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From the Quality Standards Subcommittee of the American Academy of Neurology.
Address correspondence and reprint requests to The Quality Standards Subcommittee of the American Academy of Neurology, Wendy Edlund, 1080 Montreal Avenue, St. Paul, MN 55116.
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Article Abstract |
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 Top. Article Abstract IntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Key words: AD—Dementia—Driving—Automobile—Practice guideline.
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Introduction |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Background. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Justification. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Many individuals with early AD drive. As the dementia progresses, driving becomes impaired. Rational recommendations about driving by patients with AD can be made by physicians using the risk of a crash and the driving limits set by law, provided the physician understands the limits of current information. It would be inappropriate to restrict driving by one group on the basis of age or disease, while allowing another group with the same or a higher accident rate to continue to drive. On the other hand, the expected changes in driving skills with maturation (in the case of young drivers) and with degenerative decline (in drivers with AD) may influence whether restrictions are considered appropriate in different groups even if the risks in these groups are initially similar. The first is expected to improve, while the latter is expected to worsen over time.
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Description of the process. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Articles published before 1966 and articles not found on MEDLINE were identified by reviewing the references in each of the studies found through the MEDLINE search using the criteria listed above. Articles were excluded if they were only reviews, editorials, or opinions.
From the articles identified using the search criteria listed above, we extracted the following data: cohort size, characteristics of study subjects, selection method of study subjects and controls, blinding, dementia severity measurement, and driving (crash or accident) assessment. To compare studies using different indices of dementia severity, we used the conversion table proposed by Reisberg, et al. to convert to the Clinical Dementia Rating (CDR) scale (table).2,3 A CDR of 0.5 is roughly equivalent to a Mini- Mental State Examination (MMSE)4 score of 25, while a CDR stage 1 is roughly equivalent to a MMSE of less than 25 but greater than 19.2 The use of CDR stage was chosen over the MMSE because it is a functional assessment. The MMSE was developed as a screening tool for dementia and it does not take into account a functional assessment of the subject.
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Scientific reports. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Crash statistic studies in drivers with AD. In 1963, Waller reported the results of a review of driving records of all drivers in California requiring a medical review. In his 1967 follow-up study, Waller reported the results of a survey mailed to residents of a retirement community (Class IIb).5 Ten percent of the residents were randomly selected for the mailing. The return rate was 53.7%. Eighty-two subjects classified as "senile" were compared to 83 cognitively normal older individuals. He did not publish the definition of the "senile group." The accident rate per million vehicle miles traveled is the standard used to measure accidents as reflected by driving exposure. Accident rates without data on exposure do not allow accurate comparison of groups of drivers. Driving exposure data were collected in Waller’s study, unlike most of the studies that were reviewed. The "senile" group reported 19.3 MVA/MVMT while the cognitively intact healthy elder group had 12.1 MVA/MVMT (relative rate = 1.56; 95% CI could not be calculated from the information in the article). This rate is high demonstrating an increase in the true accident rate of "senile" drivers when compared to cognitively intact elder drivers.
In a 1988 questionnaire study administered to 30 patients with probable AD and to their spouses/caregivers and to a community-based control group.6 (Class IIb), crashes were recorded over the time course from the onset of dementia (average 5.5 years). The mean duration of dementia was 4.0 years (±1.8) at the time of the first crash. The average MMSE score was 19.9 (±6.3) corresponding to a CDR of 1.0 (RR = 7; 95% CI: 5.26 to 35.2). The eight-fold increase in the crash rate for the group with Alzheimer’s implies a greater risk of crashes compared to other drivers.
In 1988, a 20-item screening questionnaire was administered to the caregivers of 72 consecutive patients referred to a dementia clinic.7 The subjects had either AD (National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer’s Disease and Related Disorders Association [NINCDS-ADRDA] criteria, 53%), multi-infarct dementia (8%), a combination of AD and multi-infarct dementia (4%), other causes of dementia (9%), or dementia of unknown etiology (26%). A control group was not used. Driving exposure was not determined (Class IIb). Thirty per cent of their subjects were involved in motor vehicle accidents after the onset of dementia (average duration of 3.4 ± 2.4 years). An additional 11% were thought by their caregivers to have caused an accident. This study also demonstrates the risk of accidents and dangerous driving behavior by those with AD that still drive.
