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Evidence-Based Reviews

Driving with dementia: How to assess safety behind the wheel

Cognitive tests are not sufficient to evaluate driving fitness in patients with Alzheimer’s disease

Vol. 7, No. 12 / December 2008

Mr. D, age 75, presents to your office with a 5-year history of gradually declining memory. His wife reports he is having difficulty with word finding, managing his finances, and shopping, and he needs supervision when using the stove. Nonetheless, he enjoys playing golf and drives himself to the golf course 3 times a week. He is compliant with his chronic medical therapy for hypertension, hypercholesterolemia, and asthma.

Patients with dementia who continue to drive pose a potential danger on the road, worry their families, and present challenges to clinicians. Most people would agree that patients with moderate or severe dementia should not drive, but a careful evaluation is required to assess whether a patient such as Mr. D with mild dementia remains fit to drive.

This article explores how dementia exacerbates age-related changes in driving ability and discusses how to assess driving in patients with dementia. Our goal is to help clinicians sort through data from in-office physical and cognitive assessments, family caregivers/informants’ reports, and (when available) on-road testing. We also discuss:

  • guidelines for assessing older drivers that can help balance patients’ need for autonomy with public safety
  • strategies for discussing driving cessation with patients and their families.

Driving: A privilege, not a right

Driving is central to older adults’ autonomy, and >75% of persons age ≥75 rely on driving as their primary mode of transportation.1 Driving cessation in this population has been associated with a 3-fold decrease in out-of-home activity2 and a 2.5-fold increase in depressive symptoms.3 Nonetheless, some 4.5 million Americans have Alzheimer’s disease (AD),4 and dementia poses a substantial risk to safe driving.

Although driving must be sacrificed when personal and public safety is at risk, most physicians perceive an uncomfortable conflict of interest between patient confidentiality and public safety.5 Assessing driving safety of patients with dementia can undermine the doctor-patient relationship and pose hardships for patients.

Mr. D has a 5-year history of memory problems that affect his daily functioning, yet he continues to drive. A longitudinal study of persons with dementia found that among the 29% who were driving at baseline, more than one-half were still behind the wheel 2 years later.6

Age and driving safety. Even in the absence of dementia, driving ability declines with aging (Tables 1 and 2).7,8 Older persons may self-regulate and restrict their driving to shorter distances, with fewer trips at night, on high-speed roads, or in unfamiliar situations. Their driving is rarely aggressive and they are unlikely to speed, but they may drive more slowly than other traffic.7,8 Although the overall rate of motor vehicle collisions declines with age:

  • the rate of collisions per mile driven increases after age 659
  • drivers age >65 have the highest fatality rate per mile driven among adults age ≥25.10

A dementia diagnosis is not sufficient to withdraw driving privileges, according to American Medical Association (AMA)/National Highway Traffic Safety Administration (NHTSA) guidelines. These recommend that you base decisions on the individual’s driving ability, and—when you have concerns—factor in a focused medical assessment and formal assessment of driving skills.10

Table 1

Age-related changes that may affect driving fitness

Decreased physical capabilities, including declining muscle tone, flexibility, and reaction time

Decreased hearing and visual acuity

Increased fragility, resulting in longer time to heal should injuries occur

Increased medication use with possible side effect of drowsiness

Source: References 7,8

Table 2

Older drivers’ common traffic violations leading to crashes*

Failure to obey traffic signals, including stop signs and red lights

Unsafe left turns (driver may inaccurately judge speed of oncoming vehicle)

Inappropriate turns (such as difficulty judging distance from oncoming cars, wide or narrow turns, or not timing the turn correctly with traffic lights)

Unsafe passing

Failure to yield

* These errors often lead to multivehicle accidents
Source: References 7,8

CASE CONTINUED: Cognitive deficits quantified

You perform a Mini-Mental State Examination (MMSE). Mr. D scores 24/30, losing 1 point for orientation, 2 points for attention, 2 points for recall, and 1 point for copying. This score, along with his history, indicates mild dementia, although he claims he is a safe driver. On further cognitive testing, Mr. D completes the Trails A test in 90 seconds and Trails B test in 250 seconds (well below 1.5 standard deviations of the norm for his age and education).11 On the clock-drawing task, he drew a poorly organized clock, with unequal spaces between numbers and hands pointing to “10” and “11” instead of properly indicating “10 after 11.”

Mr. D and his wife live in a rural area, 5 miles from the nearest grocery store. His wife never drove, and she relies on him for weekly shopping trips and to drive her to her bridge club. She denies any problems with his driving but states, “Other drivers have become so aggressive; they’re always honking at him.” Their daughter denies that Mr. D has driving problems but admits that for the last 2 years she has refused to allow her child to ride in his car.

Focused in-office assessment

Information to assess driving ability can come from the patient, family caregiver/informant, and clinical judgment. Patients with dementia are notoriously inaccurate in self-reported driving ability, either for lack of insight or as a testament to the importance of driving to their autonomy. Caregivers often are more accurate in describing a patient’s driving, but other agendas may color their responses.

