State Driver’s License Laws Could Lead to Underdiagnosis of Dementia, According to New Research

It’s uncomfortable to talk about older adults and driving, a fact that many families who’ve worried about a loved one’s dwindling eyesight, reaction time, or cognition behind the wheel are well aware of. The ability to drive isn’t a right, but in many parts of the U.S. it’s become a necessity, the only way to access the world outside the home. When an older adult’s freedom threatens their safety, who gets to make the choice to take a car or license away?

For a long time, the answer has been an unsure combination of the U.S. government, physicians, and family members. But as the population of Americans older than 65 grows at a faster rate than any other age bracket, seniors’ presence on the road is growing as well. According to the Federal Highway Administration (FHA), there were 48 million licensed drivers ages 65 and older in 2020, nearly 70% more than there were two decades before. Data from the FHA show that seniors account for 20% of drivers on U.S. roads, where the types of impairments frequently associated with aging incur a greater risk of crash involvement. 

Policies meant to ensure drivers remain capable as they age—such as stricter vision-testing for license renewals and reporting requirements for dementia diagnoses—exist, but according to new research presented in late October at the 2023 Clinical Trials on Alzheimer's Disease conference, they may be undermining—or at least complicating—their intended outcomes. For example, some states require that drivers (or their doctors) notify the Department of Motor Vehicles if they get diagnosed with certain conditions that are impossible to evaluate at DMV facilities, like diabetes, seizure disorders, and most importantly, dementia.

Dementia not only directly affects driving abilities, but it also reduces a person's capacity to recognize their own impairments or dangerous behaviors. Concerned by this dual hazard especially among rising rates of dementia diagnoses, a team led by Hankyung Kate Jun, a research fellow at Harvard Medical School’s Department of Healthcare Policy, wanted to understand how dementia-reporting policies were impacting public health and driver safety. They found only one study ever published on the topic, which looked at dementia diagnoses among those hospitalized after crashes, and found no real trend in line with the policies. So, the team decided to compare expected and actual dementia diagnoses in each state using a predictive model—and found that physicians in the four states that require doctors to notify the DMV when they’ve diagnosed a patient were significantly more likely to underdiagnose dementia. In California, Oregon, Delaware, and Pennsylvania, the rate of underdiagnosis was 14%, compared to 9% in other states.

Fourteen other states require patients themselves to notify the DMV of their own diagnoses, but Jun’s team found no difference in diagnosis margins between these states and states with no mandate whatsoever. The researchers plan to next look at the number of reports actually made to each state’s DMV, licensing changes they’ve caused, and road-accident data—if they can get that information, they can potentially figure out if these unenforced self-reporting mandates are at all effective.

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Jun believes that the fear of losing the ability to drive may be stopping people from telling the DMV of dementia diagnoses. And in the four states with physician-reporting mandates, she adds, that fear could be discouraging people to seek medical help in the first place. “I do believe like the reason why doctors underdiagnose is not because the doctors want to underdiagnose, but because the patients are reluctant,” she says.

Though the study doesn’t reveal whether these policies are effective in preventing crashes and injuries, it does suggest that they may be part of the family and individual calculus determining whether older people developing dementia are getting the care they need—and highlights the difficult balance between ethical and safety concerns that state DMVs are tasked with establishing in an aging country.