The findings will appear in the October issue of the Journal of the American Geriatrics Society.
"As we expected, people with dementia, generally in the mild stages, declined faster than the nondemented individuals," says senior author Janet M. Duchek, Ph.D., associate professor of psychology and of occupational therapy. "But it is very interesting that there also was decline in some of our nondemented participants. This is a preliminary study, but it suggests that testing individuals with mild dementia every six months can be useful to identify those who become unsafe."
Alzheimer's disease is the most common cause of dementia in older adults and affects about 4.5 million Americans. Affected individuals experience memory difficulties and problems with attention and eventually lose the ability to perform complicated tasks like driving.
But according to co-author John C. Morris, M.D., principal investigator of the Alzheimer's Disease Research Center and the Harvey A. and Dorismae Hacker Friedman Distinguished Professor of Neurology, it's impossible to predict driving performance based solely on whether a person has been diagnosed with dementia. That's why the research team, which also included Linda Hunt, Ph.D., formerly at the School of Medicine and now at Flathead Valley Community College in Mont., and David B. Carr, M.D., associate professor of medicine, developed an extensive, 45-minute, in-traffic driving test called the Washington University Road Test.
"Appropriate testing is important," Morris says. "For individuals who still drive safely, it can be reassuring and help them remain independent. It also can be used to follow individuals to detect the development of unsafe driving behaviors and intervene, hopefully before there is an actual crash or other problem."
In a study published by Hunt and the team in 1997, 41 percent of individuals with mild Alzheimer's disease failed the driving test, compared with only 14 percent of those with very mild dementia and 3 percent of nondemented participants.
The current study details longitudinal findings with the same group of participants. The team administered the road test every six months to the individuals who passed the test the first time and then compared the time it took each group to go from "pass" to "fail."
As expected, the mild Alzheimer's group declined the fastest, followed by the very mild dementia group. Surprisingly, performance in the non-dementia group also declined over time, though at a slower rate than the other two groups.
In addition, when data from all three groups was combined, increased age alone appeared to be a risk factor in driving performance.
"While the majority of the nondemented people we tested remained very safe drivers, as we followed them, more and more became unsafe," Morris says. "Age-related changes other than dementia likely contribute to driving performance and should be further investigated in larger groups of older adults."
Duchek and Morris emphasize the need to educate physicians and families about the importance of detecting changes that may impair an individual's driving performance. Signs that should raise concern include an inability to maintain speed or to stay in one lane while driving, hesitating at turns or becoming lost, particularly in familiar areas.
"One of the features of dementia is that individuals lose insight and may not recognize that they are becoming unsafe," Morris explains. "We must increase public awareness about driving issues in demented persons and empower families and health care professionals to intervene before a tragedy occurs."
Duchek JM, Carr DB, Hunt L, Roe CM, Xiong C, Shah K, Morris JC. Longitudinal driving performance in early-stage dementia of the Alzheimer type. Journal of the American Geriatrics Society, vol 51, pp. 1342-1347, October 2003.
Funding from the National Institute on Aging supported this research.
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