| Abstract #18, Date 2/14/99, Session C, Podium , 2:00p |
| Morphometric analysis of age-related changes in the human basilar membrane |
| *K.A. Bhatt, M.C. Liberman, J.B. Nadol (Massachusetts Eye & Ear Infirmary) |
The histopathologic correlates of age-related hearing loss suggest that there are several categories of presbycusis, including degeneration of sensory, and neural elements, and the stria vascularis. In some cases there is inadequate histopathologic change to explain the observed SNHL, leading to the proposal of an "indeterminate category." Some authors have proposed changes in the basilar membrane (BM) as a possible mechanism of hearing loss in the indeterminate category of presbycusis (Nadol, Oto H N Surg, 1979; Ishii, Eur Arch Otorhin, 1994). The objective of this study has been to quantify changes in the BM with age, and correlate these changes with patterns of hearing loss in patients. Under high-resolution light microscopy (Nomarski optics), BM thickness was measured and the number of tympanomesothelial cells (TMCs) lining the BM was counted in 4 cochlear locations (3, 9, 18, 27 mm from round window) in 92 temporal bones. A "control group" (n=80) included subjects from ten decades of age with normal hearing and/or histopathological findings. An "indeterminate group" (n=12) consisted of elderly patients (ages 64-91) with hearing loss but without obvious significant histopathology. All slides were randomized and numerically coded. Age-related BM thickening was seen in both groups, in both pars pectinata (p < 0.0001) and pars tecta (p < 0.001), but only in the basalmost cochlear region. BM thickness in the indeterminate group was not significantly different from age-matched controls. Counts of TMCs showed age-related decreases in all cochlear regions in both groups. The TMC counts in the indeterminate group were not different from age-matched controls. The lack of morphological differences between control and indeterminate groups suggests that BM histopathology is not a common etiology for age-related hearing loss. Theoretically, age-related BM thickening seen in both groups could change cochlear mechanics and contribute to hearing loss. However, the extreme basal region, to which the thickening was confined, is not tested in routine audiometry. Age-related loss of TMCs does not appear to cause hearing loss, since it was seen in all cochlear regions of the control group. |