Delayed Driving Reactions Even After Concussion Symptoms Resolve

August 03, 2020

Individuals who have experienced a concussion may not be ready to drive even after symptoms have resolved, new research from a small study suggests. 

A small study of college students showed that those with recently-resolved symptoms from concussion showed slower driving reaction times on three different tests compared with their peers who did not experience a concussion.

"Amazingly, there is little focus on driving after a concussion," senior investigator Julianne D. Schmidt, PhD, University of Georgia, Athens, told Medscape Medical News

"There is no mention of driving in current concussion guidelines and in a survey we conducted, driving was mentioned only about 50% of the time in acute concussion cases. Our results show we should be thinking about this more," she said.

Schmidt noted that there have been a few previous studies suggesting that impaired reaction times can occur in acute concussion. However "our study suggests reaction times relevant to driving may still be somewhat impaired after other symptoms of concussion have subsided,” she added.

The findings were presented last Friday and Saturday at the American Academy of Neurology's Sports Concussion Virtual Conference.

Red Light, Green Light

The study compared reaction times in 14 college students with recently resolved symptoms from concussion (average, 2-3 days post-symptoms and 16 days after the injury) with 14 students without concussion who acted as the control group. The two groups were matched for age, sex, and driving experience.

All participants underwent simulated driving reaction time tests and computerized neurocognitive tests commonly conducted in concussion evaluations. 

The simulated driving tests included stopping at a red light, a child running in front of car, and the time to move out of the way of a vehicle rapidly approaching from behind.

Although there was a large magnitude of difference in all three tests between the concussion group and the control group, the difference did not reach statistical significance, lead author Landon Lempke, MEd, also from the University of Georgia, told Medscape Medical News

He noted that was "probably because of the small sample size in the study."

The stoplight test showed that concussed individuals responded 0.24 seconds later than controls, which was the equivalent of 15.6 feet in stopping distance. 

Similarly, during the simulation with a child running in front of a car, the post-concussion individuals took 0.06 seconds longer to react, which is the equivalent of 3.3 feet. 

"The composite of all three driving reaction time tests showed that the concussion group reacted one third of a second slower than the control group. This translates into an extra 22 ft before the driver would even start to think about stopping," Lempke said. 

"That could be the difference between having an accident or not," he added.

"Gold Standard" Test Needed

In the more conventional complex computerized neurocognitive tests commonly conducted in patients with concussion in clinical practice, the concussion group was slower by 60 milliseconds in the reaction time tests, a result that was statistically significant.

The researchers also looked at whether the driving reaction times were related to the conventional neurocognitive tests and found that this was not generally the case.   

"Only two outcomes from a multitude of tests correlated between the two scenarios," Lempke noted. "This suggests that the tests we normally conduct in clinical practice don't tell us much about whether a patient is ready to drive again and are not really a valid tool for driving."

"In a perfect world we would have a gold standard concussion test that would also apply to driving, but in our study this was not the case," Schmidt said.

She added that "this is just preliminary evidence" and more driving-specific outcomes embedded in concussion evaluations are needed in the future.

Although the driving tests used in the study are not difficult to perform, they  involve expensive equipment that limits their reach, Schmidt noted.

"We need a simple and cheap test that can be applied to driving. There are a few out there that are used in other neurological disorders, such as stroke and Parkinson's, to determine if patients are ready to return to driving. We need to study these tests in concussion patients and see whether they could be added to the battery of tests already used," she added.

Lempke cautioned that this was a small study so the results should be considered exploratory and need to be confirmed in larger studies.

"There is surprisingly little research on this topic, so it is hard to nail down recommendations," Schmidt added.

"We also have to be careful not to be overstringent with guidelines on driving, which may prevent people seeking care after a concussion. We need to try and strike a balance between safety on the road and ensuring patients access appropriate treatment after concussion," she said.

Small but Important

Commenting for Medscape Medical News, Brian Hainline, MD, chief medical officer of National Collegiate Athletic Association and codirector of the AAN Sports Concussion Conference, said that although it's an important study it is also a small pilot trial that has not yet been published in a peer-reviewed journal. 

"That being said, the implications of this study are important and should be validated with a larger, more robust prospective study," said Hainline, who was not involved with the research.

"Physicians often discuss return-to-activity but do not routinely discuss operating potentially dangerous machinery or driving an automobile/truck," he noted.

"This small study suggests that standardized neurocognitive tests may miss subtle delays in reaction time that could have real-time manifestations when driving an automobile, suggesting that clinical recovery in concussion does not mean full brain recovery,” Hainline said, adding that there are evolving, objective biomarker studies that also show a difference between clinical and neurophysiological recovery.

"Understanding real-life implications," he stressed, "will continue to be important going forward."

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