Deafness

Attention has already been drawn to the two major categories of deafness—conductive and sensorineural. The distinction is easily made by tuning fork tests, which should never be omitted. CAUSES There is no strict order in the list featured in Table 4.1, because the frequency with which various causes of deafness occur varies from one community to another and from one age group to another.Nevertheless, some indication is given by division into ‘more common’ and ‘less common’ groups. Always try to make a diagnosis of the cause of deafness and start by deciding whether it is conductive or sensorineural. MANAGEMENT The management of a number of specific conditions will be dealt with in subsequent chapters but some general comments are appropriate. deaf child Early diagnosis of deafness in the infant is essential if irretrievable developmental delay is to be avoided.The health visitor should screen all babies at about 8 months of age and those failing a routine test must be referred to a specialist audiological centre without delay for more thorough investigation. Some babies are ‘at risk’ of deafness and are tested as soon after birth as possible.They include those affected by: 1 prematurity and low birth-weight; 2 perinatal hypoxia; 3 Rhesus disease; 4 family history of hereditary deafness; 5 intrauterine exposure to viruses such as rubella, cytomegalovirus and HIV. The testing of babies suspected or at risk of being deaf is very specialized. The mother’s assessment is very important and should always be taken seriously. She is likely to be right if she thinks her child’s hearing is not normal. Testing of ‘at risk’ babies in the neonatal period is now carried out in many centres by the recording of otoacoustic emissions (see Chapter 3). Conductive Sensorineural More common Wax Presbycusis (deafness of old age) Acute otitis media Noise-induced (prolonged exposure to high noise level, industrial deafness, chronic otitis media disco music) Barotrauma Congenital (maternal rubella, cytomegalovirus, Otosclerosis toxoplasmosis, hereditary deafness,anoxia, jaundice,congenital syphilis) Injury of the tympanic membrane Drug-induced (aminoglycoside antibiotics, aspirin, quinine, some diuretics, some beta blockers) Menière’s disease Late otosclerosis Infections (CSOM,mumps,herpes zoster, meningitis, syphilis) Less common Traumatic ossicular dislocation Acoustic neuroma Congenital atresia of the external Head injury canal Agenesis of the middle ear CNS disease (multiple sclerosis, metastases) Tumours of the middle ear Metabolic (diabetes,hypothyroidism, Paget’s disease of bone) Psychogenic Unknown aetiology Sudden sensorineural deafness Sudden sensorineural deafness is an otological emergency and should be treated as seriously as would be sudden blindness. Immediate admission to hospital should be arranged, as delay may mean permanent deafness. Sudden deafness may be unilateral or bilateral and most cases are regarded as being viral or vascular in origin. Investigation may fail to show a cause and treatment is usually with low-molecular-weight dextran, steroids and inhaled carbon dioxide. Bilateral profound deafness, especially if of sudden onset, is a devastating blow and for this reason various organizations exist to give advice and support. Vestibular Schwannoma (Acoustic neuroma) Vestibular Schwannoma is a benign tumour of the superior vestibular nerve in the internal auditory meatus or cerebello-pontine (CP) angle. It is usually unilateral, except in familial neurofibromatosis (NF2), when it may be bilat-eral. In its early stages, it causes a progressive hearing loss and some imbalance. As it enlarges, it may encroach on the trigeminal nerve in the CP angle, causing loss of corneal sensation. In its advanced stage, there is raised intracranial pressure and brain stem displacement. Early diagnosis reduces the morbidity and mortality of operations. Unilateral sensorineural deafness should always be investigated to exclude a neuroma. Audiometry will confirm the hearing loss. MR scanning will identify even small tumours with certainty (Fig. 4.1). Hearing aids In cochlear forms of sensorineural deafness, loudness recruitment is often a marked feature. This results in an intolerance of noise above a certain threshold, and makes the provision of amplification very difficult. The choice of hearing aids is now large. Most are worn behind the ear with a mould fitting into the meatus. If the mould does not fit well, oscillatory feedback will occur and the patient will not wear the aid. More sophisticated (and expensive) are the ‘all-in-the-ear’ aids, where the electronics are built into a mould made to fit the patient’s ear. They give good directional hearing and, because they are individually built, the output can bematched to the patient’s deafness. The current generation of hearing aids are digital, allowing more refinement in the sound processing and more control of the aid. A recent development has been the bone-anchored hearing aid (BAHA). A titanium screw is threaded into the temporal bone and allowed to fuse to the bone (osseo-integration). A transcutaneous abutment then allows the attachment of a special hearing aid that transmits sound directly by bone conduction to the cochlea.The main application of BAHA is to patients with no ear canal, or chronic ear disease, who are unable to wear a conventional aid and is much more effective than the old-fashioned bone conductor aid. Cochlear implants Much research has been done, both in the USA and Europe, on the implantation of electrodes into the cochlea to stimulate the auditory nerve.The apparatus consists of a microphone, an electronic sound processor and a single or multichannel electrode implanted into the cochlea. Cochlear implantation is only appropriate for the profoundly deaf. Results, particularly with an intracochlear multichannel device, can be spectacular, with some patients able to converse easily. Most patients obtain a significant improvement in their ability to communicate and implantation has been extended for use in children. It is no longer an experimental procedure but a valuable therapeutic technique. Lip-reading Instruction in lip-reading is carried out much better while usable hearing persists and should always be advised to those at risk of total or profound deafness. Electronic aids for the deaf Amplifying telephones are easily available to the deaf and telephone companies usually provide willing advice. Many modern hearing aids are fitted with a loop inductance system to make the use of telephones easier. Various computerized voice analysers that give a rapid visual display are also available, but these require the services of a skilled operator and are still in the developmental phase. Automatic voice recognition machines maytake over this role in the foreseeable future.

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