PD disease markers - unreliable indicators of driving performance

Unsafe driving in individuals with PD cannot be predicted using clinical disease markers or a patient's self-rated driving performance.Australian investigators report that drivers with Parkinson's disease (PD) are less safe than age-matched controls, and that clinical disease markers cannot reliably predict driver safety. They say that it is also unrealistic to rely on a patient's own judgement, as there was no relationship between self-rated performance and driver safety rating in their study. Twenty-five drivers with PD and 21 age-matched controls were included in the Queensland study. Participants were asked to answer a questionnaire related to driving experience and habits, perceived difficulties with specific situations, and physical limitations related to PD. Driving performance was assessed by a driving instructor and an occupational therapist after each participant drove along the same route under a combination of directed instruction and self-directed navigation.The authors report, "The drivers with PD made significantly more errors than controls in lane keeping and lane changing, reversing, parking, monitoring of their blind spot, and negotiating traffic light controlled intersections. The driving instructor also had to intervene significantly more often for drivers with PD." They suggest that these errors may be related to aspects of PD such as decreased motor control skills and impaired visuo-spatial processing, sequence control and planning.Five of the 25 drivers with PD received an assessment indicating that they should cease driving, after the instructor had to take action to avoid an incident or the driver hit a significant object. Further, 14 drivers with PD (compared to 5 of the 21 controls) received a score that indicated they would have failed the Queensland driving test.Although driver safety ratings were significantly correlated with time since diagnosis, they were not related to clinical markers, such as on time UPDRS, the Hoehn and Yahr scale, or levodopa dosage. Importantly, there was also no correlation between a driver's self-rated driving performance and their safety rating in either the participants with PD or the controls. Reference...