Medicine – Causes of Deafness

Deafness, or hearing loss, can be broadly divided into conductive hearing loss and sensorineural hearing loss. Conductive hearing loss occurs when sound cannot be transmitted efficiently through the external or middle ear, whereas sensorineural hearing loss results from damage to the cochlea, the vestibulocochlear nerve, or central auditory pathways.

An asterisk (*) below signifies a common cause.

1. Conductive Hearing Loss

Conductive hearing loss occurs when sound transmission through the external auditory canal, tympanic membrane, or middle-ear ossicles is impaired.

The cochlea and auditory nerve may remain functionally intact.

Typical causes include ear wax and middle-ear disease.

2. Ear Wax*

Impacted cerumen, or ear wax, is a common and usually reversible cause of conductive hearing loss.

Wax may obstruct the external auditory canal and prevent sound waves from reaching the tympanic membrane effectively.

Patients may complain of:

Reduced hearing.

Blocked-ear sensation.

Tinnitus.

Occasionally discomfort may occur.

Removal of the impacted wax usually restores hearing if no additional pathology is present.

3. Middle-Ear Disease*

Middle-ear disease is another common cause of conductive hearing loss.

Sound transmission may be impaired by fluid, infection, tympanic membrane abnormalities, or ossicular dysfunction.

Important examples include:

Otitis media.

Otitis media with effusion, or glue ear.

Tympanic membrane perforation.

Cholesteatoma.

Ossicular fixation or disruption.

The exact degree of hearing loss depends on the extent of mechanical impairment.

4. Sensorineural Hearing Loss

Sensorineural hearing loss results from damage to the inner ear, particularly the cochlea, or from dysfunction of the vestibulocochlear nerve and central auditory pathways.

Unlike many conductive causes, sensorineural hearing loss is often permanent.

It may be divided broadly into:

Cochlear causes.

Nerve or retrocochlear causes.

Congenital causes.

5. Cochlear Causes

Cochlear hearing loss results from damage to structures within the inner ear.

Important causes include:

Otosclerosis.

Noise-induced hearing loss.

Drug-induced ototoxicity.

Ménière disease.

Paget disease.

6. Otosclerosis*

Otosclerosis is caused by abnormal bone remodelling around the stapes and otic capsule.

Classically, fixation of the stapes footplate causes conductive hearing loss rather than purely sensorineural hearing loss.

However, if the disease extends into the cochlea, a sensorineural component may develop.

Therefore, although older notes may place otosclerosis under cochlear sensorineural causes, the classic presentation is:

Stapes fixation → conductive hearing loss.

7. Noise-Induced Hearing Loss*

Noise-induced hearing loss is a common cause of sensorineural deafness.

Prolonged or repeated exposure to loud noise damages cochlear hair cells.

Examples include:

Industrial noise.

Loud music.

Firearms.

Heavy machinery.

The hearing loss is usually bilateral and commonly affects high frequencies first.

8. Drug-Induced Hearing Loss

A number of drugs and toxins are ototoxic and may damage the cochlea or vestibular apparatus.

Important examples include:

Aminoglycoside antibiotics, such as gentamicin.

Loop diuretics, such as furosemide.

Certain chemotherapy drugs, especially cisplatin.

The original note also lists lead, which is better considered a toxic heavy-metal exposure rather than a drug.

9. Aminoglycosides

Aminoglycosides can damage cochlear and vestibular hair cells.

Examples include:

Gentamicin.

Amikacin.

Streptomycin.

Risk increases with higher cumulative exposure, renal impairment, and concurrent use of other ototoxic drugs.

Hearing loss may be permanent.

10. Furosemide

Furosemide is a loop diuretic that can cause ototoxicity, particularly when given in high doses or rapidly intravenously.

The risk may increase when combined with other ototoxic medications.

Hearing impairment may be reversible or permanent depending on severity.

11. Lead Exposure

Lead toxicity can damage the nervous system and may contribute to hearing impairment.

Lead is therefore best remembered as a toxic environmental cause rather than a conventional drug-induced cause.

12. Ménière Disease

Ménière disease causes fluctuating sensorineural hearing loss due to abnormal inner-ear fluid regulation, classically associated with endolymphatic hydrops.

