A common clinical problem in aging is when should driving a motor vehicle be discontinued. When does driving become a significant safety hazard as cognition and motor skills decline?

The American Academy of Neurology recently published a Practice Parameter update: Evaluation and management of driving risk in dementia. This important review provides clinicians and family members with assistance in making an accurate and timely decision.

The authors of the guideline review research evidence of a variety of markers for unsafe driving risk. Some markers have more research support than others.

A standard assessment of driving ability is the on-road driving test. Mild dementia may not cause significant driving impairment. On study found that among those with mild dementia, 76% were able to pass an on-road driving test.

The Clinical Dementia Rating Scale appears to have the most research support for predicting unsafe driving. This scale scores six variables: memory, orientation, judgement/problem solving, community affairs, home and hobby activity and personal care. Subjects with a score of 0 on this test are generally not at increase risk of driving problems. Scores of 0.5 and higher have been tied to increased risk of accidents and increased rates of failure to pass an on-road driving test.

The Mini-mental status score is less clear in predicting driving impairment. Nevertheless the authors support using a score of 24 out of 30 as a cutoff for examining the need to discontinue driving.

The guidelines list a variety of markers for risk that have various levels of research support from highest (level A to lowest level C). This list is:

* Clinical Dementia Rating Scale score 0.5 or higher (Level A)
* Caregiver rating of patient’s driving ability as marginal or unsafe (level B)
* Recent history of traffic citations (Level C)
* Recent history of accidents (Level C)
* Reduced driving mileage–less than 60 miles per week (Level C)
* Self-reported avoidance of driving situations (Level C)
* Minimental status scores of 24 or less (Level C)
* Aggressive/impulsive personality behaviors (Level C)

Interestingly, the patient’s self-rating of safe driving ability is not useful. A patient with dementia is unable to accurately report their driving ability.

More comprehensive neuropsychological testing does not appear to provide additional prognostic information. It can be helpful in estimating severity of dementia which does relate to risk.

For those with markers of risk, family should support alternate methods of transportation and urge voluntary surrender of driving privileges. For those at high-risk who refuse, referral to the local state Department of Motor Vehicles or a professional driving evaluation should be considered.

This guideline paper provides a patient and a family/caregiver questionnaire that is helpful in assessing the at-risk driver. Other scales are also included.

William Yates is a family physician who blogs at Brain Posts.

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