According to the criteria of the Diagnostic and Statistical Manual of Mental Disorders
edition (DSM-IV) (8
), a diagnosis of dementia requires two main components: 1) loss of memory and at least one other cognitive domain, and 2) decline in social or occupational functioning due to cognitive impairment. In the oldest old, however, it can be extremely difficult to determine the contribution of cognitive loss to the loss of functional abilities. The extreme elderly comprise a population with high rates of sensory losses, medical comorbidities, physical disability, frailty, and fatigue. These factors all contribute to loss of abilities, such as driving, managing financial matters and other functional losses associated with dementia in younger elderly. Here we discuss some of the challenges encountered in The 90+ Study
, a population-based investigation of the oldest old in Laguna Woods, California, and highlight methods that can be applied in the clinic as well as in research studies.
3.1 Sensory Loss
Although most people are aware that the oldest-old suffer from sensory difficulties, many may be surprised about the magnitude of the problem. In The 90+ Study
, the majority of participants (72%) had significant hearing loss, vision loss, or both (9
). One population-based study found that 90% of people aged 80–92 had some level of hearing loss (10
). Similarly, visual losses frequently occur in this age group. Of the different types of vision loss, age-related macular degeneration is one of the most prevalent and debilitating. A meta-analysis of population-based studies showed that macular degeneration increases greatly with age and 16% of white women aged 80 and older have the condition (11
The very high prevalence of visual and hearing loss in the oldest-old make evaluations for cognitive impairment difficult and may lead to a misclassification bias where dementia is diagnosed more frequently in people with sensory losses. However, some studies have suggested that the sensory loss itself may be indicative of neurodegeneration and, thus, related to cognitive decline. For example, a case-control study of 100 AD patients and 100 matched controls found that hearing loss was associated with the severity of cognitive dysfunction in both the demented patients and normal controls after controlling for relevant variables (12
). A prospective cohort study found that vision impairment and combined vision and hearing impairment predicted both cognitive and functional decline in a sample of older women (13
). Although there is some evidence that sensory losses may be related to neurodegenerative processes associated with cognitive decline, in order to properly assess the oldest-old, various methods to compensate for vision and hearing loss should be implemented.
Our experience in The 90+ Study
led to standardized changes in our administration of all tests and the design of forms. Participants with hearing difficulties are provided with amplifiers. To maximize visibility, stimuli are presented in size 90 font for all subjects. Additionally, we have modified several common neuropsychological tests. For example, when administering the Mini-Mental State Examination (14
) and the California Verbal Learning Test-II Short Form (15
), the words for recall are spoken in a loud, clear voice and simultaneously shown to the participant on a card with large typeface. This type of multi-modality presentation promotes the ability of the participant to register the appropriate word despite sensory limitations. These compensations for sensory losses are crucial for valid assessment of the cognitive abilities in the oldest old.
In the oldest-old, high comorbidity rates make it difficult to parse out impairments related to neurodegenerative disorders such as AD from impairments related to medical illness. In a study of participants from The 90+ Study
without functional disability (average age=94), almost all participants had at least one major medical illness or cardiovascular risk factor (cerebrovascular disease, cardiac disease, arthritis, diabetes, thyroid disease, hypertension, or high cholesterol) and 62% had two or more (16
). A population-based study of Danish centenarians reported that the average centenarian (demented or cognitively normal) had more than four chronic conditions or diseases (17
). These studies demonstrate the high levels of comorbidities in oldest old individuals and further complicate the interpretation of their neuropsychological results and losses in daily function.
It has been hypothesized that with the extension of lifespan and advances in medical science, the health of our elderly population may be improving. However, a recent Swedish survey of people aged 77 and older showed that between 1992 and 2002 the prevalence of various medical conditions increased (18
). Although people are living longer, they are not necessarily living healthier. Moreover, higher rates of medical illnesses result in greater medication use and these medications can affect cognitive performance through a number of mechanisms. A large, Finnish study examined medication usage in elderly people (aged 64 years and older) in the early and late 1990s (19
). In less than a decade, the average number of medications taken daily per person increased from 3.1 to 3.8. In people aged 85 and older, 97% took at least one prescription medication, with the average man in this age category taking more than five medications and the average woman, seven. These medical illnesses and medications frequently lead to delirium, which is probably under-recognized, especially in the oldest-old and those with dementia (20
3.3 Lack of Normative Data
Ideally we would like to measure if an individual’s cognitive performance has declined from a previous level. However in practice, it is typically necessary to compare performance to standardized age-specific norms to determine if a person has cognitive loss. Hence, appropriate normative data must be available. Very few normative studies have included large numbers of people aged 90 and older (21
) and several have excluded the oldest-old entirely (23
). For example, a paper written with the purpose of providing normative data over age 80 for the California Verbal Learning Test included only 39 people aged 77–94 (25
). Age-associated cognitive losses accelerate in the ninth and tenth decades of life. A study examining nearly 200 non-demented participants aged 85 and older found that neuropsychological test scores were significantly affected by age, education and gender. The authors concluded that using normative data from younger populations could potentially result in over-diagnosing cognitive impairment in older age groups (26
With data from The 90+ Study
, we recently published normative data for several commonly used neuropsychological tests. In this publication, the norms from 339 non-demented participants (average age=94) are presented with age-specific means, standard deviations, and percentiles (3
). These data are from a well educated, mostly Caucasian sample, reflecting the composition of our population. While only a first step, these normative values may be useful to clinicians and researchers. Future normative studies encompassing more diverse populations of oldest-old are necessary.
