March 9, 2009
Giving up the car keys is a wrenching decision for anyone with Alzheimer's and their families. Now, a new study shows, doctors may be able to use tests of thinking and perception to help determine whether a person with Alzheimer's disease can safely get behind the wheel. The research was published in the Neurology, the medical journal of the American Academy of Neurology.
"The number of people with dementia is increasing as our population ages, and we will face a growing public health problem of elderly drivers with memory loss," said study author Jeffrey Dawson, Sc.D., with the University of Iowa in Iowa City.
Driving safely is an issue for any driver, particularly older drivers. Per mile driven, the accident rate is nine times higher for those 85 and older compared to younger drivers aged 25 to 69. If someone has failing cognition due to early Alzheimer's or other forms of mental decline, the likelihood of a car crash is much greater.
Most people with Alzheimer's will eventually become unable to drive safely as their disease progresses. Alzheimer's affects not just memory but also thinking, visual perception and motor function, skills that are all critical for safe driving.
However, as more and more people get diagnosed with Alzheimer's at an early and mild stage, it becomes difficult to know when those with the disease should relinquish the car keys. Those with the disease often wish to maintain their independence and continue to drive. Family members may intervene and ban driving prematurely, or encourage continued driving beyond when it is safe, leading to conflicts and dangers to patients and others.
The current study was done to help determine whether objective measures could assess whether it is safe for someone with Alzheimer's to continue to drive.
In the study, 40 drivers with early Alzheimer's disease and 115 of their mentally sharp peers underwent a combination of off-road tests that measured thinking, movement and visual skills. The participants also drove a 35-mile route in a special vehicle in and out of Iowa City. Driving safety errors were recorded by a driving expert, based on a video review of the drive.
The researchers found that drivers with Alzheimer's disease committed an average of 42 safety mistakes. That was 27 percent more than the drivers who did not have Alzheimer's disease, who made an average of 33 safety errors on the test drive.
The most common mistakes in those with Alzheimer's were veering outside of the lane markers and straddling the centerline. Another common mistake in this group was being overly cautious and failing to proceed through an intersection, even though the light had turned green.
For every five years older the participant was, the number of safety errors went up by about two and a half, whether or not a person had Alzheimer's disease. Those with more advanced Alzheimer's tended to commit more driving errors.
"The goal is to prevent crashes while still maximizing patients' rights and freedom to be mobile," Dr. Dawson said. "By measuring driver performance through off-road tests of memory, visual and motor abilities, we may be able to develop a standardized assessment of a person's fitness to drive."
The findings are consistent with earlier studies showing a link between Alzheimer's and poor driving. But just because someone has Alzheimer's disease doesn't mean that they cannot drive. A study last year from Rhode Island, for example, found that many people with early Alzheimer's can, in some cases, continue to drive safely for extended periods.
But regular check-ups are indicated for anyone with Alzheimer's who is still driving. The American Academy of Neurology Guideline on Risk of Driving and Alzheimer's Disease recommends a reassessment every six months for people diagnosed with very mild dementia who continue to drive.
J. D. Dawson, Sc.D., S. W. Anderson, Ph.D., E. Y. Uc, M.D., et al: "Predictors of Driving Safety in Early Alzheimer's Disease." Neurology, Volume 72, pages 521-527, February 2009.