P2-130: Amyloid imaging and cerebrospinal fluid biomarkers predict driving performance in preclinical Alzheimer's disease

The number of older adults in the U.S. is expected to double within the next 40 years, with a dramatic increase in the number of older adult drivers. During the long preclinical stage of Alzheimer disease (AD), AD pathology is present without notable cognitive or functional impairment, although whether there are subtle deficits that may impair complex behaviors such as driving has not been well-studied. The purpose of this study was to examine whether AD biomarker levels (amyloid imaging, cerebrospinal fluid) are associated with driving performance in cognitively normal older adults. We recruited 134 participants with normal cognition (Clinical Dementia Rating 0), aged 65 years and older. Participants took part in an on-the-road driving test, clinical and psychometric assessments, Pittsburgh compound B (PIB) amyloid brain imaging, and cerebrospinal fluid (CSF) collection. We examined whether higher and lower values of each of our biomarker variables (mean cortical binding potential [MCBP] for PIB, and CSF Aβ42, tau, ptau181, tau/Aβ42, ptau181/Aβ42) were associated with the total number of errors made on the driving test. For each variable, a median split was used to assign participants to either a “lower” or “higher” group based on the measured biomarker value. General linear models (adjusted for age, education, and gender) were used to test whether the number of total driving errors differed for each of the dichotomous biomarker variables. The analyses were repeated treating the biomarker variables as continuous. Of the first (N=121) participants who had PIB (N=116) and CSF (N=82) data available for analysis, 52.1% were women and 9.1% were African American. Their mean age and education were 72.6 (SD=5.1) and 16.1 (SD=2.6) years respectively. Participants in the groups with higher MCBP for PIB and higher CSF tau/Aβ42 and ptau181/Aβ42 values made approximately 2.5 more driving errors, on average, than those in the groups with lower values (Table 1). In the analyses treating the biomarkers continuously, only the effect of MCBP for PIB was significant (p=.015). These preliminary results suggest that cognitively normal older adults with more AD-like abnormal biomarker values have worse driving performance.