People with mild Alzheimer’s disease make more mistakes on a driving test than older people with no cognitive problems, according to a study published in the September 14 issue of Neurology.

The study involved an on-road driving test with 32 people with mild Alzheimer’s disease and 136 people with no disorders affecting cognition. The people with Alzheimer’s disease were still driving, although some had reduced their driving due to restrictions imposed by themselves or their families.

The 45-minute test included “on-task” time when the drivers were given verbal instructions to follow a route, as well as time when the drivers were not “on task,” or were not asked to remember and follow instructions.

The people with Alzheimer’s were more likely to make driving errors during the route-following task than those without Alzheimer’s. For example, more than 70 percent of the people with Alzheimer’s made at least one wrong turn while following the route, while about 20 percent of those without Alzheimer’s made at least one wrong turn. And nearly 70 percent of those with Alzheimer’s made two or more safety errors, such as erratic steering or going onto the shoulder, while following the route, compared with about 20 percent of those without Alzheimer’s.
Performing the task accentuated the safety gap between the two groups compared with periods when drivers were not asked to follow specific instructions.

“There was no difference in the basic control of the vehicle for the people with Alzheimer’s,” said study author Matthew Rizzo, MD. “This leads us to believe that the mental demands of following verbal instructions and navigating a new route can compete with drivers’ cognitive resources and potentially impair their driving abilities.”

People with Alzheimer’s who were familiar with the area of town where the test was conducted did not get lost during the test, although those with Alzheimer’s who were unfamiliar with the area were likely to get lost during the test.

“Drivers with early Alzheimer’s may have trouble learning new routes but continue to navigate accurately on familiar routes,” Rizzo said. “This suggests that drivers’ license policies could be considered that would allow driving only in familiar neighborhoods for people with mild dementia.”

Rizzo also noted that some of the people with Alzheimer’s did not make any errors or get lost, and drove safely. “This suggests that some people with mild Alzheimer’s remain fit drivers and should be allowed to continue to drive,” he said.
The study concluded that the driving ability of people with mild cognitive impairment should be assessed with driving tests that include tasks that check their memory and attention skills.

Neurologist David Drachman, MD, who wrote a commentary about the study, agreed that on-road evaluation is the best way to test driving competence. He said, “If the driver with mild Alzheimer’s is safe today, I recommend that a family member ride with him or her at least once a month, and if the observer feels endangered, the driver should no longer operate a vehicle.”