Older drivers with cognitive impairments : issues of detection and assessment

Abstract

Older drivers are often presented as a traffic safety problem. Age-related medical conditions such as dementias and stroke impair cognitive functions that are crucial for safe driving. Uncertainty remains regarding the most appropriate clinical methods to assess driving fitness in these patient groups. Furthermore, preclinical dementia and cognitive impairment may affect driving performance and lead to an increased crash risk. The first general aim of the thesis was to investigate the presence of cognitive impairment (CI) in crash-involved persons from the general older driving population. The second was to study different methods to evaluate the fitness to drive in clinical groups of older adults.

In study I a group of fatally crashed older drivers was investigated regarding neuropathology and informant-reported functioning. There were moderate to frequent densities of neuritic plaques (NPs), the hallmark of Alzheimer's disease, was in 25%. Such densities indicate the presence of Alzheimer's disease in persons 65 to 75 years. There were also hippocampal neurofibrillary tangles (NFTs) in 84%. There was no relationship between responsibility for the crash and the presence of NPs. Informant-reported deterioration was associated with age, but not with NPs or NTFs. The results suggest that the persons with neuropathological signs of Alzheimer's disease may have been asymptomatic, or that the informants were not observant of subtle decline associated with pathological processes.

Participants in study II were older drivers with temporarily suspended licenses due to unsafe driving. There were two subgroups: a) drivers involved in crashes and b) those with moving traffic violations. Compared to a control group with no recent crashes, subgroup a) had a lower level of performance on tests of visuoconstructive ability, psychomotor speed, and verbal and visuospatial episodic memory. There were no differences in performance between subgroup b) and controls. Results support the assumption of a causal relationship between CI and crashes in older drivers.

Study III was a three-year follow-up investigation of study II. Mortality tended to be higher in the case group, as compared to controls, and the presence of dementia or CI differed between groups. Subgroup a) from study II performed worse on all neuropsychological tests than did both previously non-crash involved controls and subgroup b). There was also more deterioration over time in group a). Results suggest that many older drivers with unsafe traffic behavior may have a preclinical dementing disease or another serious medical condition.

Study IV concerns stroke patients. The usefulness of a screening battery, the SDSA, to determine driving fitness, was evaluated. The SDSA was validated against driving test performance in 97 patients and attained 78% of correct classifications. Incorrect classifications appeared to be due to factors such as level of premorbid driving skill. Study V deals with driving tests among older patients with CI. The outcome (pass/fail) of the tests was compared for two groups: 1) patients driving their own cars and 2) patients driving dual-control cars. There were 16% more fails in group 2), but no overall difference on cognitive test scores between groups. Older patients with CI are probably more likely to fail the driving test when using dual-command cars because the need to adapt to an unfamiliar vehicle demands attentional resources that are needed to manage other aspects of the test.

Older drivers with demonstrated unsafe traffic behavior should be cognitively assessed. This should also be the case for older license holders with medical conditions susceptible to cause CI. However, in a policy perspective, it is necessary to carefully weigh the individual and societal consequences of license revocation against the crash risk of older drivers with CI.