Driving and dementia

Corroborated history

Assessment of driving safety begins with a careful corroborated history to obtain an accurate report of family member concerns and documentation of previous motor vehicle accidents or near accidents. This corroborated history can be obtained in the context of a full discussion with family about all medical and safety issues, with permission usually sought from the patient when discussing any issues with family. The family member should be interviewed alone, allowing for safe disclosure of any driving concerns. A history of a motor vehicle crash within the previous 2 years has been shown to be a strong predictor of future motor vehicle crashes.¹⁶ When family members do raise concerns about driving safety, they are often accurate and their concerns should be strongly considered²³; however, lack of concern might not always reflect low driving risk. Drivers with dementia and their family members might not recognize decline in driving-related abilities or might underreport concerns, possibly owing to personal bias.^24,25 Corroborated history can also help to determine the degree of functional impairment in instrumental and basic activities of daily living due to cognitive difficulty^9,26 (Table 1¹⁰) as a proxy for severity of the dementing illness. Consensus among national guidelines is that those with moderate or severe dementia should not drive; in the Canadian Medical Association guidelines,²⁶ this is defined by a new loss of ability to perform 2 or more instrumental activities of daily living or any basic activity of daily living on the basis of cognitive difficulties.

Cognitive testing

Several international guidelines have recommended use of the TMT-B to assess driving safety. The TMT-B measures motor processing speed, executive functioning, and cognitive flexibility in switching attention between competing sets of stimuli. A systematic review concluded that there is support for using TMT-B cutoffs of 3 minutes for completion or 3 or more errors¹¹—the 3 or 3 rule (Table 2).¹⁰ The TMT-A,²⁷ a task that measures motor processing speed, might also be helpful in discriminating between safe and potentially unsafe cognitively impaired older drivers. A recent study demonstrated that inability to complete the Trail Making tests within a reasonable time frame (ie, TMT-A > 48 seconds, TMT-B > 108 seconds) might suggest the need for further driving evaluation.²⁸ Both the TMT-A and TMT-B are available at www.healthcare.uiowa.edu/igec/tools/cognitive/trailMaking.pdf or www.rgpeo.com/media/53150/trails%20a%20and%20b.pdf.

Guidelines have recommended the administration of other cognitive screening tests, such as the Mini-Mental State Examination (MMSE) and the clock-drawing test. Scores on the MMSE have not been shown to be predictive of driving risk^16,17 or motor vehicle crashes¹⁶ in drivers. However, impairment in the copying of the intersecting pentagon task in the MMSE, but not the MMSE score itself, has been associated with driving cessation in older adults.²⁹ Indeed, a meta-analysis of neuropsychological tests has suggested that tests of visuospatial skills might be the most relevant to driving abilities.⁶ The clock-drawing test has also been shown to predict performance on a driving simulator.³⁰ It is unfortunate that the complex methods used to score the clock-drawing test in research are rarely used in front-line clinical care, where the gestalt approach of dichotomizing results into good or bad is usually used. Further research is required to develop scoring methods that are feasible in the context of busy clinical practice and that are correlated with crash risk. Recently, a study¹⁷ demonstrated that in cognitively impaired older adults, the MoCA²⁰ score might have better predictive value for driving outcome than that of the MMSE. In that study, a MoCA score of 18 or less in cognitively impaired individuals was associated with greater likelihood of failing an on-road driving assessment, although its predictive ability was not strong enough to recommend its use as the sole instrument for identifying unfit drivers.¹⁷

Figure 1 summarizes the corroborated history and cognitive testing elements that might aid in a physician’s decisions to refer for comprehensive on-road driving evaluation and to report to transportation authorities in accordance with provincial requirements.²⁶ The greater the number and the greater the severity of worrisome findings, the more concerned the physician should be that the patient might be at higher risk of a motor vehicle crash. Reporting to transportation authorities might be warranted, as is discussion of the option to arrange for a comprehensive on-road driving evaluation as the fairest means of determining driving safety. It should be noted that factors other than cognition might affect driving safety and must also be considered in the assessment of any older driver. These can include the presence of physical limitations, visual impairment, excessive alcohol consumption, and other comorbid conditions; these are described in detail elsewhere.^8,26

• Download figure
• Open in new tab

Figure 1.

Checklist of considerations in driving safety

^*Ask the patient and a family member separately.

Communication and follow-up

Physicians in most Canadian jurisdictions are legally mandated to report medical findings that could affect fitness to drive. Even in provinces with discretionary reporting, Canadian guidelines²⁶ recommend that physicians err on the side of reporting any potentially medically unfit driver to permit transportation authorities to investigate further and to prevent potentially avoidable patient, caregiver, and bystander morbidity and mortality. However, reporting to transportation authorities might compromise the physician-patient relationship^31,32 and is identified as an important barrier to care^2,4 for front-line clinicians. In disclosing concerns about driving safety to the person with dementia and their family members, the need for tactful communication and sensitivity cannot be overstated. Dementia is a progressive, terminal illness associated with feelings of shame, rejection, social isolation, and loss of a sense of control.³³ Driving discussions are emotionally charged because the ability to drive is associated with independence and personal identity.³⁴ Loss of driving ability has been associated with social isolation³⁵ and an almost doubled risk of depressive symptoms.³⁶ A person-centred approach³⁷ is essential, considering the perspectives and needs of the individual and exploring transportation alternatives that might help the person to maintain mobility and social functioning.

For persons with mild dementia who are still able to drive, guidelines recommend regular reassessment of driving safety every 6 to 9 months.²⁶ Ideally, for all persons with a diagnosis of dementia there should be early discussion of the eventual need to stop driving. Communication that occurs over time allows older persons the opportunity to reflect on the process of driving retirement and to plan for transportation alternatives.³⁴ Resources to assist with this discussion and planning are available in the Driving and Dementia Toolkit for Patients and Caregivers (www.rgpeo.com/media/30422/d%20%20d%20toolkit%20pt%20crgvr%20eng%20with%20hyperlinks.pdf) and the Driving and Dementia Toolkit for Health Professionals (www.rgpeo.com/media/30695/dementia%20toolkit.pdf).^38,39 Primary care physicians are uniquely positioned to have trusting, sensitive conversations with their older patients about driving safety concerns and the need for future transition to alternate forms of transportation.³⁴

Future research should be directed to the challenging area of assessing driving safety in persons with mild cognitive impairment,⁴⁰ as well as to the development of a composite battery of office-based tests with valid, usable cutoff scores that reliably screen for driving safety in cognitively impaired persons that can be feasibly administered in the clinical primary care setting.¹⁴ Until then, clinicians must continue to consider many factors when determining if cognitive concerns affect driving safety, balancing the need to respect individual autonomy with maintaining patient and public safety.