Driving with Cognitive Impairment

People with Alzheimer disease and even mild cognitive impairment may be dangerous to themselves or others on the road. Assessments of driving ability could be useful for evaluating whether or not people with impaired cognition should in fact drive at all.

A new study out of Toronto provides more information about driving ability in the cognitively impaired and how it can be assessed. The recent report appeared in the Journal of Alzheimer’s Disease.

The investigators, led by Megan Hird of the Neuroscience Research Program, St. Michael’s Hospital, Toronto, Canada, wanted The scientists performed a systematic review of the literature and meta-analysis of driving assessment methods. These included actual on-road driving, cognitive tests, and driving simulations. They assessed the predictive ability of the tests as well as specific areas of driving impairment in these individuals.

The review and meta-analysis included a total of 32 articles, including 1,293 subjects with Alzheimer disease, 92 subjects with mild cognitive impairment, and 2,040 healthy controls. Researchers used several different outcome measurements to test for driving ability, including on-road test scores, pass/fail classifications, errors; caregiver reports; real world crash involvement; and driving simulator collisions/risky behavior.

The study authors identified several statistically significant predictors of driving performance. These included global cognition, visuospatial function, attention, and executive function. Two tests were the most effective for predicting driving performance: the Trail Making Test part B and the Maze test. In the Trail Making Test part B, a subject is required to connect alternating encircled numbers and letters. The test measures visual attention and the ability to switch tasks. In the Maze test a subject draws through mazes of increasing complexity, without back-tracking. It is designed to measure planning and foresight.

The scientists further discovered that even people with very mild Alzheimer disease are more likely to fail a driving test compared to healthy control subjects.

Overall, Hird and colleagues concluded that, “The driving ability of patients with MCI and AD appears to be related to degree of cognitive impairment. Across studies, there are inconsistent cognitive predictors and reported driving outcomes in MCI and AD patients.”

Although the meta-analysis and systematic review provides some information about driving ability and cognition, more studies with greater specificity are still needed. For example, the effect of mild cognitive impairment on driving is not yet clear, possibly because studies of driving tend to focus more on Alzheimer disease-notable by the lower total subjects with mild cognitive impairment assessed in this meta-analysis compared to those with Alzheimer disease.

The authors also suggest that specific subject characteristics need to be assessed, namely “Future large-scale studies should investigate the driving performance and associated neural networks of subgroups of AD (very mild, mild, moderate) and [mild cognitive impairment] (amnestic, non-amnestic, single-domain, multiple-domain).”

Further prospective clinical trials may aid in the development of cognitive tests that can assess whether or not an impaired individual should drive. According to the American Academy of Neurology (AAN) Guidelines, a mini mental State Exam of 24 or less can indicate risk for unsafe driving. AAN guidelines also note that caregivers may be best to assess whether or not an individual with Alzheimer should drive. Future studies may concentrate on the predictive ability of direct cognitive tests, along with caregiver assessments.

Reference: Hird MA, et al. A systematic review and meta-analysis of on-road simulator and cognitive driving assessment in Alzheimer's disease and mild cognitive impairment. J Alzheimers Dis. 2016 May 11.