In 1991 a structured interview was used to assess driving behavior and crashes in 522 consecutive referrals to a dementia clinic8 (Class IIb). A control group was not included nor was there information on driving exposure that would allow comparison to published crash rates in elderly controls. They reported that 21 (22.6%) of the 93 subjects who were still driving at the time of the interview, had had a single or multiple car motor vehicle accident in the six months before the interview. Again, driving appears to be hazardous in this group.
In a 1992 study, a questionnaire was administered to 67 drivers with AD and to their caregivers, and compared to the results with 100 elderly controls recruited from the community9,10 (Class IIa). An accident rate was calculated based upon exposure. Nineteen drivers with AD (CDR 0.5) were still driving at the time of the study. Their accident rate was 26.6 MVA/MVMT (95% CI: 0.6 to 69.9) compared to 8.5 MVA/MVMT (95% CI: 5.3 to 13.8) for the 98 controls who were still driving at the time of the study (RR = 3.13). The results of this age-matched cohort survey are consistent with the studies reviewed above.
Drachman et al. surveyed the driving habits of patients who met the NINCDS-ADRDA criteria of possible or probable AD11 (Class IIa). Patients with AD and their caregivers were interviewed in seven AD research centers. Their responses were compared to those of normal elders recruited by the same centers. Subjects with dementia were matched by gender and age, oldest to oldest, next oldest to next oldest, etc. at each site. There was a linear increase in the rate of crashes among drivers with AD over the 6-year period studied. CDR staging was not used, but given the short time that AD was reported in these patients, most of their subjects would be expected to be CDR 0.5 to CDR 1.0. There was a 2.3 fold difference (95% CI: 1.11 to 10.2) in the relative risk of crashes between the two groups. The authors acknowledged that although the number of crashes per year was greater in the drivers with AD when compared to the controls, the crash rate per year was still less than that reported for 16 to 24-year-old drivers. This study has two major methodological shortcomings: inadequate matching of subjects and controls and lack of a measurement of driving exposure. While similar percentages of each group were reported for the ranges of <5,000 miles, between 5,000 and 10,000 miles, and >10,000 miles of driving per year, the accident rate per million vehicle miles of travel can not be calculated without a comparison of driving exposure between the groups. The results of this study are similar to those of the other studies.
A 1995 review of driving records was performed of patients referred to a dementia clinic, compared with the records to controls, matched for gender, age, and place of residence (Class IIa).12 Because there was a single insurer for the Province of British Columbia, all records for insured drivers could be reviewed. Of 165 patients (86 with probable and 68 with possible AD by NINCDS-ADRDA criteria; 11 with dementia but unlikely to have AD) 61 (37.0%) had crashes compared to 25 (15.1%) controls. The control group was matched to the subjects by age, gender, and location of residence in the province. Estimates of miles driven by each group were not obtained. They calculated a crash rate based on the number of months of driving after the diagnosis was made. The subjects with AD had 0.15 crashes per year compared to 0.06 crashes per year for the matched controls (RR = 2.26; 95% CI: 0.88 to 5.97). Though this study is limited by the comparison of crashes per year instead of the standard of accidents per miles driven, the results agree with other studies of accident rates.
A 1996 review compared the driving records in police files of 143 licensed drivers with AD who were either currently driving or had driven within five years of an evaluation at the Alzheimer’s clinic at the University of Michigan13 to five records matched by the Michigan Office of the Secretary of State by gender, age (±6 years) and county of residence (Class IIa). The average MMSE of the subjects with AD who were still driving, and those who had stopped driving, would place them in CDR stage 0.5. The reported accident and traffic violation rates were similar for the two groups. However, driving exposure was not used to calculate the accident rate, even though the authors had collected information on the amount of recent travel (kilometers per week) of those who were still driving. They hypothesized that if exposure were taken into account, there would have been an increase in the crash rate for the drivers with AD drivers, but the measured RR = 1.0 (95% CI: 0.986 to 1.015) suggested no significant difference. Thus this is the only study cited so far that did not show more crashes for the drivers with dementia than for the normal population in the study.
