The dangers of multiple concussions have been highlighted in a US study. © Mike Bain
The new study found increased rates of concussion-related symptoms in high-school athletes with a history of two or more previous concussions.
The findings will appear in an upcoming issue of Neurosurgery, official journal of the Congress of Neurological Surgeons.
The study, led by Dr Philip Schatz, of Saint Joseph's University, Philadelphia, the International Brain Research Foundation in New Jersey, and the Sports Concussion Center, also in New Jersey, suggests some teen athletes with multiple concussions may already have early signs of post-concussion syndrome.
"It appears that youth athletes who sustain multiple concussions experience a variety of subtle effects, which may be possible precursors to the future onset of concussion-related difficulties," the researchers wrote.
The study was based on more than 2500 high school athletes in three states.
As part of routine pre-season evaluations, all students were evaluated using a standard questionnaire regarding concussion-related symptoms.
Rates of different types of symptoms were assessed for 260 athletes reporting one previous concussion and 105 athletes with two or more previous concussions, compared to a random sample of 251 athletes with no previous concussions.
None of the athletes had sustained a concussion within the past four months.
The results showed higher rates of concussion-related symptoms in athletes with previous concussions, especially those with two or more concussions.
After adjustment for other factors, athletes with two or more concussions had higher ratings for three symptom "clusters":
o Cognitive (intellectual) symptoms, such as feeling "mentally foggy" or having trouble remembering things.
o Physical symptoms, such as headache, balance problems, or dizziness.
o Sleep symptoms, such as sleeping more or less than usual.
These symptoms were not significantly different for athletes with one versus no concussions. There were no differences in emotional symptoms, such as irritability or sadness.
Recent reports have highlighted the cognitive and psychological after-effects of repeated concussions, including cases of chronic traumatic encephalopathy and degenerative brain disease in retired football players and other athletes.
"As a result of these findings, there is concern that repeated concussions can result in brain pathology that leads not only to cognitive difficulties, but to serious emotional sequelae in later life," the researchers wrote.
The results show "subtle, yet significant increases" in concussion-related symptoms among high school athletes with two or more concussions.
However, Schatz and his colleagues emphasised that their findings do not reflect any direct causal relationship - for example, it may be that athletes with multiple concussions are "simply more sensitive to physical, cognitive, and emotional fluctuations".
While further research is ongoing, they believe their findings should "serve as a caution for parents, coaches, and sports medicine personnel supervising high school and other youth athletes with a history of concussion."