Researchers analyzing over three million patients in Ontario discovered that even a single concussion can leave lasting driving impairments, raising crash risk far more than conditions like sleep apnea or epilepsy.
Study: Concussions and risk of a subsequent traffic crash: retrospective cohort analysis in Ontario, Canada. Image credit: Southworks/Shutterstock.com
Concussion, a form of mild traumatic brain injury, can significantly increase the risk of a subsequent motor vehicle crash, as reported by a new study published in BMJ Open.
Understanding concussion and driving
Motor vehicle crashes are a leading cause of morbidity and mortality worldwide. Certain medical conditions, such as epilepsy, sleep apnea, or substance use disorder, which cause cognitive and functional impairment, can potentially increase the risk of a motor vehicle crash.
Thoughtful counselling and medical care for people living with these conditions can potentially reduce traffic crashes and save lives. In some countries, policies mandate that clinicians provide safety warnings to patients who are not medically fit to drive due to functional deficits.
A concussion is a type of mild traumatic brain injury caused by a direct blow to the head. The condition is associated with temporary deficits in functioning after which the affected person recovers. Symptoms sometimes last for weeks, including headaches, insomnia, dizziness, amnesia, fatigue, confusion, irritability, depression, delayed reaction time, and difficulty concentrating.
Although most people recover without long-term effects, there remains uncertainty about whether recovery is complete and whether there are no ongoing impairments. Another adversity is that a concussion can predispose patients to another concussion with further neurological consequences.
Given the potential association of concussion with neurocognitive and functional deficits, the current study aimed to explore whether a past concussion increases the risk of a subsequent traffic crash.
A total of 3,037,028 patients were analyzed, including 425,158 with a concussion and 2,611,870 with an ankle sprain (active controls). The risk of motor vehicle crashes requiring emergency medical care was compared between patients with a concussion and an ankle sprain.
Concussions heighten crash risk
The study identified a total of 200,603 patients with a concussion or an ankle sprain who experienced a subsequent traffic crash during a follow-up period of 10 years. This estimate was equivalent to an absolute risk of 1 in 15 patients.
The risk of a traffic crash was 49% higher among patients with a concussion compared to those with an ankle sprain. The risk was especially high during the first month after a concussion, showing about a sixfold increase compared to controls.
Other factors that were significantly associated with an increased traffic crash risk after a concussion included younger age, male gender, a rural home location, lower socioeconomic status, late-night driving, and a diagnosis of alcohol misuse.
A separate analysis involving patients with more than one concussion revealed a 73% higher traffic crash risk after a single concussion; a 114% higher risk after two concussions; and a 124% higher risk after three concussions. However, such a robust dose-response association was not observed in patients with multiple ankle sprains.
Artificial intelligence (XGBoost) models were applied to adjust for potential confounding factors and confirmed that concussion patients still had about a 40% higher crash risk compared with controls, supporting the robustness of the association. “Negative control” analyses for unrelated medical emergencies such as conjunctivitis and kidney stones showed no excess risk. Further, they indicated that the observed link between concussion and crash risk was specific rather than general to all medical conditions.
Implications for safer driving
The study reveals that having a concussion significantly increases the risk of a subsequent motor vehicle crash, particularly during the early weeks after a concussion. The risk is more pronounced after two or more concussions.
Previous simulation studies suggest that concussion is associated with specific neurological disabilities that may result in reduced vehicle control, altered driving skills, or persistent driving impairments. A survey of adults has reported an association between mild traumatic brain injury and aberrant driving behaviors. These impairments may contribute to the risk of a traffic crash.
The magnitude of concussion-related traffic crash risk observed in the study is substantially higher than the previously estimated risks related to sleep apnea or uncontrolled epilepsy, justifying a safety warning from clinicians.
Overall, the current study findings suggest that current mitigation efforts are insufficient. Since driving has become an essential part of modern life, clinicians should advise patients with a concussion to be cautious about their increased risk of a traffic crash.
Post-concussion risks can also be reduced by effective care of symptoms, such as treating headaches, sleep disturbance, depression, and substance misuse. Other risk mitigation strategies include temporarily reducing traffic exposure by avoiding high-speed, long-distance road trips or late-night driving. Campaigns raising awareness about concussion-related traffic crashes may also protect the patient and the community.
Since the causality of observed associations could not be determined, there remains a possibility that factors that predispose patients to concussions may also predispose patients to a traffic crash. This possibility of reverse causality highlights that concussion is not necessarily the cause of a subsequent traffic crash, and that prioritizing concussion treatment may not necessarily improve road safety.
The presence of potential confounding factors makes it challenging to identify the mechanisms underlying the association between past concussion and future traffic crash risk. Furthermore, each concussion is unique in anatomy, energy, angularity, and severity. Therefore, average risks may not apply to individual patients.
Since a concussion is often associated with decreased attention, delayed reactions, transient confusion, mood disorders, cardiac arrhythmia, memory deficits, and sleep difficulties, future research is needed to assess neurocognitive deficits after a concussion.
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