The characteristic clinical combination is:

Episodic vertigo.

Fluctuating sensorineural hearing loss.

Tinnitus.

Aural fullness.

Hearing loss may become progressively permanent after repeated attacks.

13. Paget Disease

Paget disease of bone can involve the skull and temporal bone.

Abnormal bone remodelling may interfere with the auditory apparatus and produce:

Conductive hearing loss.

Sensorineural hearing loss.

or

Mixed hearing loss.

Therefore, hearing impairment in Paget disease is not exclusively cochlear.

14. Nerve or Retrocochlear Causes

Hearing loss may also result from damage to the vestibulocochlear nerve, CN VIII, or nearby central auditory pathways.

Important causes include:

Vestibular schwannoma.

Head trauma.

Meningitis.

15. Acoustic Neuroma

The traditional term acoustic neuroma usually refers to a vestibular schwannoma.

This is a benign tumour arising from Schwann cells, most commonly from the vestibular division of cranial nerve VIII.

A typical presentation is:

Progressive unilateral sensorineural hearing loss.

Unilateral tinnitus.

Imbalance.

Large tumours may also compress neighbouring cranial nerves or the brainstem.

16. Head Trauma

Head trauma can cause hearing loss by damaging:

The cochlea.

The vestibulocochlear nerve.

The temporal bone.

Central auditory pathways.

Temporal bone fractures may produce conductive, sensorineural, or mixed hearing loss depending on the structures damaged.

17. Meningitis

Meningitis is an important cause of acquired sensorineural hearing loss.

Inflammation can damage the cochlea or vestibulocochlear nerve.

Hearing impairment may be:

Unilateral or bilateral.

Temporary or permanent.

Bacterial meningitis is particularly important because severe hearing loss may occur after recovery from the acute infection.

18. Congenital Hearing Loss

Congenital hearing loss is present at birth or develops very early in life.

It may be caused by:

Genetic disorders.

Congenital infections.

Structural abnormalities of the inner ear.

Prematurity or perinatal complications.

Genetic causes account for a large proportion of congenital sensorineural hearing loss.

19. Congenital Infections

Important congenital infections associated with sensorineural hearing loss include:

Cytomegalovirus.

Rubella.

Other congenital infections can also cause auditory damage depending on the clinical context.

Early detection is essential because hearing impairment can significantly affect speech and language development.

20. Causes of Deafness – Note Form

Conductive hearing loss: impaired sound transmission through the external or middle ear.

Ear wax:* common, reversible obstruction of the external auditory canal.

Middle-ear disease:* otitis media, glue ear, tympanic membrane disease, cholesteatoma, or ossicular dysfunction.

Sensorineural hearing loss: damage to the cochlea, auditory nerve, or central auditory pathways.

Otosclerosis:* classically causes conductive hearing loss due to stapes fixation; cochlear involvement may add a sensorineural component.

Noise-induced hearing loss:* cochlear hair-cell damage from prolonged loud-noise exposure.

Drug-induced: aminoglycosides and furosemide are important ototoxic drugs.

Lead: toxic heavy-metal exposure that may contribute to hearing impairment.

Ménière disease: vertigo + fluctuating sensorineural hearing loss + tinnitus + aural fullness.

Paget disease: may produce conductive, sensorineural, or mixed hearing loss.

Acoustic neuroma: more accurately vestibular schwannoma; usually causes progressive unilateral sensorineural hearing loss and tinnitus.

Head trauma: may damage the cochlea, CN VIII, temporal bone, or central auditory pathways.

Meningitis: important acquired cause of sensorineural deafness, particularly after bacterial meningitis.

Congenital: genetic disorders, congenital infections, structural abnormalities, and perinatal causes.

Key Clinical Pattern

Remember the first division as:

Conductive deafness → external or middle-ear problem.

Sensorineural deafness → cochlea or auditory nerve problem.

The common conductive causes are:

Ear wax + middle-ear disease.

The major sensorineural causes to remember are:

Noise exposure + ototoxic drugs + Ménière disease + vestibular schwannoma + meningitis + congenital causes.

A particularly useful correction is:

Otosclerosis classically causes conductive hearing loss because of stapes fixation, although advanced cochlear involvement can produce a sensorineural component.