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