Aging, arthritis, and disability

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The prevalence of arthritis increases markedly with age, with osteoarthritis being the most common form of arthritis in older persons. Because arthritis is so ubiquitous in the elderly and is rarely associated with mortality, it is often viewed as a benign condition of aging. In this issue of Arthritis Care & Research, however, Song and colleagues (1) present evidence to suggest that arthritis is hardly benign. In their study, nearly one-quarter of the new cases of activities of daily living (ADL) disability were attributable to arthritis.

Placing this study into context requires an appreciation of the importance of ADL disability as an outcome in older persons. ADL refer to the core set of basic activities that individuals need to perform to live independently. Generally, these activities include the ability to bathe, dress, transfer from a bed to a chair, use a toilet, and eat. Elderly who require the assistance of another person to complete these activities are considered to be disabled in ADL function. Generally, before elderly individuals become disabled in ADL function, they will report difficulty with these tasks, as well as higher order tasks such as doing housework or using transportation (2).

Clinicians often fail to recognize ADL impairments in their patients (3). This perhaps reflects the biomedical focus of training with its overemphasis on disease lists and underemphasis on global measures of well-being such as functional status. Among geriatricians and gerontologists, however, there is almost an obsession with ADL function, with much of the day-to-day practice of the discipline focused on the prevention of, rehabilitation from, or management of ADL disability (4).

The need to focus on ADL function as a fundamental outcome in older persons is well justified. Persons who are disabled in ADL function can not successfully live alone. They will either be dependent on the assistance of a caregiver, or will need to live in an assisted-living or nursing home environment. ADL dependence is by far the leading indication for nursing home placement. However, it is important to remember that most individuals with ADL dependence are cared for by family caregivers, often at large personal and financial sacrifice (5). Patients who report that they are dependent in ADL function are also at risk for many other adverse health outcomes (6, 7). Functional measures such as ADL function are among the strongest predictors of mortality in the elderly. These measures are generally better predictors of mortality than the elderly person's disease because they represent the end impact of disease, or the extent to which the diseases really matter.

Given the importance of ADL disability in the elderly, the 24% population-attributable risk described by Song et al has considerable public health implications. At first glance, it may seem surprising that arthritis can be the cause of so much disability in the elderly. When one thinks of reasons why an elderly person becomes ADL disabled to the point of needing nursing home care, stroke and hip fracture are more likely than osteoarthritis to be considered as principal causes. However, the importance of arthritis becomes more apparent when one examines the typical pathways to disability in the elderly.

There are 2 general pathways that lead toward disability: a catastrophic pathway and a chronic, insidious pathway (8, 9). Catastrophic disability refers to disability that develops suddenly, usually in response to a severe precipitating event. Hip fracture and stroke are the most common causes of catastrophic disability in the elderly (8, 10). It is possible for an elderly person with catastrophic disability to progress from totally normal function to severe disability, including the need for assistance in multiple ADL, over the course of several days or hours.

In contrast, chronic, insidious disability develops slowly, and conditions such as osteoarthritis may have a large impact on this process because of their high prevalence. Persons who move along the chronic pathway will often report disability, but will generally be unable to pinpoint when it occurred. However, these persons may report that they progressed over many years from being able to run short distances to having difficulty walking moderate distances to finally having difficulty with basic ADL such as bathing or dressing. Catastrophic disability may be more immediately traumatic to patients than chronic, insidious disability. Clearly, more rehabilitation resources are expended on patients with catastrophic disability than on those with chronic, insidious disability (11). However, the chronic pathway of disability probably accounts for a greater proportion of disabled elderly than the catastrophic pathways (9).

Although arthritis is almost never a cause of catastrophic disability, it probably contributes to many, if not most, cases of insidious disability. However, in an individual patient, one can rarely cite arthritis as the cause of disability. Similar to most syndromes of aging, ADL disability cannot usually be accounted for by any single condition (12). Rather, insidious disability results from the accumulation of risk factors that over time render an elderly person vulnerable to declining function (4, 13). Although Song et al demonstrated that, in a statistical sense, almost 25% of disability is attributable to arthritis, it would not be correct to claim that arthritis is the cause of disability in 1 of 4 individuals with ADL dependence. In contrast, a conclusion stating that arthritis is the contributing cause in 75% of patients with ADL disability, and on average accounts for one-third of the disability is clinically very plausible.

The conclusion that arthritis fully accounts for disability in few elderly persons but contributes to disability in most elderly persons has fundamental implications for the fields of rheumatology and geriatrics. First, it suggests that ADL function should be a fundamental clinical marker in patients with arthritis. Second, arthritis should be considered a potentially treatable cause of disability in most disabled elderly. However, we should not consider arthritis in isolation. Clinicians and researchers need to better examine how arthritis interacts with other conditions to cause disability. Third, preventing arthritis, or minimizing its consequences through effective rehabilitation, is likely to be a useful approach to preventing or minimizing disability in the elderly.

The overall impact of arthritis, particularly osteoarthritis, on old age disability is likely large, perhaps equaling or exceeding the impact of stroke and hip fracture. However, arthritis receives much less notice as a cause of disability than these other conditions, probably because its impact is slow and progressive, and because it generally performs in a supporting rather than a starring role. Efforts to prevent disability in older persons would be enhanced if arthritis were given more “star treatment” by clinicians and funding agencies.

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