VANCOUVER—Patients with Alzheimer’s disease exhibit neurocognitive deficits that diminish their safety on the road, despite scoring as well as or better than unimpaired drivers on written tests of driving knowledge, researchers reported at the 2012 Alzheimer’s Association International Conference.

“The important question becomes, at what degree do we compromise safety for the preservation of autonomy?” said Rex Cannon, PhD, Director of the Cognitive Neuroscience Laboratory at Cole Neuroscience Center, Memory Disorder Clinic in Knoxville, Tennessee.

Neurocognitive Evaluations for Safety
Dr. Cannon and his colleagues conducted a study to determine which neurocognitive evaluations best predict unsafe driving in patients with Alzheimer’s disease. Forty-four persons completed a battery of neurocognitive assessments that included the Mini-Mental State Examination, the Delis-Kaplan Executive Function System (D-KEFS), and the Computer Self Test.

The 44 participants were categorized into three subgroups based on age and Alzheimer’s disease status. One subgroup had 30 participants ages 18 to 27, and a second subgroup included seven persons ages 55 to 90 who were experiencing normal aging. A third subgroup comprised seven patients ages 55 to 90 with early Alzheimer’s disease.

All participants used a driving simulator to navigate through two driving tasks, each of which had four turns that participants needed to remember. The researchers monitored 10 driving parameters during the driving simulation.

According to Dr. Cannon, 100% of patients with Alzheimer’s disease were unable to remember the four turns necessary for completing the first route of the driving simulation. Those with Alzheimer’s disease were observed searching and driving aimlessly without asking for help, and they had significantly more errors on the D-KEFS than did the younger drivers. Collision results showed that 42% of patients with Alzheimer’s disease had a collision, compared with 14% of normal elderly drivers and 30% of young drivers.

However, on written tests of driving knowledge, drivers with Alzheimer’s disease scored as well as or better than drivers in the other subgroups. Dr. Cannon attributed this discrepancy to older drivers’ extensive experience and tendency to pay more attention to the questions and answers.

Although persons with Alzheimer’s disease may retain knowledge of driving as well as the physical ability to operate the vehicle, cognitive decline is still likely to decrease their safety on the road. Dr. Cannon and his coauthors have developed a “Turning Over the Keys” equation to better predict when a patient’s neurocognitive performance suggests that driving is no longer safe. The equation incorporates measures of working memory, visual-spatial skills, verbal fluency, executive functions, inhibition and disinhibition, and the Trails 1/4 test. Analysis of the equation is ongoing, said Dr. Cannon.

Self-Regulatory Driving Behavior
Other researchers have approached driver safety from a self-regulatory standpoint. In an ongoing, cross-sectional study, Anna Devlin, doctoral candidate, and Jane McGillivray, PhD, Associate Professor, both of Deakin University in Melbourne, Australia, examined self-regulatory driving behaviors in a sample of 16 older drivers with and without cognitive decline. The researchers sought to determine whether older drivers with cognitive impairment have enough insight into their behavior to effectively self-modify.

All participants completed the Telephone Interview for Cognitive Status–modified version, the Geriatric Depression Scale–Short Form, and the Driving Habits Questionnaire. In addition, the investigators evaluated each participant’s driving ability by surveying a friend or relative who was familiar with the participant’s driving. Discrepancies were noted between passengers’ and participants’ perception of the participants’ driving ability.

Drivers with no cognitive impairment, with probable cognitive impairment, and with cognitive impairment were asked how often they avoid eight potentially dangerous driving situations, and the researchers found that approximately 50% of drivers in all groups and 40% of drivers with probable cognitive impairment always avoided driving at peak hour. Those drivers also reported driving less than 100 km in an average week.

Although none of the drivers with cognitive impairment avoided driving in the rain, 33% of drivers with no cognitive impairment reported always or sometimes avoiding driving in the rain, noted the study authors.

Furthermore, drivers with mild cognitive impairment did not change their driving behavior in the past 10 years, while 50% of drivers with cognitive impairment reported driving slightly less and 50% reported driving much less than 10 years before.

The researchers cautioned that their results are preliminary. “Once sufficient numbers are recruited, we will analyze the relationship between insight into driver difficulty, driver avoidance, and level of cognitive impairment,” they said, noting that if drivers could modify their own behavior, they might increase their safety.

Many patients will also limit their driving if they are encouraged to do so by their physician, according to Dr. Cannon. “At some point, we do have to draw a line. I just don’t know what the line is,” he told Neurology Reviews. “We’re trying to figure out which cognitive test scores would make the best model for finding a statistically significant result that you should not drive because it would not be safe.”

—Lauren LeBano

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