Study identifies predictors of Alzheimer's disease longevity
It's among the first questions asked after someone is diagnosed with Alzheimer's disease: “What can we expect?” It's a tough question that has been difficult to answer. But a new study suggests that assessing several key clinical aspects of the disease soon after diagnosis could help families and physicians better predict long-term survival in individuals with AD. These insights also could help public health officials refine cost projections and plan services for the growing number of older Americans at risk for the disease.
The study, funded by the National Institute on Aging (NIA) of the National Institutes of Health (NIH), appears in the April 6, 2004 issue of the journal Annals of Internal Medicine.
The researchers from Seattle's Group Health Cooperative and the University of Washington found that in the years following diagnosis, people with AD survived about half as long as those of similar age in the U.S population. Women tended to live longer than men, surviving about 6 years compared to men who lived for about 4 years after diagnosis. But this gender gap narrowed with age. Age at diagnosis was also a factor. Those who were diagnosed with AD in their 70s had longer survival times than those diagnosed at age 85 or older.
“This finding moves us toward a more precise vision of the course that Alzheimer's may take in people with certain clinical characteristics,” says Eric B. Larson, M.D., M.P.H., director of Group Health Cooperative's Center for Health Studies in Seattle and former medical director at the University of Washington Medical Center. “For doctors, this provides very useful data for gauging the prognosis of an AD patient. For patients and their caregivers, as difficult as this may be to hear, it can help in making appropriate plans for the future.”
During the study, Dr. Larson and his colleagues followed 521 community-dwelling men and women aged 60 and older who had been recently diagnosed with Alzheimer's disease. They were recruited from a database of 23,000 people listed in an Alzheimer's Disease Patient Registry in the Seattle area. The average follow-up period was about 5 years, with an approximate range from 2 1/2 months to 14 years.
As they entered the study, each person was evaluated for cognitive and memory problems and examined for other conditions including heart disease, heart failure, diabetes, stroke, depression, and urinary incontinence. They were also assessed for a history of agitation, wandering, paranoia, falls and walking difficulties. Survival was measured from the time of initial diagnosis until death or when the study ended in 2001.
When compared to the life expectancy of the general U.S. population, overall survival was lower for people with AD in all age groups. For instance, median* survival was 8 years for women aged 70 diagnosed with AD, which is about half the life expectancy of similarly aged American women who do not have the disease. Similar trends were found among 70-year old men with AD who had a median survival time of 4.4 years compared with 9.3 years for the U.S. population.
Survival was poorest among those aged 85 and older who wandered, had walking problems and had histories of diabetes and congestive heart failure. However, the difference in the life expectancy between those who were diagnosed with AD and the general population progressively diminished with age. At 85, for example, median life expectancy for women with AD was 3.9 years after diagnosis compared to about 6 years for women who didn't have the disease. Similarly, 85-year-old men with newly diagnosed AD had a median life expectancy of 3.3 years compared to 4.7 for men of the same age who didn't have AD.
Poor scores on the initial tests of memory and cognitive performance predicted shorter survival time after diagnosis. In fact, a five-point drop in one key test, the Mini-Mental State Exam, during the first year following diagnosis predicted up to a 66 percent increase in the risk of death after that initial year. Walking problems, congestive heart failure, and a history of falls, diabetes and ischemic heart disease were other important predictors of reduced life expectancy after AD diagnosis.
“This study suggests that several critical factors can be evaluated to help answer some of the important questions posed by Alzheimer's disease patients and their families,” says Neil Buckholtz, Ph.D., chief of the NIA's Dementias of Aging Branch. “These conversations are never easy. But these findings could help clarify what patients and families can expect. And ultimately, families who have more precise information on the likely course of the disease should be better prepared to deal with it as it progresses.”
AD is an irreversible disorder of the brain, robbing those who have it of memory, and eventually, overall mental and physical function, leading to death. It is the most common cause of dementia among people over age 65. Recent studies estimate that up to 4.5 million people currently have the disease, and the prevalence (the number of people with the disease at any one time) doubles every 5 years after the age of 65. By 2050, if current population trends continue and no preventive treatments become available, some 13.5 million Americans will have Alzheimer's disease.
The annual national direct and indirect costs of caring for AD patients are estimated to be as much as $100 billion. This suggests that the economic burden will grow as the population ages and the number of AD patients increases.
* Median is the middle value in the set of numbers. In this case, it means an equal number of AD patients lived for longer and shorter times than the median survival cited in this study.
For more information on AD research, as well as on biological, epidemiological, clinical, and social and behavioral research on AD, several publications are available from the NIA including: 2001-2002 Alzheimer's Disease Progress Report and Alzheimer's Disease: Unraveling the Mystery, which includes a CD-Rom animation of what happens to the brain in AD. These publications may be viewed at NIA's AD-dedicated website www.nia.nih.gov/alzheimers, the Institute's Alzheimer's Disease Education and Referral (ADEAR) Center, or by calling ADEAR at 1-800-438-4380.