Hearing loss affects most individuals at some point in their lives. One in five people in the UK have hearing difficulties and minor hearing loss is common after the age of 20 years. It can be temporary, such as when suffering from ear infections, or a more permanent sensorineural loss of old age.
1. Classifying hearing loss
Hearing loss is classified as sensorineural, conductive or both (mixed). Sensorineural loss is usually due to inner ear (sensory) or auditory nerve (neural) lesions.
The distinction is important as some forms of sensory hearing loss are reversible, unlike neural hearing loss.
Conductive hearing loss occurs when sound is unable to reach the inner ear through mechanical problems of the outer or middle ear, for example, because of impacted wax.
Mixed hearing loss can result from severe head injury, chronic infection or various genetic syndromes.
Potential causes of tinnitus and hearing loss include:
Hearing loss can be congenital or acquired. Ear infections are the most common cause of acquired conductive hearing loss in children.
Acute or chronic otitis media sequelae can sometimes lead to permanent problems, especially if a cholesteatoma develops.
Most acute infections lead to secretory otitis media (SOM), which can last for a few weeks. Eustachian tube dysfunction can contribute to SOM. Other infections include measles, mumps, meningitis, purulent labyrinthitis and scarlet fever.
Otosclerosis is hereditary and causes conductive hearing loss. It usually manifests in late adolescence or early adulthood. Often, other family members are affected and a family history would suggest the diagnosis.
Acoustic trauma, such as sudden loud noises, may be associated with tinnitus. Chronic noise induced hearing loss (rock concerts, earphones) occurs at noise exposure >85 decibels.
Barotrauma results from sudden changes in pressure. Head trauma can lead to perforation of the eardrum or fracture of the temporal bone; tumours of the ear (benign and malignant) cause unilateral hearing loss.
Presbycusis of old age results in bilateral progressive sensory hearing loss. Loss of the ability to hear high-pitched sounds makes it difficult to distinguish speech.
Autoimmune disorders such as rheumatoid arthritis and systemic lupus erythematosus have been linked to hearing problems. Such loss can be progressive and affect both ears.
Meniere's disease is usually unilateral and characterised by vertigo and tinnitus. Tinnitus can be distressing and often requires referral for masking or psychological therapies.
Some drugs are implicated in hearing loss, particularly at higher doses. Predisposition to damage from these can have a hereditary component. Aminoglycosides, vancomycin, quinine and some cancer drugs such as cisplatin are recognised causative agents.
Congenital causes include ear defects present at birth, genetic syndromes (such as neurofibromatosis) or in utero infections (toxoplasmosis, cytomegalovirus, rubella or herpes). Maternal ingestion of ototoxic drugs has also been implicated. Anoxia can be a cause of hearing loss, as can rhesus incompatibility.
Assessment should begin at birth by noticing if the infant startles to loud noises. This is because hearing loss in early childhood can result in profound impairment in receptive and expressive language skills.
The severity of limitation will depend on the nature of the deficit and the age at which it first occurred. Around 840 babies are born with significant deafness every year in the UK.
Screening tests are therefore very important at birth and include the otoacoustic emissions test, which will pick up an echo if the cochlea is functioning normally. Other diagnostic tests will be done if there is concern.
In older individuals, past medical history should always look to establish any causative factors such as exposure to loud noise, trauma, autoimmune or hereditary causes. Drug history is also very important to note.
Physical examination will exclude obstruction, otitis media, congenital malformations or cholesteatoma.
A neurological examination should be done to assess cranial nerves as well as vestibular and cerebellar assessments to exclude tumours. Weber's and Rinne's tests involve the use of a tuning fork and can differentiate between conductive and sensorineural hearing loss.
In cases of uncertainty or in the presence of neurological findings or unilateral sensorineural loss, refer for further investigations; these can include audiological assessments, CT or MRI.
Audiometry will quantify hearing loss while tympanometry measures the level of impedance of the middle ear (such as in effusions).
This largely depends on the causes of hearing loss. For example, ototoxic drug use should be carefully monitored (through peak and trough drug levels). ENT specialists can drain fluid from the middle ear and remove benign tumours, polyps and adenoids. Hearing loss from autoimmune disorders sometimes responds to steroids. Otosclerosis can be corrected through surgery.
Hearing aids can help some people but those with high frequency hearing loss do not respond to simple amplification as speech remains unclear. They need selective amplification of higher frequencies.
Cochlear implants, although uncommon, can dramatically improve quality of life in many profoundly deaf patients.
They deliver electrical signals directly into the auditory nerve through electrodes implanted in the cochlea.
Speech and language therapists also have an important part to play, particularly for children and young adults. Sign language is key to their psychological development.
- Dr Aziz is a GP in Bristol
- Bauer C, Jenkins H. Otologic symptoms and syndromes. In: Cummings C, Haughey B, Thomas JR et al (eds). Otolaryngology: Head and Neck Surgery (fifth edition). Philadelphia, Mosby, 2010.
- NHS Newborn Hearing Screening Programme. Aetiological investigation guidelines. January 2009. http://hearing.screening.nhs.uk/aetiologicalguidelines#fileid16577