Almost all of these studies demonstrate an increased crash rate for drivers with AD.
Driving performance studies in drivers with AD. The first performance test of driving in a group of drivers with mild dementia (presumably most had early AD, CDR 0.5) compared to drivers with diabetic retinopathy, multi-infarct dementia and normal elders was reported in 199514 (Class IIb). The authors used an on-the-road, 2.7 mile fixed course test on the grounds of a Veteran’s Administration Medical Center. Investigators experienced in assessing driving rated the driver’s performance. They were blinded to the clinical status of the drivers. The drivers with mild dementia performed at a significantly lower level than the control group and the diabetic retinopathy group. Unfortunately, pass/fail criteria for the on-the-road test were not included in the article. Without pass/fail criteria, the relative rate and confidence interval could not be calculated, despite the significantly lower level of driving performance for the drivers with dementia.
In a 1997 study the driving evaluation of 19 drivers with mild dementia was reported (Class III).15 The drivers underwent extensive testing that included an on-the-road driving assessment. Only seven of the subjects passed. The passing rate of safe drivers was not given. This study also suggests substandard driving performance by drivers with AD.
In 1996 Rizzo et al. used a high fidelity driving simulator, with six degrees of freedom, to assess the driving ability of 21 drivers with AD in comparison to 18 elderly controls without dementia (Class IIa).16 The drivers with dementia (CDR 0.5 and 1.0) had twice as many "close calls" as the normal drivers. Six of the drivers with dementia were involved in crashes on the simulator, but none of the controls were. The drivers with dementia also had significantly more lane boundary violations (going over the yellow or white lines), but specific data were not given. This is unfortunate in that lane boundary violations are a categorical measurement of the standard deviation of lane position, a continuous measurement of tracking error when a driver is attempting to stay in their lane. Driving under the influence of alcohol at a BAC of 0.08% is associated with a standard deviation of lane position of 1.04 feet, while driving with a BAC of 0.1% is associated with a standard deviation of lane position of 2.0 feet.17,18 If the data on lane boundary violations were included in the article, a direct comparison to the equivalent impairment associated with driving under the influence of alcohol could have been made. This observational cohort study reported significant errors by drivers with AD on relatively simple components of the driving task that either caused crashes or near misses.
Hunt et al. performed an on-the road-test of driving ability of drivers with AD, CDR stage 0.5 (n = 36) and 1.0 (n = 29), compared with that of normal elders (n = 58) (Class I).19 They used a preliminary closed course to familiarize the subjects with the controls and handling of the test vehicle. The subjects then drove a fixed course on the open road. Driving ability was judged by driving instructors and a physical therapist with experience in the evaluation of handicapped drivers. Both were blinded to the cognitive abilities of the test subjects. Two of the controls failed the open road test compared with seven (19%, RR = 5.64; 95% CI = 4.4 to 31.3) with very mild dementia (CDR 0.5), and 12 with moderate dementia (CDR 1.0) (41%, RR = 12; 95% CI = 9.1 to 62.1).
These four studies demonstrate significant impairment in the driving ability of drivers with AD.
Driving task testing in drivers with AD. The flaws noted in the above studies, combined with the relatively minor motoric problems in mild to moderate AD, have led some investigators to concentrate on visual perception of drivers with AD. This is based upon the attentional model of driving performance proposed by Parasuraman and Nester.20-22
Ball et al. investigated visual processing in a group of 302 drivers in Alabama who were stratified based on the number of recent crashes (Class IIa).23 The main visual assessment was the Useful Field of View test (UFOV). This test measures the speed and accuracy of detecting visual stimuli within and adjacent to central vision. A decrease in the UFOV by 40% or more and impaired mental status (defined as a score > 9 on the Mattis Organic Mental Status Syndrome Evaluation) together accounted for 28% of the variance in the number of crashes in their study population. However, in their follow-up study, mental status at the time of the initial study was not predictive of crashes during the 3 years of follow-up (Class I).24 Thus, although visual processing combined with impaired mental status can account for a substantial amount of the variance in crash rates in an elderly population, the combination did not predict future crashes.
