Disorders of the Ear Flashcards
Example of conductive hearing loss
otosclerosis
Otosclerosis: disease process
- osteodystrophy of endochondral bone leading to bone remodeling
- effects otic capsule bone (temporal bone), where stapes footplate articulates w/ the vestibule
- slowly progressive so hearing loss occurs gradually
Otosclerosis: inheritance
- autosomal dominant, 40% penetrance
- can also affect inner ear function
Otosclerosis: treatment
- hearing aids
- surgical replacement (stapedectomy, most common): >90% improve, 1% with severe hearing loss
- observation
Sensorineural hearing loss: disease process
- occurs when there is damage to inner ear
Sensorineural hearing loss: 3 categories
- sensory: damage to hair cells
- neural: damage or loss of auditory neurons
- strial: damage or degeneration of stria vascularis
- *most patients have components of each**
Sensorineural hearing loss: examples
- DFNB1
- noise induced hearing loss
- auditory neuropathy
DFNB1: disease process
- autosomal recessive SNHL due to mutation in GJB2 that encodes connexin 26
- accounts for 50% of congenital, autosomal recessive nonsyndromic hearing loss
DFNB1 treatment
- cochlear implantation effective in most patients
Noise induced hearing loss: prevelance
- most common cause of preventable SNHL
- common diagnosis for workman’s compensation
Noise induced hearing loss: cause
- most frequently occurs from exposure through years >90dB
- can result from single exposure to very loud noise
Noise induced hearing loss: disease process
- initial damage occurs at post-synaptic structures and afferent fibers innervating inner hair cells
- later there is loss of hair cells and auditory neurons and fibers
Auditory neuropathy: clinical presentation
- absent ABR with intact otoacoustic emissions
Auditory neuropathy: cause and treatment
- DFNB9: mutation in otoferlin
- treatment: excellent results with cochlear implantation
Auditory neuropathy: otoferlin (DFNB9)
- otoferlin is a calcium sensitive protein involved in synaptic vesicle release from hair cells
- otoferlin mutation hair cells are present and function except fail to release glutamate to activate auditory nerve
Hearing assessment: subjective vs. objective
- subjective: audiogram
- objective: auditory brainstem response(ABR), otoacoustic emissions(OAE)
Auditory brainstem response
- test integrity of auditory system through the brainstem
- NOT used as a screening test
- used when newborn fails OAE
Otoacoustic emissions
- low intensity sounds recorded from ear canal response to stimuli
- reflect OUTER HAIR CELL function
- most common test for newborn hearing
How can you still pass OAE and be deaf
- auditory nerve dysfunction
Chochlear implants
- electrodes placed in chochlea that directly stimulate the auditory nerve, bypassing the non functioning hair cells
- patients usually get about 8 channels
Hybrid hearing process
- shorter and thinner chochlear electrodes preserve residual low frequency hearing
- patients use both acoustic and electrical stimulation
Vestibular ocular reflex
- allows for gaze stabilization during head motion
- hair cells of utricle, saccule and semicircular canals are activated or inhibited and lead to movement of eyes in opposite plane/direction so images remain stable on the retina
Nystagmus
- acute abnormal activation or inhibition of vestibular nerve that drive eye movements in absence of head motion
Vertigo
- illusion that the external environment is in motion
- due to nystagmus
Videonystagmogram (VNG) & Electronystagmogram (ENG)
- use caloric stimulation to create currents in endolymph that drive VOR
Caloric stimulation
- irrigation of external auditory canal with cold or warm water/air
ENG/VNG caloric testing
- Cold water: inhibitory current like a head turn to opposite side; slow phase towards irrigated ear and fast (nystagmus) towards opposite ear
- Warm water: excitatory current like a head turn to same side; slow phase away from irrigated ear and fast (nystagmus) towards irrigated ear
Meniere’s disease signs
- fluctuating, low frequency SNHL
- recurrent vertigo
- tinnitus in affected ear
- aural fullness or pressure
Does meniere’s disease effect one ear or both
- only ONE ear
Cause of meniere’s disease
- unknown
- affected ear always has endolymphatic hydrops (swelling of endolymphatic fluid compartment)
- not everyone with endolymphatic hydrops has meniere’s disease*
Treatment of meniere’s disease
- low salt diet and diuretic: common and effective treatment
- steroids
- surgery for intractable cases (
Surgical management of intractable meniere’s disease
- endolymphatic shunt (most common)
- labyrinthectomy
- vestibular nerve section
Endolymphatic shunt
- silastic shunt into endolymphatic sac
- controversial: 70% success rate
- non destructive outpatient with short recovery
Labyrinthectomy
- destruction of vestibular organs, requires compensation period (3-6weeks)
- surgical: 95% success rate, total hearing loss-best for those with poor hearing
- chemical (gentamicin): 70% success rate, 20% hearing loss, long term compensation sometimes not complete
Gentamicin
- affects vestibular cells first and then chochlear cells
- must assess vestibular function not hearing because by the time it effects hearing there will already be perminent hearing loss
Vestibular nerve section
- most complex procedure, required craniotomy
- 90-95% success rate, 5% hearing loss
- best for young patients with good hearing
- 3-6 weeks recovery period
Conductive hearing loss
- problem with ear canal, tympanic membrane and or ossicles
- does not effect ability to discriminate sounds or understand words
