Longitudinal driving performance in early-stage dementia of the Alzheimer type

OBJECTIVES: To longitudinally assess on-road driving performance in healthy older adults and those with early-stage dementia of the Alzheimer type (DAT). DESIGN: A prospective longitudinal study. SETTING: Large urban medical center and surrounding area. PARTICIPANTS: A sample of 58 healthy controls, 21 participants with very mild DAT, and 29 participants with mild DAT participated. DAT was diagnosed using validated clinical diagnostic criteria and staged according to the Clinical Dementia Rating (CDR) Scale. MEASUREMENTS: Healthy controls and individuals with very mild DAT and mild DAT were administered a standardized on-road driving assessment over repeated times of testing. RESULTS: Subjects in the CDR=1 group (mild DAT) had a faster rate of receiving a rating of not safe on the driving test than subjects in the CDR=0 group (healthy controls; log rank test, P=.006), and the survival function of the CDR=0.5 group (very mild DAT) fell between those of the CDR=0 and CDR=1 groups. A Cox proportional hazards model indicated a significant difference in survival functions between the CDR=0 and CDR=1 groups after baseline age was controlled for (P<.001). Cox regression analysis also indicated that baseline age was a significant risk factor for a rating of "not safe" (P=.002). CONCLUSION: This study provides longitudinal evidence for a decline in driving performance over time, primarily in early-stage DAT, and supports the need not only for driving assessments, but also for reevaluation of individuals with very mild and mild DAT.