Sensorineural hearing loss is due to damage to the pathway that sound impulses take from the hair cells of the inner ear to the auditory nerve and the brain. Possible causes of SNHL are:
- Age-related hearing loss (presbycusis). This is the natural decline in hearing that many people experience as they get older. It's partly due to damage to the hair cells in the cochlea (hearing organ in the inner ear).
- Acoustic trauma (injury caused by loud noise) can damage hair cells.
- Certain viral or bacterial infections such as mumps or meningitis can lead to loss of hair cells or other damage to the auditory nerve.
- Menière's disease, which causes dizziness, tinnitus, and hearing loss.
Certain drugs, such as powerful antibiotics, can cause permanent hearing loss. At high doses, aspirin is thought to cause temporary tinnitus - a persistent ringing in the ears. The antimalarial drug quinine can also cause tinnitus, but it's not thought to cause permanent damage.
Acoustic neuroma. This is a benign (non-cancerous) tumour affecting the auditory nerve. It needs to be observed by an ENT consultant and is sometimes treated.
Other neurological (affecting the brain or nervous system) conditions such as multiple sclerosis, stroke, or a brain tumour.
A conductive hearing loss is one that affects the structures that conduct the sound to the inner ear - this includes both the middle and outer ear. Common causes of conductive hearing loss are, wax build up, fluid or infection in the middle ear, perforated eardrum or damage to the middle ear bones.
Many cases of conductive hearing loss can be treated by ENT consultants. Wax and fluid build-up is easily treated, an infection can be treated with antibiotics, a ruptured eardrum can be patched and damaged middle ear bones can be replaced in surgical procedures.
The term mixed hearing loss is used to describe a hearing loss that is a combination of conductive and sensori-neural loss - in other words affecting both the outer/middle and inner ear.
Sensory hearing loss originates in the inner ear and neural hearing loss originates from structures or systems beyond the inner ear (eg. the auditory nerve or the central nervous system).
With regard to the configuration of the hearing loss, the audiologist is looking at qualitative attributes such as:
- Bilateral (both ears) versus unilateral (one ear) hearing loss
- Symmetrical (same level/severity of hearing loss in both ears) versus asymmetrical hearing loss (different levels/severity of hearing loss in each ear)
- High-frequency/pitched versus low frequency/pitched hearing loss
- Progressive versus sudden hearing loss
- Stable versus fluctuating hearing loss.