This chapter reports descriptive data on three neurologic conditions that are often associated with disability in older adults: stroke, Parkinson's disease, and peripheral neuropathy. Data are also included on balance problems and falls, conditions often caused by impairments of neurological control (Horak et al., 1989; Massion, 1992; Tinetti et al., 1988).
Many chronic conditions affecting the neurological system become more prevalent with advancing age (Kurtzke, 1985; Morgante et al., 1992; Schoenberg et al., 1985). Stroke is a leading cause of death in older women and is also a leading cause of disability in activities of daily living (ADLs) and upper extremity tasks in this age group (Eaker et al., 1993; Ettinger et al., 1994). More than 60 percent of elderly women surviving a stroke (Eaker et al., 1993) and over two-thirds of patients affected by Parkinson's disease (Peterson et al., 1988; Sutcliffe et al., 1985; Wade et al., 1986) have significant disability in ADLs. The overall contribution of stroke to disability in the older population is likely to increase in the future, since age-specific incidence rates are stable while case-fatality rates have been progressively declining in the past two decades (Baruch and Wagener, 1992). In spite of this situation, there are few epidemiologic data on the specific characteristics of neurologic diseases associated with functional deterioration.
The study of neurologic conditions in old age is particularly complex, in part because the boundary between normal aging and pathological changes of the brain is difficult to identify. Furthermore, the full impact of neurologic diseases often cannot be easily determined owing to the multifaceted clinical expression of these conditions.
One of the basic approaches of the Women's Health and Aging Study (WHAS) is the development of a priori models of the causal sequences linking diseases (e.g., arthritis), integrated physiologic abilities (e.g., muscular strength of the knee extensor muscles), performance in standard physical tasks (e.g., rising from a chair), and disabilities in daily tasks (e.g., shopping). This framework may help delineate links between specific pathophysiologic mechanisms and disability in selected chronic diseases such as arthritis or respiratory conditions. However, these relationships may be considerably more complex in the presence of pathologic conditions affecting the central nervous system, which may cause problems with a wide range of physical functions, cognition, and other specific cortical functions such as speech, body image, and control of movement. Stroke, for example, may affect any or all ADL and instrumental ADL functions, depending on the location and the size of the lesion.
History of stroke was ascertained by self-report and will be validated by review of medical records and physician questionnaires during a later phase of the study. The data reported here (Table 13.1) are based only on self-report and should be considered with caution, since previous studies have shown that more than one-fifth of self-reported cases are not confirmed when medical records are reviewed (Anderson et al., 1988; Heliovaara et al., 1993). However, even taking into account this possible overestimation, the prevalence of stroke among WHAS participants is substantially higher than in other populations of the same age (Kurtzke, 1985). Since eligibility for the WHAS was based on disability, this differential is consistent with the major role that stroke plays as a cause of disability in older women.
Overall, 15 percent of participants reported a stroke and 73 percent of these participants said they had been hospitalized for a stroke (Table 13.1). The prevalence of stroke, the number of strokes experienced, and the percentage of strokes that resulted in hospitalization were independent of age but strongly associated with disability.
More than 90 percent of the subjects who reported a stroke stated that it occurred more than 6 months before the interview (data not shown). Thus, in the vast majority of these subjects, impairments caused by stroke can be considered stable, at least as far as motor function is concerned (Ernst, 1990; Jongbloed, 1986). Residual symptoms resulting from a stroke are shown in Table 13.2. More than 46 percent of the subjects who reported a previous stroke did not have any residual motor impairment at the time of the interview. This result confirms previous reports on prevalence of impairments in women surviving a stroke (Pinsky et al., 1990). Although the prevalence of motor symptoms did not change substantially with age, it was higher among women receiving help with ADLs than among those with less disability.
The percentage of subjects reporting any residual non-motor symptoms-including impairment in speech, abnormal somatic sensation, dizziness, loss of balance, and vision problems-was higher than the percentage of those who re-
ported residual motor impairment. Overall, the prevalence of non-motor symptoms was inversely related to age. There was no relationship of non-motor symptoms in general with disability, although the prevalence of several specific speech symptoms increased with increasing disability. These data suggest that motor symptoms and changes in speech may be the most important predictors of severity of disability caused by a stroke. The lower prevalence of non-motor symptoms among older subjects is probably the result of selective survival of persons with less severe strokes.
The top of Table 13.3 shows the percentage of individuals reporting a history of Parkinson's disease and current treatment for Parkinson's disease. This approach to ascertainment likely underestimates the prevalence of this condition since a significant proportion of people affected by early-stage Parkinson's disease or parkinsonism will not have been identified. Overall, 2.4 percent of participants reported a history of Parkinson's disease or were being treated, which is similar to the prevalence rates that have been reported in other studies of community-dwelling populations in the same age group (Morgante et al., 1992; Shoenberg et al., 1985). Women in the oldest age group were slightly more likely to have a history of Parkinson's disease or medication use. Evidence of Parkinson's disease was present in 7 percent of women who received help with ADLs, compared with much smaller proportions of women with lesser degrees of disability.
The prevalence of symptoms that typically affect parkinsonian patients was assessed with a standardized questionnaire (Tanner et al., 1990, Table 13.3). The diagnostic value of this questionnaire has been verified in the general population (Tanner et al., 1994). Most of the parkinsonian symptoms assessed by the questionnaire showed a high prevalence in this cohort and a strong relationship with level of disability. However, the specificity of some of these symptoms
for a diagnosis of Parkinson's disease or parkinsonian syndromes is poor in this population, since many items included in the questionnaire ascertain physical problems such as "having trouble rising from a chair" or "poor balance" that may also be caused by more prevalent chronic diseases.
