In this prospective cohort study of community-dwelling older persons, we identified five clinically distinct trajectories of disability in the last year of life, and we found that the distribution of these trajectories was quite varied for several different conditions leading to death. The condition with the least variation was advanced dementia, which was characterized by high levels of disability throughout the last year of life. In contrast, for the five other conditions, from 26.8 to 80.0% of subjects were not disabled or had very low levels of disability until only a few months before death (i.e., they had catastrophic disability). These results indicate that for most decedents the course of disability at the end of life does not follow a predictable pattern based on the condition leading to death.
Despite the importance of functional independence to older persons and their families, little is known about the course of disability at the end of life. We found that most decedents had high levels of disability in the last month of life, yet more than half were not disabled 12 months before death. Among the decedents who were not disabled at the beginning of the study, the subsequent course of disability differed considerably, with about one third remaining free of disability, another third having an accelerated course of disability starting about 10 months before death, and the remainder having a rather abrupt development of disability in the last few months of life. The reasons underlying these different disability trajectories, which were observed commonly for each condition leading to death other than advanced dementia, are uncertain. The relative distribution of the trajectories was not sensitive to changes in the hierarchical order of the conditions leading to death.
The course of disability also differed considerably between the two groups of subjects with disability throughout the last year of life. Specifically, the disability was initially mild in the progressive-disability group and worsened gradually over the course of the year, but it was severe during the entire year in the group with persistently severe disability. Although the characteristics of these two groups differed only modestly, the group with persistently severe disability included a large proportion of subjects with advanced dementia. These results are consistent with those of previous studies, which have shown a high burden of disability at the end of life among older persons with advanced dementia.19
In contrast to decedents with advanced dementia, a sizable minority of participants who died from cancer were not disabled during the last year of life. These results belie the notion that cancer at the end of life invariably leads to disability and functional decline.13,20
We also found that the preceding course of disability varied considerably among the subjects with cancer who were disabled at the time of death; only about 40% of these subjects had a classic terminal phase characterized by an abrupt onset of disability in the last few months of life (i.e., catastrophic disability). This heterogeneity in disability trajectories, which was also observed for the two largest groups of subjects — those with organ failure and those who were frail — suggests that personal care needs at the end of life cannot be easily predicted for most older persons and raises concerns about policies that establish benefits for end-of-life care primarily on the basis of disease-specific criteria.21
Other investigators have postulated and provided supporting evidence that disability at the end of life follows distinct but predictable trajectories for cancer, organ failure, and frailty.13
These findings were based on data collected at annual intervals, and disability scores were averaged across all decedents with a specific condition leading to death. In contrast, we first identified clinically distinct trajectories of disability using data that were collected at monthly intervals, and we subsequently evaluated the distribution of these trajectories according to the condition leading to death. Each of the disability trajectories had considerable face validity, and the predicted values for the severity of disability did not differ from the observed values. In contrast to the approach used in a previous study,13
advanced dementia was evaluated as a distinct condition leading to death, and a widely accepted and validated phenotypic definition of frailty was used.14,22
These enhancements probably explain the smaller proportion of unclassified decedents in the current study than the previous study13
(14.9% vs. 23.6%) and, when coupled with the older average age of subjects and the requirement that decedents also have no reported history of chronic lung disease, they probably account for the relatively small number of sudden deaths in the current study.
Our study has several limitations. First, about one third of the decedents met criteria for more than one condition leading to death. Because older persons often have multiple coexisting conditions,23
the identification of a single condition leading to death may not always be feasible. When overlap was allowed among these conditions, the relative distribution of the disability trajectories did not change appreciably. Second, the use of information from death certificates is an imperfect strategy for classifying conditions leading to death. Previous research has shown that the concordance between coding of death certificates by a nosologist and an adjudicated cause of death is high for cancer and moderate for congestive heart failure and chronic lung disease but only fair for dementia,24
largely because of the underreporting of dementia on death certificates. We used data from cognitive testing in addition to coding by a nosologist to classify advanced dementia as a condition leading to death. Finally, because our study participants were members of a single health plan in a small urban area and were oversampled for slow gait speed, our results may not be generalizable to older persons in other settings. However, the demographic characteristics of our cohort did reflect those of older persons in New Haven County, Connecticut, which are similar to the characteristics of the U.S. population as a whole, with the exception of race or ethnic group.7
Our results suggest that the need for services at the end of life to assist with essential activities of daily living is at least as great for older persons dying from organ failure and frailty as for those dying from a more traditional terminal condition such as cancer, and that the need is much greater for older persons dying from advanced dementia. Nonetheless, the absence of a predictable disability trajectory based on the condition leading to death for most decedents poses challenges for the proper allocation of resources to care for older persons at the end of life.