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PRESBYCUSIS
Types of Presbycusis

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The Human Ear
What is Presbycusis?
Types of Presbycusis
Prevention

PRESBYCUSIS

PRESBYCUSIS

Types of Presbycusis

 

  • Sensory presbycusis refers to epithelial atrophy with loss of sensory hair cells and supporting cells in the organ of Corti. This process originates in the basal turn of the cochlea and slowly progresses toward the apex. These changes are correlated with a precipitous drop in the high-frequency thresholds, which begins after middle age. The abrupt downward slope of the audiogram begins above the speech frequencies; therefore, speech discrimination often is preserved. Histologically, the atrophy may be limited to only the first few millimeters of the basal end of the cochlea. The process is slowly progressive over time. One theory proposes that these changes are due to the accumulation of lipofuscin pigment granules.

     

  • Neural presbycusis refers to atrophy of nerve cells in the cochlea and central neural pathways. Schuknecht estimated that 2,100 neurons are lost every decade (of 35,000 total). This loss begins early in life and may be genetically predetermined. Effects are not noticeable until old age, because pure-tone average is not affected until 90% of neurons are gone. Atrophy occurs throughout the cochlea, with the basilar region only slightly more predisposed than the remainder of the cochlea. Therefore, no precipitous drop in the high-frequency thresholds on audio is observed. A disproportionately severe decrease in speech discrimination is a clinical correlate of neural presbycusis and may be observed before hearing loss is noted because fewer neurons are required to maintain speech thresholds than speech discrimination.

     

  • Metabolic (ie, strial) presbycusis results from atrophy of the stria vascularis. The stria vascularis normally maintains the chemical and bioelectric balance and metabolic health of the cochlea. Atrophy of the stria vascularis results in hearing loss represented by a flat hearing curve because the entire cochlea is affected. Speech discrimination is preserved. This process tends to occur in people aged 30-60 years. It progresses slowly and may be familial.

     

  • Mechanical (ie, cochlear conductive) presbycusis results from thickening and secondary stiffening of the basilar membrane of the cochlea. The thickening is more severe in the basal turn of the cochlea where the basilar membrane is narrow. This correlates with a gradually sloping high-frequency sensorineural hearing loss that is slowly progressive. Speech discrimination is average for the given pure-tone average.

* Information on this page was taken from http://www.emedicine.com/ent/topic224.htm