By Kristina Fiore, Staff Writer, MedPage Today
Published: February 11, 2009
Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston.
IOWA CITY, Iowa, Feb. 11 -- The difficult judgment call on whether Alzheimer's patients are safe to drive can be helped by a battery of cognitive tests, researchers here said.
* Explain to interested patients that tests of memory, visual, and motor abilities may predict which patients with Alzheimer's disease may make more safety errors while driving.
Patients who performed better on these tests made fewer errors during a supervised test drive, Jeffrey D. Dawson, M.D., of the University of Iowa, and colleagues reported in the Feb. 10 issue of Neurology.
"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," Dr. Dawson said.
To determine whether performance on tests of cognition, visual perception, and motor function could predict the level of safety in licensed drivers with early Alzheimer's, the researchers conducted a controlled trial of 40 patients with mild disease and 115 patients without dementia.
All participants were tested on a battery of cognitive, visual, and motor tasks, from which the researchers calculated a composite measure of cognitive impairment (COGSTAT).
An experimental drive was conducted aboard ARGOS (Automobile for Research in Ergonomics and Safety), which has hidden instrumentation and sensors. Participants drove a supervised 35-mile test drive on roads within and surrounding Iowa City.
A certified safe driving instructor reviewed video tapes of each drive to assess the number and type of safety errors made by the drivers.
The researchers found that drivers with Alzheimer's disease committed an average of 42 safety errors per drive, compared with an average of 33.2 for controls.
Lane observance errors were significantly more common in the Alzheimer's group, but no other general category of errors was significantly more common in Alzheimer's patients.
"This suggests that patients with mild Alzheimer's have the ability to handle certain aspects of driving," the researchers said.
Some of the more serious errors in this class included straddling the center line and failing to proceed through the intersection even though the light had turned green.
Drivers with higher overall cognitive function as measured by COGSTAT tended to make fewer total safety errors, the researchers said.
Other tests that were significant predictors of safety errors among drivers with the disease included working memory, visual search and visual motor speed, visuo-constructional abilities, and motor function.
"Given that driving puts demands on diverse cognitive functions, it is unlikely that a test of any single cognitive ability will be an accurate predictor of driving safety," the researchers said.
The study may have been limited by a lack of investigation of other environmental factors, such as having family members in the vehicle and time of day, as well as a possible lack of generalizability because only seven of the 40 patients in the experimental group were women.
Still, the researchers concluded that for predicting safety errors within the Alzheimer's disease group, "off-road neuropsychological tests of cognition, vision, and motor abilities gave additional information above and beyond diagnosis alone. Hence, performance on these tests can be helpful when predicting whether a patient with Alzheimer's disease can safely drive a vehicle."