A previous concussion has been linked to an increased risk of a subsequent car crash ending in permanent disability, not necessarily because of injury severity, but because the brain appears to lack the ability to fully recover.
In a population study of more than 900,000 adults treated after motor vehicle crashes, those with a documented history of concussion were about 15% more likely to be diagnosed with long-term disability than patients with no prior concussion. This increased risk persisted despite comparable crash or injury severity, hospital admission, and short-term healthcare costs, researchers reported.
“These results highlight the importance of traffic safety in general as well as preventing concussions in the first place,” Donald Redelmeier, MD, Centre for Injury Prevention, Sunnybrook Health Sciences Centre, Toronto, Canada, told Medscape Medical News.
“Clinicians need to consider that recovery after a concussion is sometimes incomplete with a loss of resilience that limits a person’s ability to recover from a traffic crash occurring years later,” Redelmeier added.
The study was published online January 21 in JAMA Network Open.
Compromised Neurocognitive Reserve?
Although previous research has shown that concussion history increases the risk of a motor vehicle crash, it has been unclear whether prior concussions also diminish neurocognitive reserve and hinder recovery from later injuries.
To investigate, Redelmeier and colleagues identified 907,984 adults (mean age 37 years, 52% male) with no preexisting disability who were injured in a motor vehicle crash between April 2003 and March 2023. Of these, 19,851 had a documented history of prior concussion and 888,133 did not.
Patients with a prior concussion tended to be younger, more likely to have a history of alcohol misuse, and more likely to have a mental health diagnosis such as anxiety. Acute injury severity scores following the crash were similar for patients with and without prior concussion.
During a mean follow-up of 10.5 years, 54,678 individuals were subsequently diagnosed with long-term disability. Patients with a prior concussion had a higher absolute rate of disability compared to peers with no concussion history (8.2 vs 5.7 per 1000 person-years).
In unadjusted analyses, this represented a 34% relative increased risk of long-term disability in those with prior concussion. In adjusted analyses, prior concussion remained independently associated with a 15% higher risk of long-term disability (P < .001).
“The overall effect size associated with a prior concussion was substantial, comparable with a diagnosis of sleep apnea, and greater than a diagnosis of heart disease,” Redelmeier and colleagues noted in their paper.
“The increased risk of long-term disability with prior concussion was independent of other measured risk factors, applied to diverse patient groups, and included those involved as passengers or pedestrians,” they added.
By way of limitations, the authors cautioned that each concussion is different, making an exact prognosis hard to estimate due to lingering uncertainties. Also, the observational study design precludes causal inference, and unmeasured factors such as childhood concussions, rehabilitation, and social determinants of health could influence outcomes.
Nonetheless, the results support past research on long-term prognosis after a motor vehicle crash. For example, an Australian analysis of more than 2000 adults injured in traffic accidents found that 23% were unable to resume full work duties after 6 months.
In addition, a US study of 590 adults injured in a crash identified ongoing deficits due to pain, anxiety, mobility, and restricted activity more than 1 year later, and a prospective cohort study of 64,000 individuals injured in car crashes in Sweden showed 8% had a permanent medical impairment when assessed after 2 years.
Concussion Not Fully Reversible?
In an accompanying editorial, Ramon Diaz-Arrastia, MD, PhD, Department of Neurology and Traumatic Brain Injury Clinical Research Initiative, University of Pennsylvania, Philadelphia, said this study supports the view that concussion, commonly thought of as a fully reversible transient neurologic disorder, is in fact a traumatic brain injury (TBI).
The take-home message for physicians, he noted, is that although most patients recover functionally from a concussion, usually within a few days to weeks, “concussions are not trivial injuries and are best conceptualized as TBIs.”
More broadly, he noted that some experts in the field have argued that the term concussion should be “retired as it has no clear and consistently understood definition and is a concept in a collision course with advances in neuroscience.”
“The problem,” said Diaz-Arrastia, “is that it is not yet clear what should replace it, as mild TBI is no better, as it is also imprecisely defined, confusing, and misleading.”
Redelmeier agreed that concussion and TBI are “sufficiently similar that a single term is sufficient.” But he prefers the term concussion. “It’s more familiar and avoids acronyms,” he said.
The study had no commercial funding. Redelmeier and Diaz-Arrastia had no disclosures.
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