Functional disability is very prevalent in the oldest-old. One study of people aged 84–90 found that only 23% had mild disability or were free from disability entirely (27
). The 90+ Study has examined the prevalence and incidence of disability. Difficulty in Activities of Daily Living (28
) (difficulty with or needing help with feeding, dressing, bathing, toileting, transferring, and walking indoors) was present in 71% of 90–94 year olds, 89% of 95–99 year olds, and 97% of centenarians (29
). In people aged 90–94 with no disability, more than 8% became disabled each year; in people aged 95 and older, the incidence of disability increased to 26% per year (16
Functional disability can be due to physical impairment, cognitive impairment, or both. As a dementia diagnosis requires functional loss specifically due to cognitive impairment, it is essential for the researcher or care provider to probe extensively to accurately determine the cause(s) of the disability. Moreover, unlike traditional disability assessments, the information about functional abilities must be obtained from a variety of sources as well as the individual being evaluated. Reports may vary considerably when obtained by self-report, the individual’s family, friends, or care providers. In many cases, clinical judgment must be used in addition to the information gathered, particularly when determining the contribution of cognitive loss to functional disability.
3.5 Fatigue and Frailty
Frailty has been characterized as a syndrome of weakness, fatigue, and decline in physical activity (30
), and is associated with many negative health outcomes (31
). It is very common in the extreme elderly. In the Cardiovascular Health Study, frailty was present in 7% of elderly overall, but in almost a quarter (23%) of participants aged 90 and older (32
). The concept of frailty is highly interrelated with disability and comorbidity (31
). A component of frailty frequently present in the elderly is extreme fatigue, a factor we greatly underestimated before conducting research in this population. Both fatigue and frailty can be due to comorbidities, medication usage, sensory problems, or a variety of other, even unknown, factors. Not surprisingly, fatigue has effects on cognitive performance and functional abilities that are difficult to separate from cognitive impairment due to a neurodegenerative disorder.
The most obvious initial step for accommodating frailty and fatigue is to shorten neuropsychological and other tests given to the oldest-old. For neuropsychological testing in The 90+ Study
, we shortened versions of several common tests and omitted some tests that were considered to be too tiring for the participants. The battery can be completed in approximately forty-five minutes (for a detailed explanation of the battery, see (3
)). However, even though the utmost care has been taken to design the battery to be as short as possible while still collecting the needed data, approximately 20% of people still omit at least one test because of fatigue (3
). Another strategy for acquiring the necessary data from participants who are frail or fatigued is to complete the testing in multiple short visits. This strategy can cause difficulties, however, as the individual’s cognition and health can change between visits, or they may be unable to schedule additional assessments. In the end, flexibility is crucial and the limitations of each participant or patient must be taken into consideration.
3.6 Cultural and Environmental Expectations
Key to the diagnosis of the clinical syndrome of dementia is report from family, friends or co-workers who document a loss of cognitive or functional abilities. An informant is so crucial for obtaining information that most dementia research includes a designated informant for additional data gathering. “He’s good for his age” is a red flag when obtaining information about an oldest old individual. Social and cultural expectations contribute to age adjustments in our expectations and evaluations of abilities. Individuals 90 or 100 years old who are reported by family “to have a memory that is as sharp as a tack” may remember things well from long ago but not be able to recall the morning breakfast conversation or names of grandchildren. Repetitiveness and other signs of forgetfulness may be regarded as endearing. Finally, expectations for occupational and social functioning are typically modest, and may be further attenuated by medical illnesses, pain, sensory losses, or loss of mobility. In The 90+ Study structured phone interviews were conducted with informants multiple times during the length of the study. During these interviews, trained interviewers probed extensively regarding the participants’ cognitive and functional abilities to try to elucidate whether diminished expectations are in fact due to cognitive losses.