The Aging Inner Ear Flashcards
Cause of presbycusis
Results from aggregate deterioration of the entire auditory pathway
Exact cause speculative: genetic (GRM7 allele) and lifelong acoustic trauma are most imp; other (diet, nutrition, metabolism arteriosclerosis/HLD, ototoxic exposure)
Characteristics of presbycusis
Slowly progressive
Predominantly high-frequency
Diminished speech discrimination (reduced clarity of hearing)
Absence of retrocochlear pathology
Central pathology: increased synaptic time in auditory pathway, increased info processing time, and decreased neural cell population in auditory cortex
Not inevitable
Higher incidence in men
Loss of outer hair cells > inner hair cells
Loss in spiral ganglion cells, CN8 nerve fibers, and neurons in cochlear nuclei
Age-related balance disturbance
Statoconia progressively demineralize and fragment -> decreased responsiveness to gravity and linear acceleration
Positional balance disturbance 2/2 migration of degenerated otoconial debris into dependent PSCC
Decrease in hair cells of maculae of otolith organs and in cristae of SCCs
Type I hair cells affected more
In sensory epithelium: accumulation of inclusion bodies, lipofuscin, & vacuoles
Reduction in # of ganglion cells in Scarpa’s
Lipofuscin accumulation in vestibular nuclei
Loss of purkinje cells in CBL
Presbyastasis
Dysequilibrium with aging
D.O.E.
Types of Presbycusis
- Sensory
- Neural
- Strial (metabolic)
- Cochlear conductive
May occur in isolation or in combination
Sensory presbycusis
B/l, symmetric high-tone hearing loss with an ABRUPTLY sloping threshold
Speech discrimination is related to the frequencies lost
Histo: loss of both hair cells & supporting sustentacular cells isolated to basal turn
Initial flattening of the organ of Corti is followed by secondary neural degeneration
Middle and apical turns containing the speech freq. are usu spared
The pathologic changes are similar to those seen w/ noise trauma
Neural presbycusis
Loss of cochlear neurons involving entire cochlea (i.e. all frequencies)
Significant loss of speech discrimination
No hearing difficulty until the neuronal population falls below a critical number
Downward sloping audiogram w/ variable slope
Strial presbycusis (metabolic)
Flat pure-tone audiogram
Excellent speech discrimination
Slowly progressive hearing loss
Patchy atrophy of stria vascularis in middle and apical turn w/out loss of cochlear neurons
May involve entire cochlea
Quality of endolymph affected by SV degeneration -> loss of energy available to the end organ
Conductive presbycusis
Changes in the mechanical characteristics of the basilar membrane
GRADUALLY sloping high-freq hearing loss
Speech discrim is diminished in relation to the magnitude of pure-tone loss
Noise-induced hearing loss
Prolonged exposure to sound > 85 dB
High-frequency hearing loss maximal at 4000 Hz
Audiogram: b/l notch at 4000 Hz
Vertigo
Cardinal Sx of vestibular dz
Usu rotatory sensation
May take the form of any illusion of mvmt such as rocking, ground rolling, or a sense of falling forward or backward
Usu episodic
Dysequilibrium
Sense of poor coordination w/ erect posture or during a purposeful movment
Usu continuous
Imbalance
Implies an orthopedic (e.g. hip dz) or neurologic (e.g. hemiparesis) problem
Electronystagmography
Graduated series of evaluations of the vestibular and vestibuloocular systems including calorics
Useful for establishing the degree of vestibular fnc, determining side of pathology, and differentiating central from peripheral dz
Posturography
Assesses ability of subject to maintain balance with changing visual and somatosensory input
