Driving Fitness in Different Forms of Dementia: An Update

Max Toepper, PhD; Michael Falkenstein, MD

Disclosures

J Am Geriatr Soc. 2019;67(10):2186-2192. 

In This Article

Discussion

The results of the current literature review suggest that people with severe or moderate dementia are no longer fit to drive, irrespective of the type of dementia.[23,24] People with MCI or mild dementia may still be able to drive under certain circumstances, dependent on the characteristics of the underlying dementia syndrome. In fact, reduced driving fitness is particularly related with impaired attention and executive functioning (ie, reduced psychomotor speed and cognitive flexibility)[55,56] as well as with visual and spatial deficits.[55,57] Consequently, dementia syndromes with pronounced deficits within these domains (ie, non-Alzheimer syndromes) may impair driving fitness more and earlier than dementia syndromes with mainly memory dysfunctions (ie, ADD). Importantly, all forms of dementia have in common that the ability to drive is impaired at some point in the course of the disease.

Alzheimer Disease Dementia

In ADD, driving abilities can be already impaired in early disease stages. Meta-analytical evidence indicates that a third of the patients with mild ADD fail an on-road test, compared to 1.6% of healthy drivers.[27] Drivers with mild ADD commit various driving errors and endanger road safety with their maneuvers.[29] However, this may not necessarily apply to the prodromal stage of the disease. The prodromal stage of ADD is defined as aMCI, which is typically characterized by an isolated episodic memory dysfunction.[12] Since episodic memory does not belong to the core requirements for driving fitness,[58] driving in aMCI might be still most likely possible, albeit not completely safe.[27]

Non-alzheimer Dementias

In non-Alzheimer dementias, such as VaD, FTD, DLB, and PDD, driving studies are sparse. However, about half of these patients do not pass a practical driving test in early disease stages, compared to 11% in healthy controls.[37,39] In the non-Alzheimer syndromes, deficits in driving-relevant cognitive functions are frequent, whereas memory deficits may be less pronounced.[44,59,60] Importantly, this already applies to the prodromal stage of these syndromes, which is referred to as non-amnestic MCI.[12] Non-amnestic MCI is usually characterized by cognitive deficits in non-amnestic cognitive domains, such as language, attention, executive functioning, or visuospatial skills, most of which are closely related to different driving outcomes in older adults.[56] Hence, drivers with non-amnestic MCI may already show increased driving difficulties that exceed the difficulties of drivers with prodromal ADD (aMCI).

Vascular dementia. The few studies on driving fitness in VaD suggest pronounced driving impairments in these drivers. However, whether patients with VaD are still able to drive seems to depend on the kind of VaD and the profile of vascular damage. Early multi-infarct dementia, for example, may be characterized by plateaus with rather mild cognitive symptoms. During this period, driving might still be possible until the next strokes occur.[39] Subcortical VaD, by contrast, is associated with a more constant progressive decline due to increasing gray matter atrophy and decreasing white matter integrity.[61] At the time of diagnosis, many of these patients already show distinct cognitive slowing and executive dysfunctions,[59] both of which most likely impair driving fitness. Overall, on-road performance was reported to be significantly decreased in VaD patients: about 70% fail an on-road test in early disease stages,[37,39] compared to 11% of healthy drivers. Severe driving difficulties are also reported for patients having experienced a single stroke.[42]

Frontotemporal dementia. Patients with FTD exhibit pronounced driving impairments due to executive dysfunctions and driving-related behavioral symptoms. Thereby, ignorance and risk tolerance appear to be the most dangerous risk factors for driving safety in this patient group. They lead to an aggressive and risky driving style involving frequent traffic violations.[45] Compared to drivers with ADD (19%), double as many FTD patients caused at least one accident since onset of the disease (37%);[32] between 50% and 60% of drivers with very mild and mild FTD fail an on-road test, compared to 11% in healthy drivers.[37,39] Hence, it was suggested that patients with FTD should stop driving as soon as possible.[48] Importantly, this may not necessarily apply to all FTD subtypes. The semantic and the nonfluent PPA variants of FTD show less pronounced behavioral symptoms but primarily involve semantic memory and verbal dysfunctions. Since those functions are less relevant for driving performance, driving may remain safe and fluent for a longer time than in FTD patients with the behavioral variant. On the other hand, drivers with the semantic PPA subtype may have more difficulties in traffic sign comprehension that even exceed the difficulties of drivers with ADD.[49] Since most studies combined different FTD subtypes, however, a differentiation between FTD variants appears not to be possible at present.

Dementia with Lewy bodies. DLB also appears to be associated with impaired driving abilities.[50] Licensed drivers with DLB typically show cognitive deficits in attention, executive functioning, and visual perception[60,62] that are even more severe than in ADD.[63] Moreover, DLB is associated with a fluctuation of attention, hallucinations, and extrapyramidal symptoms.[60,62] Both cognitive and noncognitive risk factors may severely impair driving skills in DLB; between 35% and 40% of these patients fail an on-road driving assessment in early disease stages, compared to 11% of healthy controls.[37,39]

Parkinson disease dementia. In PDD, cognitive symptoms particularly include deficits in attention, executive functions, and visuospatial abilities,[60] all of which appear to be closely connected to impaired driving fitness.[56] Similar to DLB, there are a number of noncognitive risk factors for driving safety as well, such as fatigue or extrapyramidal symptoms.[60] Together, these risk factors may severely impair driving performance in PDD; only 18% pass an on-road driving assessment.[54] The conclusions for PDD may be pretty much the same as for DLB due to great similarities between these syndromes.

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