Traumatic brain injury (TBI) is a leading cause of injury and death in the United States. TBI is responsible for approximately three million emergency department visits and contributes to the death of about 50,000 people annually. Mild TBI, often referred to as concussion, is the most commonly occurring severity. While TBI may be thought of as an acute event, symptoms commonly linger following initial injury. These “post-concussive symptoms,” which often include headaches, fatigue, dizziness, irritability, loss of memory, are caused by a cascade of neurological events that occur in response to the damage that the injury has done to brain cells and, subsequently, the energy that is required to repair this damage. Often, these symptoms resolve within 7-10 days of injury. However, some people experience long-term symptoms following TBI, a condition termed Post-Concussive Syndrome (PCS). What determines whether a TBI might result in PCS? Researchers are trying to address this question, and they have already identified several factors that may play a role.
Much of the research performed on TBI focuses on two major groups: athletes and military service members. Research on student athletes has suggested that age may be a predictor of recovery, and, though research is mixed, there is evidence that adolescents and young adults may be the most vulnerable for development of PCS. One possible explanation for this association is that younger athletes may be less likely to take the necessary time for recovery due to greater pressures to return to play. However, some studies suggest that a difference in reporting between younger and older athletes may play a role: younger children may have a harder time understanding and verbalizing their symptoms, so the development of PCS in this age group may be underreported, while adolescents and young adults have an easier time explaining how they feel.
Much like age, there is conflicting evidence that sex differences can predict vulnerability to PCS. While some studies suggest no association, others suggest that women are more likely to experience post-concussive symptoms for a month or more than are their male counterparts. Some physical reasons, such as sex-related differences in neck strength, may contribute to this difference, but it is also speculated that women and men report symptoms at different rates.
Prior history of TBI and concussion symptoms
Some studies suggest that having a history of multiple TBIs increases the likelihood of developing PCS. In a large-scale study of male and female college athletes, researchers with the NCAA Injury Surveillance Program assessed the relationship between PCS and several factors, such as sex, history of concussion, the level of contact at the time of injury, and specific concussion-related symptoms. They saw an association with PCS and recurrent TBI, as well as a relationship between specific concussion symptoms such as retrograde amnesia, difficulty with concentration, insomnia, and sensitivity to light.
Mental health issues
Multiple studies have investigated the association with pre-injury mental health issues and the risk for PCS. The strongest association has been shown in patients with depression: those who report stronger depressive symptoms are more likely to develop PCS following injury. Interestingly, depression seems to be a risk factor for PCS both when it is present prior to injury and when it develops after the injury occurred.
Recently, one group of investigators reported that IQ may be a predictor of PCS. In a study in which researchers conducted neuropsychological evaluations on 31 military veterans six or more months after experiencing a TBI, they found that lower IQ scores (determined prior to injury) were associated with higher risk of PCS. Again, one explanation for this relationship is that a higher IQ is associated with a greater ability to conceptualize one’s symptoms more thoroughly and express them more clearly, which facilitates being granted more recovery time, which is particularly important in a military theater environment. Notably, the authors point out that this is not an association of education level but of cognitive ability.
Ultimately, the goal of this research is to improve patient outcomes. If we gain a better understanding at the time of injury the likelihood that PCS will develop, perhaps we can make more informed recommendations for treatment and recovery.
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Kontos, Anthony P., Jaime McAllister-Deitrick, and Alicia M. Sufrinko. "Predicting post-concussion symptom risk in the ED." Pediatric neurology briefs 30.3 (2016): 19.
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Stewart-Willis, Jada J., et al. "Premorbid IQ predicts postconcussive symptoms in OEF/OIF/OND veterans with mTBI." Archives of clinical neuropsychology 33.2 (2017): 206-215.
Zuckerman, Scott L., et al. "Predictors of postconcussion syndrome in collegiate student-athletes." Neurosurgical focus 40.4 (2016): E13.