Is there a conductive type of presbycusis?

Many ears that manifest hearing losses caused by aging show combinations of atrophic change in the sensory cells, cochlear neurons, and stria vascularis. When it occurs in pure form, the loss of sensory cells produces an abruptly sloping high-tone threshold loss, the loss of cochlear neurons decreases the capability for speech discrimination, and the loss of strial tissue produces a flat threshold loss. There remains a fourth group of cases that have gradual sloping high-tone threshold losses for which a pathological correlate has not been identified. We performed a quantitative histologic study, using light microscopy on the temporal bones of such cases, and again could find no pathologic explanation. We believe that the findings of this study support the concept of an alteration in cochlear motion mechanics as the most probable cause for the gradually sloping high-tone hearing loss.