There are two main categories of hearing loss: conductive hearing loss and sensorineural hearing loss.
Conductive hearing loss relates to a problem with sound travelling from the environment to the inner ear. The sensory system may be working correctly, but the sound is not reaching it. Putting earplugs in your ears causes conductive hearing loss.
Sensorineural hearing loss is caused by a problem with the sensory system or vestibulocochlear nerve in the inner ear.
Basic Ear Anatomy
There are three sections of the ear are:
- Outer ear
- Middle ear
- Inner ear
The basic structures, from outside in, are:
- The pinna is the external portion of the ear
- The external auditory canal is the tube into the ear
- The tympanic membrane is the eardrum
- The Eustachian tube connects the middle ear with the throat to equalise pressure
- The malleus, incus and stapes are the small bones in the middle ear that connect the tympanic membrane to the structures of the inner ear
- The semicircular canals are responsible for sensing head movement (the vestibular system)
- The cochlea is responsible for converting the sound vibration into a nervous signal
- The vestibulocochlear nerve transmits nerve signals from the semicircular canals and cochlea to the brain
Presentation
Hearing loss may be gradual and insidious. Patients may present because others have noticed they are not paying attention or missing details of conversations. Sometimes patients can present with concerns about dementia, when in fact, the issue is hearing loss.
Sudden onset hearing loss (over less than 72 hours) requires a thorough assessment to establish the cause.
There may be associated symptoms alongside hearing loss, which can give clues about the potential cause:
- Tinnitus (ringing in the ears)
- Vertigo (the sensation that the room is spinning)
- Pain (may indicate infection)
- Discharge (may indicate an outer or middle ear infection)
- Neurological symptoms
It is worth noting patients with hearing loss are more likely to develop dementia, and treating the hearing loss (e.g., a hearing aid) may reduce the risk.
Weber’s and Rinne’s Tests
Weber’s test and Rinne’s test are used to differentiate between sensorineural and conductive hearing loss. A tuning fork is used to perform both tests.
Weber’s Test
To perform Weber’s test:
- Strike the tuning fork to make it vibrate and hum (use the palm of your hand or your knee – not the patient!)
- Place it in the centre of the patient’s forehead
- Ask the patient if they can hear the sound and which ear it is loudest in
A normal result is when the patient hears the sound equally in both ears.
In sensorineural hearing loss, the sound will be louder in the normal ear (quieter in the affected ear). The normal ear is better at sensing the sound.
In conductive hearing loss, the sound will be louder in the affected ear. This is because the affected ear “turns up the volume” and becomes more sensitive, as sound has not been reaching that side as well due to the conduction problem. When the tuning fork’s vibration is transmitted directly to the cochlea, rather than having to be conducted, the increased sensitivity makes it sound louder in the affected ear.
TOM TIP: The way I remember which way round these tests are, is to picture Spiderman shooting a web (Weber’s) right in the middle of someone’s face.
Rinne’s Test
To perform Rinne’s test:
- Strike the tuning fork to make it vibrate and hum
- Place the flat end on the mastoid process (the boney lump behind the ear) – this tests bone conduction
- Ask the patient to tell you when they can no longer hear the humming noise
- When they can no longer hear the noise, remove the tuning fork (still vibrating) and hover it 1cm from the same ear
- Ask the patient if they can hear the sound now – this tests air conduction
- Repeat the process on the other side
A normal result is when the patient can hear the sound again when bone conduction ceases and the tuning fork is moved next to the ear rather than on the mastoid process. It is normal for air conduction to be better (more sensitive) than bone conduction. This is referred to as “Rinne’s positive”.
An abnormal result (Rinne’s negative) is when bone conduction is better than air conduction. The sound is not heard after removing the tuning fork from the mastoid process and holding it near the ear canal. This suggests a conductive cause for the hearing loss. Sound is transmitted through the bones of the skull directly to the cochlea, meaning bone conduction is intact. However, the sound is less able to travel through the air, ear canal, tympanic membrane and middle ear to the cochlea due to a conductive problem.
Causes Of Sensorineural Hearing Loss
The causes of adult-onset sensorineural hearing loss are:
- Sudden sensorineural hearing loss (over less than 72 hours)
- Presbycusis (age-related)
- Noise exposure
- Ménière’s disease
- Labyrinthitis
- Acoustic neuroma
- Neurological conditions (e.g., stroke, multiple sclerosis or brain tumours)
- Infections (e.g., meningitis)
- Medications
There are a large number of medications that can cause sensorineural hearing loss. Some of the more common to remember are:
- Loop diuretics (e.g., furosemide)
- Aminoglycoside antibiotics (e.g., gentamicin)
- Chemotherapy drugs (e.g., cisplatin)
Causes Of Conductive Hearing Loss
The causes of adult-onset conductive hearing loss are:
- Ear wax (or something else blocking the canal)
- Infection (e.g., otitis media or otitis externa)
- Fluid in the middle ear (effusion)
- Eustachian tube dysfunction
- Perforated tympanic membrane
- Otosclerosis
- Cholesteatoma
- Exostoses
- Tumours
Last updated July 2021
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