37 Hearing Loss—Acquired
Acquired hearing loss affects over 11 million people in the United Kingdom with this figure set to rise to 15.6 million by 2035 (Action on Hearing Loss). Nine hundred thousand currently have severe or profound hearing loss. It is associated with significant social isolation and, in the elderly, with cognitive decline. There are therefore significant societal implications from hearing loss.
This chapter will summarise the most common causes of acquired hearing loss and discuss the current options available for hearing rehabilitation.
Diagnosis of hearing loss is usually made using psychoacoustic techniques. Pure-tone audiometry is in widespread use and can differentiate conductive from sensorineural hearing loss. It does not, however, provide a measure of functional hearing and word (e.g., Arthur Boothroyd words) or sentence testing (e.g., Bamford Kowal Bench [BKB] or City University of New York [CUNY] Sentences) that may be used to provide additional information on functional hearing. This is important as patients often complain of distortion of hearing as well as an inability to hear adequately and it is only functional tests of hearing that will identify those with distortion. Hearing aids only amplify the existing hearing and the benefits of aiding in those with distorted hearing may be limited.
Objective measures of hearing loss may also be used in some circumstances especially to identify malingerers. These include brainstem-evoked response audiometry (BSER) and cortical-evoked response audiometry (CERA). Tympanometry has a role in confirming the presence of a tympanic membrane perforation or middle ear effusion. Otoacoustic emissions may also be helpful in differentiating neural from sensory loss and is helpful in the diagnosis of auditory neuropathy. It is also the screening test used in neonatal hearing screening.
Cross-sectional imaging has an important role to play in some patients. High-resolution computed tomography (CT) may be helpful in the investigation of conductive hearing losses. It can identify ossicular discontinuity and otosclerosis and allows assessment of the extent of cholesteatomatous disease. Magnetic resonance imaging (MRI) is also helpful in certain situations, mainly for the exclusion of intra-cranial causes of sensorineural hearing loss such as vestibular schwannoma.
Causes of acquired hearing loss can be divided into conductive and sensorineural. Conductive hearing loss results from impairment of the passage of sound from the external environment to the cochlea. This can result from disease of the external ear, tympanic membrane or middle ear. Sensorineural hearing loss results from disease of the cochlea, cochlear nerve or central auditory pathways. Table 37.1 summarises the most common causes of acquired conductive hearing loss. Table 37.2 summarises the most common causes of acquired sensorineural hearing loss.
37.4 Conductive Hearing Loss
Many forms of conductive hearing loss can be addressed with surgery to the ossicular chain although traditional hearing aids and implantable bone conduction hearing aids may also be options.
37.5 External Auditory Canal
• Foreign bodies and wax are usually easily removed with microsuction. Syringing has fallen out of fashion in recent years mainly because of the risk of perforation and trauma to the external ear canal.
Table 37.1 Most common causes of acquired conductive hearing loss
External ear canal
Stenosing otitis externa
Exostoses and osteomas
Fixation, e.g., otosclerosis
Erosion, e.g., cholesteatoma
Subluxation and fracture, e.g., trauma
Table 37.2 Most common causes of acquired sensorineural hearing loss
Ramsay Hunt syndrome, syphilis, meningitis
Cerebrovascular accident, sickle cell disease
Ménière’s disease, autoimmune disease, e.g., rheumatoid arthritis, sarcoidosis
Noise, temporal bone fracture
• Stenosing otitis externa results in progressive inflammatory narrowing of the external auditory canal with eventual formation of a deep ear canal fibrous plug. The underlying tympanic membrane is usually normal. Once the otitis externa has burnt out, surgical correction may be considered in order to restore hearing although stenosis recurs in up to 60% of cases. The fibrous plug is removed down to the healthy tympanic membrane. A bony canalplasty is usually carried out and the deep ear canal can then be grafted using a split-skin graft. Alternatively, a number of different implantable bone conduction hearing aids (IBCHAs) can be used and these provide excellent hearing outcomes albeit with the inconvenience of having to wear an aid.
• Exostoses result from repeated prolonged exposure to cold water. This causes an hyperostotic reaction resulting in formation of several bony swellings in the deep ear canal. It is most commonly seen in surfers. When small, they do not cause any problems, but large ones can completely occlude the external auditory canal. Progression can be stopped through appropriate ear plugging during exposure to cold water. This may avoid the need for intervention. Large ones can be removed by carrying out a bony canalplasty.
• Osteomas are benign neoplasms of the bony external auditory canal. They are solitary, have a pedunculated base, and usually arise at the bony margin of the tympanic ring. These features differentiate them from exostoses. In the same way as exostoses, they can occlude the external auditory canal when large. It is usually a straightforward matter to fracture the osteoma at its base and remove it although formal canalplasty may be required in some cases.
37.6 Tympanic Membrane
Perforations of the tympanic membrane do not cause conductive hearing loss when small but large ones often do. While the primary aim of tympanoplasty is to close the tympanic membrane, a secondary effect in those with an associated conductive hearing loss is often improvement in hearing.