In a 1998 study the ability to recognize traffic signs by drivers with early AD was compared to normal aged controls (Class IIb).25 The test used was the standard 10 traffic sign test administered by the Indiana Bureau of Motor Vehicles as part of the drivers license renewal test. Twenty-one of 37 subjects with AD failed the test (
6 correct answers) versus 5 of 47 control subjects. (RR = 5.5; 95% CI: 3.1 to 18.1) These drivers would have had their license revoked as a result of their failure. Thus, we can use this study as an application of a governmental pass/fail test on a selected population. The mean MMSE scores of the subjects with AD were 20.2 for those who failed the test and 25.1 for those who passed, placing the groups in CDR stage 1 or 0.5 respectively. The high rate of errors on a simple traffic sign recognition test agrees with the driving errors reported in the performance studies and in the tendency for drivers with dementia to become lost as cited in the articles above.
These three studies demonstrate significant problems with visual processing in drivers with AD.
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Statement of the evidence. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Almost all of the reports that met the inclusion or exclusion criteria of our analysis found that cognitively impaired drivers fared worse than controls. However, most of the accident statistics research on drivers with AD have not taken driving exposure into account, have not relied on blinded evaluators, and have not included an adequate sample size. It is also difficult to compare the severity of dementia across studies. Therefore, whether the drivers with AD in most of the studies we reviewed really had an accident rate greater than society tolerates in younger drivers (age 16 to 19 years) is moot, but there is no doubt that the accident rate in the group with dementia is high. As to the relationship of degree of dementia to the accident rate, the CDR stages are based upon many levels of functioning of a patient with AD. Unfortunately, conversion of other scales to an equivalent of CDR stage 0.5 requires the combining of several dissimilar groups: mild cognitive impairment, questionable AD, and mild AD. Difficulties were also encountered converting the dissimilar scales used in these studies to an equivalent CDR. Given these difficulties, recommendations are made using the criteria for strength of evidence (appendix 2).
The published evidence on driving performance in those with AD supports the following recommendations. Decisions regarding license restrictions for drivers with AD must always be made in compliance with appropriate state laws and in consultation with the individual patient.
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Future research. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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The cost to society of driving by individuals with mild dementia needs to be determined. Whether periodic testing of cognitive decline in older individuals can reduce such costs is another question for future research.
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Disclaimer. |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Appendix 1: classes of evidence |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Class II: a) a retrospective study of a well-defined cohort which otherwise meets criteria for class 1a, 1b, and 1d; b) a prospective or retrospective study which lacks any of the following: adequate sample size, a well defined control group, adequate methodology, blinding of evaluators, a description of the inclusion or exclusion criteria, and information such as age, sex, and commonly used staging of dementia severity.
Class III: May have either a, b, or c: a) criteria of a class II article published in a nonpeer reviewed format; b) a small cohort or case report; c) evidence from expert opinion or consensus.
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Appendix 2: levels of recommendations |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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Guideline: A recommendation for patient management that reflects moderate clinical certainty (usually this requires class II evidence or a strong consensus of class III evidence).
Practice option: A strategy for patient management for which the clinical utility is uncertain (inconclusive or conflicting evidence or opinion).
Practice advisory: A practice recommendation for emerging or newly approved therapies or technologies based on evidence from at least one class I study. The evidence may demonstrate only a modest statistical effect or limited (partial) clinical response, or significant cost-benefit questions may exist. Substantial (or potential) disagreement among practitioners or between payers and practitioners may exist.
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Acknowledgments |
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Footnotes |
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References |
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Top.Article AbstractIntroductionBackground.Justification.Description of the process.Scientific reports.Statement of the evidence.Future research.Disclaimer.Appendix 1: classes of...Appendix 2: levels of...References |
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