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Parkinson’s impairs driving skills, safety

Thursday November 30, 2006

Nov 23, 2006 (Reuters) - People with Parkinson’s disease have difficulty spotting traffic signs and roadside landmarks while driving, and are more likely to make safety errors on the road, a new study shows.

These difficulties are related to the cognitive and visual effects of Parkinson’s rather than better-known motor symptoms such as tremor, investigators say.

People with Parkinson’s often continue to drive, and some continue to drive well and safely, but there is currently no reliable way to test which ones will fare better behind the wheel, Dr. Ergun Uc of the University of Iowa in Iowa City noted in an interview with Reuters Health. He is leading a five-year, National Institutes of Health-funded study of Parkinson’s patients with the goal of developing a system to predict their driving abilities.

In the current investigation, which is part of the larger study, Uc and his colleagues had 79 drivers with Parkinson’s disease and 151 healthy older people complete a battery of tests to measure their visual, cognitive and motor abilities.

Study participants then completed a 16.7-mile course in a Ford station wagon equipped with a variety of sensors and cameras. They were asked to look for and report the presence of traffic signs and restaurants about a minute before these landmarks appeared. They were also monitored for unsafe driving behaviors such as moving into another lane or onto the road shoulder or slowing or stopping inappropriately.

On average, the Parkinson’s patients fared significantly worse on the road tests than the control group, the authors report in the Annals of Neurology.

For example, they made .64 safety errors per mile, which jumped to nearly two such errors per mile when they were asked to identify landmarks as they drove.

The control group averaged 0.15 errors per mile while driving, and 0.45 errors per mile while looking for landmarks

Parkinson’s patients were able to identify 47.8 percent of the landmarks and traffic signs, compared to 58.7 percent for the control subjects. Seventeen percent of the Parkinson’s patients made no safety errors at all, however.

Uc also noted "the cognitive and visual tests are more predictive of driving errors and driving performance than the motor function."

The findings clearly show that people with Parkinson’s drive less safely than their age-matched peers without the disease, and that vision tests are not enough to gauge their driving ability, Dr. Nancy J. Newman of the Emory University School of Medicine in Atlanta notes in an editorial accompanying the study.

"The question remains whether early identification and application of rehabilitation targeted to those aspects of driving most troublesome for this group of patients would improve their driving performance and prolong their independence, without risking their safety and the safety of others," she writes.