Decreasing hair cell counts in aging humans

Deterioration of balance with advancing age is a well-known fact of life. Some investigators have reported a 50% prevalence of dizziness in the elderly. Clinically, progressive dysequilibrium of aging presents as gradually worsening balance due to age-related decline in function of the peripheral vestibular system, central nervous system, vision, and musculoskeletal system. Vestibular function testing has shown clear evidence of age-related changes in peripheral and central sites. Histopathologic changes in the vestibular sensory organs include progressive hair cell degeneration, otoconial degeneration in the otolith organs, and decreasing number of Scarpa's ganglion neurons. Recently, a new quantitative method of assessing vestibular otopathology has been described, utilizing Nomarski differential interference contrast microscopy. This technique has been applied to 67 human temporal bones of individuals from birth to age 100 to create a normative database of total, type I, and type II hair cell counts as a function of age. Results show a highly significant continuous decrease in all counts from birth to age 100, best fit by a linear regression model. Type I hair cell counts in all three semicircular canal cristae decrease at a similar rate, significantly faster than the degeneration observed in type I hair cells of the maculae. Type II hair cell counts decline at the same rate for all 5 sensory epithelia. These normative data provide the basis for comparisons to hair cell counts made in temporal bones from subjects with known vestibular disorders. They also provide a basis for drawing correlations between vestibular function testing and vestibular otopathology.