Presbycusis: A human temporal bone study of individuals with downward sloping audiometric patterns of hearing loss and review of the literature

Objective. The purpose of this retrospective case review was to identify patterns of cochlear element degeneration in individuals with presbycusis exhibiting downward sloping audiometric patterns of hearing loss and to correlate these findings with those reported in the literature to clarify conflicting concepts regarding the association between hearing loss and morphologic abnormalities. Methods. Archival human temporal bones from individuals with presbycusis were selected on the basis of strict audiometric criteria for downward-sloping audiometric thresholds. Twenty-one temporal bones that met these criteria were identified and compared with 10 temporal bones from individuals with normal hearing. The stria vascularis volumes, spiral ganglion cell populations, inner hair cells, and outer hair cells were quantitatively evaluated. The relationship between the severity of hearing loss and the degeneration of cochlear elements was analyzed using univariate linear regression models. Results. Outer hair cell loss and ganglion cell loss was observed in all individuals with presbycusis. Inner hair cell loss was observed in 18 of the 21 individuals with presbycusis and stria vascularis loss was observed in 10 of the 21 individuals with presbycusis. The extent of degeneration of all four of the cochlear elements evaluated was highly associated with the severity of hearing loss based on audiometric thresholds at 8,000 Hz and the pure-tone average at 500, 1,000, and 2,000 Hz. The extent of ganglion cell degeneration was associated with the slope of the audiogram. Conclusions. Individuals with downward-sloping audiometric patterns of presbycusis exhibit degeneration of the stria vascularis, spiral ganglion cells, inner hair cells, and outer hair cells that is associated with the severity of hearing loss. This association has not been previously reported in studies that did not use quantitative methodologies for evaluating the cochlear elements and strict audiometric criteria for selecting cases.