In a study of patients with very mild or mild AD, 94% reported themselves as safe drivers, whereas on-road driving instructors rated <50% of drivers in these groups as safe. Caregivers were better able to classify driving performance, but 36% of their ratings were incorrect.12

Cognitive assessment. To assess older drivers’ cognition, AMA/NHTSA’s Guide to Assessing and Counseling Older Drivers recommends the Trail-Making Test, Part B and the clock-drawing test.10 The Canadian Medical Association suggests the MMSE.13 Both guides say that abnormalities in these tests indicate a need for more detailed testing, including referral to specialized driving assessment and retesting at regular intervals (Algorithm). Retest patients with mild dementia at least every 6 months or sooner when dementia severity increases noticeably14 (Box 1).6,15

The MMSE is widely used to screen for cognitive impairment and identify dementia or delirium, but it is not a diagnostic tool or proxy driving test. A patient with dementia may produce a high MMSE score and yet be an unsafe driver. For example, well-educated patients or those with vascular or frontotemporal dementia may retain cognitive abilities as measured by the MMSE until later in the disease.

Considerable effort has been put into developing tools to help clinicians quickly and accurately differentiate safe from unsafe drivers by assessing cognition. Unfortunately, no consistent link has been found between cognitive test results and driving outcome measures. A systematic review of office-based predictors of fitness to drive in dementia found 5 studies showing an association between MMSE scores and driving and 5 studies showing no such association.16 Thus, although the AMA/NHTSA guide recommends the MMSE, Trails B, and clock-drawing tests, cognitive tests—including these—are not sufficient to assess driving ability.

Severity of dementia. International consensus groups have attempted to create guidelines for patients with dementia who drive. American, Canadian, and Australian groups suggest that a diagnosis of moderate to severe dementia precludes driving, and the driver’s licenses of persons with these conditions should be revoked.17

In general, AD is considered severe when the MMSE score is <10 or the patient becomes dependent on a caregiver for survival.18 AD of moderate severity is more difficult to define, but a Canadian consensus conference suggested a practical approach: Patients with AD would be considered to have moderate to severe dementia and should not drive when they cannot independently perform multiple instrumental activities of daily living or any of the basic activities of daily living.19

Some dementias may impair driving more quickly than AD does. For example, hallucinations may occur early in Lewy body dementia, as may impulsivity in frontotemporal dementia and motor impairment in vascular dementia.

Box 1

Case report: AD-related behavioral symptoms

Mrs. Y visits your office for a follow-up regarding mild Alzheimer’s disease (AD), which was diagnosed 2 years ago. She passed an on-road test 3 months ago and has an Mini-Mental State Examination score of 24/30. Over the last month she has become depressed, with insomnia and mild psychomotor retardation. She occasionally has hallucinations.

Behavioral and psychological symptoms such as agitation, aggression, hallucinations, apathy, depression, and anxiety are common neuropsychiatric sequelae of AD. Little is known about the risks these symptoms pose to road safety, but we recommend that clinicians strongly consider the potential for impaired driving.

In a longitudinal study, cognitive impairment and behavioral disturbances—especially agitation, apathy, and hallucinations—were strong predictors of driving cessation among patients with dementia.6 Furthermore, a case crossover study of patients with dementia found a 54% increase in risk of motor vehicle collisions associated with the use of psychotropic medications.15

Consider all aspects of the patient’s clinical status, including neuropsychiatric symptoms, psychotropic medications, comorbid medical conditions (including hearing and vision impairment), and concomitant therapy for medical conditions. Any could change a safe driver with mild dementia into an unsafe driver.

Algorithm: 3 options for drivers with dementia, based on in-office assessment
* Observe legislation or statutes that address reporting unsafe drivers to the department of motor vehicles or ministry of transportation

On-road driving tests

Because some individuals with mild dementia can drive safely for extended periods, international recommendations for assessing the driver with dementia emphasize on-road driving tests.10,13,2022 American10 and Canadian guidelines13 suggest that a dementia diagnosis is not sufficient to withdraw licensure.

A formal driving assessment is necessary to establish road safety for patients with mild dementia except when the need for license withdrawal is evident, such as when the patient has:

  • a history of major driving problems (such as crashes or driving the wrong way on a highway)
  • significant contraindications to driving on the history or physical examination (such as severe inattention or psychosis).

Challenges of on-road testing. On-road tests may be the gold standard, but they are not without clinical problems.

Need to retest. Because almost all dementias are progressive and driving skills deteriorate over time, most guidelines recommend periodic retesting. For patients with dementia who pass on-road evaluations, limited evidence supports retesting every 6 months.14 Take an individual approach, however, because of the various rates at which the dementias progress.

Testing vs real world conditions. Structured on-road testing is not equivalent to unstructured real-world driving, in which the patient often must navigate without instruction or assistance.

Rural vs urban driving. Road tests conducted in urban areas assess skills associated with complex conditions and the need to respond quickly to crises. They might not assess as well rural driving, which requires sustained attention on monotonous roads.

Inaccessibility. Cost and lack of availability of on-road tests, particularly in rural areas, limit the number of patients whose performance can be evaluated.

CASE CONTINUED: Distressing results

Mr. D has a history of decline in cognition and function, objective cognitive difficulties, and a subtle history of driving problems. You refer him for a specialized on-road test, and the report indicates that he failed. Errors included wide turns, driving too slowly, getting caught in an intersection twice during red lights while attempting to turn left, driving on the shoulder, and failing to signal lane changes. You review the results with Mr. D and his wife and recommend that he cease driving immediately.

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