Oct. 30, 2007
UI study shows that Parkinson's disease impairs normal driving skills
Navigating a new route while driving taxes any driver's memory, attention and cognitive and visual abilities. Patients with mild to moderate Parkinson's disease, however, cope less well with these challenges, making significantly more mistakes and driving less safely than neurologically normal elderly drivers, according to a study by University of Iowa researchers.
Ergun Uc, M.D., associate professor of neurology in the UI Roy J. and Lucille A. Carver College of Medicine, and his colleagues have previously shown that even during normal driving, individuals with Parkinson's disease generally have more safety errors -- lane violations, erratic driving and failure to heed traffic signs -- than drivers without the disease. However, the new study shows that faced with the additional challenges of navigating while driving, Parkinson's disease patients' driving performance was significantly more degraded than that of drivers without the condition.
"The disease appears to limit the Parkinson's disease patients' 'cognitive reserve,' making them even less capable of dealing with additional challenges posed by secondary tasks like navigation," said Uc, who also is a staff physician at UI Hospitals and Clinics and the Veterans Affairs Iowa City Health Care System.
Interestingly, the researchers found that the driving problems patients with Parkinson's disease experienced during navigation were associated more with the patient's level of cognitive and visual impairment than with the severity of the patients' physical symptoms, such as the tremors for which the disease is primarily known. Uc and his colleagues have found the same correlation in other studies that test drivers' ability to handle an additional mental task while driving, such as looking for landmarks or adding numbers.
The findings are part of a larger, longitudinal UI study funded by the National Institute of Neurological Disorders and Stroke examining how Parkinson's disease affects driver safety, with the aim of being able to predict which aspects of the disease contribute most to risky driving. The study is following more than 100 patients with Parkinson's disease for three years, tracking their disease progression as it affects various physical and mental functions and at the same time testing the patients' driving skills and safety as compared to drivers of similar age who do not have any neurological disease.
The new study, which was published in the September issue of Brain, tested the participants' ability to navigate a one-mile route involving several turns based on verbal instructions. The study participants (77 patients with Parkinson's disease and 152 neurologically normal individuals of similar age) received the route instructions before the driving portion of the test started. Once they were able to accurately recite the directions twice in a row, the participants performed the driving test in an instrumented vehicle known as ARGOS (Automobile for Research in Ergonomics and Safety), an ordinary car fitted with monitors, cameras and computers that record the driver's responses.
Drivers with Parkinson's disease were more likely to make incorrect turns, get lost and make safety errors while doing the test compared to control subjects. Patients with Parkinson's disease also took longer to memorize the route details in the first place and needed more time to complete the route than elderly drivers with no neurological disease.
"Our findings suggest that people with Parkinson's disease should be particularly careful when they are driving in unfamiliar environments," Uc said. "They should take care to plan out their route so that the challenges of finding their way do not further degrade their driving safety."
Uc notes that this study by itself does not provide an answer to the main question of when a person with Parkinson's disease should stop driving because of safety concerns. However, Uc hopes that all of the team's studies combined will get closer to that answer and be able to provide clear guidelines and predictive tests that accurately diagnose how safe a driver a patient with Parkinson's disease really is.
"At the end of the study, we hope to be able to define and measure indicators that predict the likelihood of crashes or unsafe driving in real life," Uc said. "We would like to develop a reliable and efficient set of tests to predict who is at risk. That information would then trigger interventions that might remedy the problems that can be remedied."
Researchers from the UI Carver College of Medicine, the UI College of Engineering, the UI College of Public Health and the UI Public Policy Center contributed to the study. In addition to Uc (principal investigator), the team included Matthew Rizzo, M.D., professor of neurology, engineering and public policy (co-principal investigator); Steven Anderson, Ph.D., associate professor of neurology; Robert Rodnitzky, M.D., professor and head of neurology; Jon David Sparks, in biostatistics; and Jeffrey Dawson, Sc.D., professor of biostatistics.
The study was funded by grants from the National Institute of Neurological Disorders and Stroke and the National Institute on Aging.
STORY SOURCE: University of Iowa Health Science Relations, 5135 Westlawn, Iowa City, Iowa 52242-1178