 in 1000. It is also a cause of deafness. The palatal muscles (tensor palati and levator palati) play an important part in Eustachian tube opening and closure. Nearly every child with a cleft palate has a middle-ear effusion, and some go on to develop atalectasis Figure D.2 Atresia of the right ear, showing an absent external

auditory meatus and deformed auricle.

Figure D.3 Treacher–Collins syndrome, showing the typical appearance of the eye, micrognathia, depressed malar bone and ptosis of the ear.

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z of the middle-ear cleft. Closure of the palatal defect does

not influence Eustachian tube function. Submucous clefts of the palate in which there is a deficiency of the muscular layer are equally disruptive to Eustachian tube function.

Some of these children are helped by reconstructive surgery. This can be a difficult condition to recognize but, in a few, a bifid uvula may be present and draw attention to the abnormality (Fig. D.4).

Otitis media with effusion (secretory otitis media,

‘glue ear’)

This is an extremely common condition and is present in 4 per cent of all children aged between 5 and 15 years.

This means that almost every classroom in the country will contain one child with a temporary hearing loss caused by ‘glue ear’. The resulting hearing loss is variable, but may be sufficient to impair education. Fairly typical changes occur in the eardrum, which becomes retracted and develops a yellowish glaze. Occasionally, fluid levels and bubbles can be seen through the eardrum, but in other instances there may be no observable clinical signs. The diagnosis is made by tympanometry, where a flat compli-ance curve is recorded. In adults, otitis media with effusion may be the first sign of Eustachian tube obstruction by a nasopharyngeal carcinoma. Although less common among Europeans, this condition is of very definite clinical signif-icance in the Chinese, where nasopharyngeal carcinoma is the most common head and neck tumour. Drainage of the effusions and the insertion of grommets (ventilation tubes) restores hearing.

Acute otitis media

This is a common viral or bacterial infective disorder of childhood caused by Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and, less frequently, Streptococcus pyogenes or Staphylococcus aureus. Acute otitis media often accompanies or compli-cates upper respiratory tract infections. The child becomes unwell and pyrexial, and complains of a hearing loss in the affected ear and increasing earache. Occasion-ally, instead of complaining of earache, a child may complain of abdominal pain. Eventually, the eardrum ruptures to release pus that has accumulated in the middle-ear cleft. Pain diminishes rapidly once the pus has drained, as do any toxic symptoms and signs. Over the course of the next few days, the infection resolves and the ruptured eardrum seals spontaneously in most cases. There is a considerable dichotomy of opinion about the value of antibiotics in the management of this condition. One body of opinion suggests that it can be managed just as successfully by symptomatic treatment with analgesics, while others feel that antibiotics should always be prescribed.

Chronic otitis media

Two types of chronic otitis media are recognized, tubo-tympanic and attico-antral disease. Tubo-tympanic disease is characterized by a persistent central perfora-tion, while attico-antral disease is associated with Figure D.4 Submucous cleft palate with the deeply bifid uvula

typical of this rare condition.

Other syndromes associated with hearing loss

The hearing losses found in these syndromes are often predominantly sensorineural, with relatively minor conductive elements. Examples are Pendred’s syndrome, in which hearing loss is associated with thyroid deficiency, rubella infection and thalidomide toxicity.

Abnormalities of the external auditory canal

Diseases of the external auditory meatus rarely cause deafness, as hearing is retained while there is still the smallest airway past the obstruction to the tympanic membrane. However, sudden deafness can develop when wax becomes impacted or wet, when it expands and closes the canal. Similarly, the oedema associated with otitis externa can also cause occlusion of the ear canal and a conductive hearing loss.

Middle-ear causes of hearing loss

Most of these are easily identified by a thorough and careful otoscopic examination.

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ingrowth of skin from the attic or posteromarginal region of the tympanic membrane into the mastoid antrum, mastoid and middle ear – cholesteatoma. Both groups of patients develop hearing loss in the affected ear and are subject to chronic discharge. In the case of tubo-tympanic disease, this discharge is mucoid and not particularly offensive. By contrast, patients with attico-antral disease have a watery and offensive discharge.

Both conditions are potentially dangerous, as uncon-trolled infection may spread to cause meningitis, brain abscess and facial palsy. Persistent perforations can often be repaired surgically, but those which cannot should be kept dry and free from water contamination. Episodes of infection are treated with topical antibiotics. Attico-antral disease almost always requires surgical treatment in the form of a mastoid exploration. Some small cholesteatomas can be managed by suction clearance on an intermittent basis, but these cases are relatively rare.

Otosclerosis

This is a form of deafness caused by fixation of the stapes by the development of new bone around its footplate.

It tends to affect young adults, and is a progressive form of deafness that increases as the footplate becomes more and more fixed. In females, the deafness is often made worse by pregnancy. Pure-tone audiometry demonstrates a conductive loss often with an increased loss at 2 kHz, the so-called ‘Carhart’s notch’. Treatment of this condition is determined by the degree of hearing loss it inflicts, the likely benefit derivable from surgical intervention and the patient’s wishes. Oral fluoride therapy can retard progres-sion. Those with significant hearing loss will certainly benefit from a hearing aid, and some from removal of the stapes and replacement by a prosthesis (stapedectomy).

It tends to affect young adults, and is a progressive form of deafness that increases as the footplate becomes more and more fixed. In females, the deafness is often made worse by pregnancy. Pure-tone audiometry demonstrates a conductive loss often with an increased loss at 2 kHz, the so-called ‘Carhart’s notch’. Treatment of this condition is determined by the degree of hearing loss it inflicts, the likely benefit derivable from surgical intervention and the patient’s wishes. Oral fluoride therapy can retard progres-sion. Those with significant hearing loss will certainly benefit from a hearing aid, and some from removal of the stapes and replacement by a prosthesis (stapedectomy).

In document LA MISIÓN CAPUCHINA EN EL CAQUETÁ Y EL PUTUMAYO 1893-1929 (página 32-35)