Critchley, in 1931 and 1956, drew attention to a number of neurologic abnormalities that he had observed in octogenarians and for which no cause could be discerned other than the effects of aging itself. Several reviews of this subject have appeared subsequently (see especially those of Jenkyn, of Benassi, and of Kokmen [1977] and their associates). The most consistent of the neurologic signs of aging are the following: • Neuro-ophthalmic: progressive smallness of pupils, decreased reactions to light, and near farsightedness (hyperopia) as a result of impairment of accommodation (presbyopia), insufficiency of convergence, restricted range of upward conjugate gaze, frequent loss of the Bell phenomenon, diminished dark adaptation, and increased sensitivity to glare.
• Progressive hearing loss (presbycusis), especially for high tones, and commensurate decline in speech discrimination. Mainly these changes are a result of a diminution in the number of hair cells in the organ of Corti.
• Diminution in the sense of smell and, to a lesser extent, of taste (see Chap. 11).
• Motor signs: reduced speed and amount of motor activity, slowed reaction time, impairment of fine coordination and agility, reduced muscular power (legs more than arms and proximal muscles more than distal ones) and thinness of muscles (sarcopenia), particularly the dorsal interossei, thenar, and anterior tibial muscles. A progressive decrease in the number of anterior horn cells is partially responsible for these changes, as described further on.
• Changes in tendon and frontal reflexes: A depression of tendon reflexes at the ankles in comparison with those at the knees is observed frequently in persons older than 70 years of age, as is a loss of Achilles reflexes in those older than 80 years of age. The snout or palmomental reflexes, which can be detected in mild form in a small proportion of healthy adults, are frequent findings in the elderly (in as many as half of normal subjects older than 60 years of age, according to Olney). Other so-called cortical release signs, such as suck and grasp reflexes, when prominent, are indicative of frontal lobe disease but sometimes are expected simply as a result of aging.
• Impairment or loss of vibratory sense in the toes and ankles. Proprioception, however, is impaired very little or not at all. Thresholds for the perception of cutaneous stimuli increase with age but require the use of refined methods of testing for their detection. These changes correlate with a loss of sensory fibers on sural nerve biopsy, reduced amplitude of sensory nerve action potentials, probably as a result of loss of dorsal root ganglion cells.
• The most obvious neurologic aging changes—those of stance, posture, and gait—are fully described in Chap. 6 and further on in this chapter.
Jenkyn and colleagues, based on their examinations of 2,029 individuals aged 50 to 93 years, have determined the incidence of certain of these common neurologic signs of aging. Notable again is the high frequency of snout and glabellar responses, but also limited downgaze and upgaze in approximately one-third of persons older than age 80 years. Table 28-3 summarizes these data.
With regard to the interesting population of the “oldest old,” those older than 85 or 90 years of age, Kaye and colleagues reported that deficits in balance, olfaction, and visual pursuit are distinctly worse than in younger elderly persons. Also of interest is the observation by van Exel and colleagues that women in this age group perform better than men on cognitive tests.