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Predictors of driving safety in early Alzheimer disease

From the Department of Biostatistics (J.D.D., E.D.), Division of Neuroergonomics, Department of Neurology (J.D.D., S.W.A., E.Y.U., E.D., M.R.), Department of Mechanical and Industrial Engineering (M.R.), and Public Policy Center (M.R.), University of Iowa; and VA Medical Center (E.Y.U.), Iowa City, IA.

Address correspondence and reprint requests to Dr. Jeffrey D. Dawson, Department of Biostatistics, University of Iowa College of Public Health, 200 Hawkins Dr., C-22 GH, Iowa City, IA 52242 jeffrey-dawson{at}uiowa.edu

Objective: To measure the association of cognition, visual perception, and motor function with driving safety in Alzheimer disease (AD).

Methods: Forty drivers with probable early AD (mean Mini-Mental State Examination score 26.5) and 115 elderly drivers without neurologic disease underwent a battery of cognitive, visual, and motor tests, and drove a standardized 35-mile route in urban and rural settings in an instrumented vehicle. A composite cognitive score (COGSTAT) was calculated for each subject based on eight neuropsychological tests. Driving safety errors were noted and classified by a driving expert based on video review.

Results: Drivers with AD committed an average of 42.0 safety errors/drive (SD = 12.8), compared to an average of 33.2 (SD = 12.2) for drivers without AD (p < 0.0001); the most common errors were lane violations. Increased age was predictive of errors, with a mean of 2.3 more errors per drive observed for each 5-year age increment. After adjustment for age and gender, COGSTAT was a significant predictor of safety errors in subjects with AD, with a 4.1 increase in safety errors observed for a 1 SD decrease in cognitive function. Significant increases in safety errors were also found in subjects with AD with poorer scores on Benton Visual Retention Test, Complex Figure Test-Copy, Trail Making Subtest-A, and the Functional Reach Test.

Conclusion: Drivers with Alzheimer disease (AD) exhibit a range of performance on tests of cognition, vision, and motor skills. Since these tests provide additional predictive value of driving performance beyond diagnosis alone, clinicians may use these tests to help predict whether a patient with AD can safely operate a motor vehicle.

AD = Alzheimer disease; AVLT = Auditory Verbal Learning Test; Blocks = Block Design subtest; BVRT = Benton Visual Retention Test; CFT = Complex Figure Test; CI = confidence interval; COWA = Controlled Oral Word Association; CS = contrast sensitivity; FVA = far visual acuity; JLO = Judgment of Line Orientation; MCI = mild cognitive impairment; MMSE = Mini-Mental State Examination; NVA = near visual acuity; SFM = structure from motion; TMT = Trail-Making Test; UFOV = Useful Field of View.

Supported by NIA AG 17717 and NIA AG 15071.

Disclosure: The authors report no disclosures.

Received August 4, 2008. Accepted in final form October 31, 2008.

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