sensorineural hearing loss (SNHL)

what is sensorineural hearing loss?

dysfunction of the inner ear or auditory nerve which prevents neuronal transmission to the brain

defects in what structure would cause it to be sensory hearing loss?

cochlea

defects in what structure would cause it to be neural hearing loss?

cochlear nerve

what are the causes of sensorineural hearing loss?

- presbycusis

- ototoxic drugs

- postnatal infections

- noise-induced hearing loss

- cochlear vascular disease

- meniere's

- trauma

- prenatal TORCH

what are the ototoxic drugs?

- streptomycin

- vancomycin

- gentamicin

- chloroquine

- alkaloids

what postnatal infections may cause SNHL?

- measles

- mumps

- meningitis

what is prenatal TORCH?

- TOxoplasmosis

- Rubella

- Cytomegalovirus

- Herpes simplex

what are the more rare causes of SNHL?

- acoustic neuroma

- B12 deficiency

- MS

- brain metastasis

what are the clinical features of SNHL?

- hearing worsens in noisy environments

- volume of own voice may be loud - nerve transmissions impaired

what are the Rinnes test results for SNHL?

- positive

- air conduction > bone conduction

- inner ear/auditory nerve cannot transmit sound information well, regardless of how vibrations reach the cochlea

what are the Weber's test results for SNHL?

- sound is louder in normal ear

- sound to impaired air is not transmitted by damanged inner ear/nerve so only heard in unaffected side

what else can be used to discriminate between CHL and SNHL?

audiogram

what are the results of speech audiometry?

often discrimination loss with increased sound

what are the results of impedance audiometry?

normal acoustic reflex threshold

what would qualify someone for an urgent referral to ENT?

- sudden onset (3 days or less) uni or bilateral hearing loss occurring in the last 30 days which cannot be explained by external or middle ear causes

- unilateral hearing loss associated with focal neurology (sensation loss or facial droop)

- hearing loss associated with head or neck injury

- hearing loss associated with severe infection such as otitis media or ramsay hunt syndrome