Adolescent athletes with a history of multiple concussions perform just as well on brief computerized tests of neurocognitive function than those without such history, although those who a history of two or more concussions self-reported more concussion symptoms, says a new study.
Analyzing data on a group of 643 elite 13- to 17-year-old elite Canadian hockey players, researchers at the University of Calgary found no significant correlation between the number of concussions and neurocognitive functioning, and no difference in the number or severity of symptoms between athletes who reported sustaining one prior concussion and those who had not sustained a concussion.
They did find, however, that those who had sustained two or more prior concussions self-reported a higher number of individual symptoms of concussion (5.3) and total symptom scores (10.9) than those in the no concussion group (2.8 and 4.9 respectively), and one concussion group (3.3 and 5.8 respectively).
Evidence of lingering effect inconclusive
The finding that multiple concussions had no lingering effect on neurocognitive functioning is consistent with some studies reporting no effect of multiple concussions on neurocognitive function, at least when employing a rapid computerized screen of neurocognitive abilities. Other studies, however, have found that athletes with a reported history of concussions performed significantly worse on tests of memory, visual processing and reaction time using the ImPACT computerized neurocognitive test battery than those who reported no prior concussion,  and that teenage athletes may be more vulnerable to the lingering effect of concussion on short-term memory than younger athletes and adults.
The Canadian study is consistent with an earlier study  which found that high school athletes with a history of concussions, even six months or more after their last concussion, report more concussion-related symptoms (e.g. headache, balance problems, dizziness, fatigue, trouble falling asleep, sleeping less than usual, irritability, nervousness, numbness or tingling, feeling slowed down, difficulty concentrating, difficulty remembering, and visual problems) than peers with no concussion history or who have only suffered one.
The researchers cautioned, however, against concluding that the previous concussions are truly causal of the higher levels of symptom reporting. "Elevated symptom reporting may not be the direct result of the past concussions," wrote lead author Brian Brooks, MD, of the University of Calgary and Alberta Children's Hospital, who said "further research into the cumulative effects of concussion on developing brains is needed."
Nevertheless, Brooks said, "Higher levels of symptoms in those with previous injuries are important to consider when assessing the potential acute effects of a recent concussion and monitoring recovery in an adolescent, as well as when considering the increased risk of sustaining another concussion."
The authors noted several limitations to their study, including reporting bias, results that might not translate from the elite level hockey players studied to athletes in other sports or to non-athletes, the cross-sectional nature of the study (a longitudinal study in which athletes are followed over several years to document injuries and repeat testing, might have allowed researchers to ascertain if the differences between the 2+ concussion group and the 0 and 1 concussion group were truly the result of prior concussions or any other factors), and the fact that it employed a rapid computerized screen of neurocognitive abilities, not other methods of measuring neurocognitive functioning, such as more comprehensive paper and pencil testing or tests of executive functionwhich have demonstrated lingering effects of concussion in adolescents.
Nor did the study include other methods of examination with the potential to identify lingering neurological effects from prior multiple concussions, such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging(DTI)[7,8] to detect subtle changes in brain function.
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