Several studies have documented that the function of the peripheral nervous system, especially sensory function in the distal extremities, declines with increasing age (Falco et al., 1994; Skinner et al., 1984). However, whether aging itself has an independent effect on decline in peripheral nerve function has been questioned (Letz and Gerr, 1994; Paradiso et al., 1989). In the WHAS, the presence of peripheral neuropathy was investigated by asking the participants about abnormalities in somatic sensation and by objectively measuring the threshold for vibratory sensation in the lower extremities (Maser et al., 1989).
The percentage of subjects reporting abnormal somatic sensation decreased with age and increased with level of disability (Table 13.4). A substantially greater prevalence of peripheral neuropathy in those receiving help with ADLs was indicated by the response to the question, "Have you ever burned yourself without feeling pain?" which assesses extremely severe loss of somatic sensation.
Vibratory threshold was measured in the lower extremities using the Vibratron II apparatus (Physitemp Instrument, Inc., Clifton, NJ). This test determines the sensitivity of the large toe in detecting a very small vibratory stimulus as an indicator of large-fiber peripheral nerve function. The method employed a two-alternative forced-choice procedure, in which the woman was required to indicate which of the two periods of "stimulation" applied on the lower surface of the right great toe was accompanied by an actual vibration. The intensity of the stimulus was slowly reduced by approximately 10 percent at each trial until the participant could no longer discern the vibration. When the participant made her first error, the intensity was increased by 10 percent. This process continued, with correct trials resulting in a lowering of intensity and errors resulting in an increasing intensity until a total of five errors were made. The vibration threshold was determined by identifying the five errors and the five lowest correct scores, eliminating the highest and the lowest, and calculating the mean of the remaining eight scores. This scoring method was derived from the protocol developed by Arezzo and colleagues for the Physitemp Instrument, adapted to single-transducer equipment and validated in a series of patients affected by diabetes (Maser et al., 1989). According to this protocol, the test should be considered valid only if 18 or fewer trials are needed and not more than one error is encountered in the first 8 trials.
Only slightly more then 60 percent of the subjects met the above criteria for a valid test, and the percentage not meeting the criteria increased markedly with both age and level of disability. To present a more complete picture of the WHAS population, the measurements obtained from these women are included in the results presented in Table 13.5. Mean vibration threshold increased with age and level of disability, and the entire distribution of scores for vibration threshold was shifted higher with increasing age and level of disability, confirming previous findings (Skinner et al., 1984).
Falls result in physical injury, decline in function, serious morbidity, and institutionalization (Cummings and Nevitt, 1994; Kiel et al., 1991). It has recently been demonstrated that many falls can be prevented by multifactorial intervention programs (Tinetti et al., 1994).
Since many studies have shown that a disturbance in the control of balance is one of the most frequent cause of falls (Tinetti et al., 1988), both conditions are discussed in this section. The control of balance requires the coordinated function of multiple mechanisms and the integrity of the musculoskeletal apparatus (Lord et al., 1994). It is widely recognized that instability in older adults is frequently explained by subclinical deterioration in several subsystems (Horak et al., 1989; Tinetti et al., 1988). The detection of these relatively small impairments requires techniques that cannot be easily implemented in an epidemiologic study. However, even simple performance measures of functioning have been shown to be powerful predictors of falls (Nevitt, 1989).
One-third of WHAS participants reported falling in the past year, and 15 percent fell two or more times (Table 13.6). Among those receiving help with ADLs, nearly half fell in the previous year, and nearly a quarter fell two or more times. Almost half the subjects (45 percent) reported that they had been "anxious or worried or afraid" of falling in the past 12 months, and nearly 20 percent reported limiting their activities some or most of the time because of fear of falling. The percentage of subjects reporting a history of falls, fear of falling, and limitation in activities because of fear of falling was not substantially different in the three age groups, although women age 85 years and older were twice as likely as women age 65 to 74 years to limit their activities most or all of the time because of fear of falling (15 percent versus 7 percent). There was a strong association of fall history and fear of falling with level of disability. One-third of women receiving help with ADLs reported limiting activities some or most of the time because of fear of falling.
Table 13.6 also shows self-report of dizziness, which is quite common in this cohort, and fainting, which occurred in about 5 percent of participants in the past year. The percentage of participants who fainted was very low compared with the percentage who reported falls: this is not unexpected as the main cause of most falls is a dysfunction in the control of balance not associated with loss of consciousness.
Table 13.7 presents data on self-perception of poor balance related to a range of situations in daily life. Again, while an age effect is clearly present, there is a strong association of balance problems with level of disability.
The strong association between balance and disability is further demonstrated in Figure 13.1, which shows performance according to disability level on a series of tests investigating balance, organized in a hierarchical scale (described in detail in Chapter 4). This figure classifies the ability to maintain balance into seven progressively more demanding levels. The percentage of subjects totally unable to perform the entire set of tests, as well as the percentage of subjects unable to perform each level of the tasks, increased with level of disability. Note that in this population self-perception of problems with balance is only modestly associated with age, while performance in balance is highly age-dependent (Table 4.2). This fact suggests the development of lower expectations with aging regarding the ability to maintain stable balance or the development with aging of adaptive behavior that obscures the objective capacity to maintain stable balance.
Conditions that affect the central and peripheral nervous systems are important causes of disability in older persons. Specific diseases (stroke and Parkinson's disease) and conditions (parkinsonian symptoms, peripheral neuropathy, balance problems, and falls) related to the nervous system are common in older disabled women and have a higher prevalence in women with the most severe disability.
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