Concussion research: a public health priority

Concussions are caused by a physical blow or jolt to the head resulting in either forces applied directly to the head (eg, a pitcher being struck by a batted ball) or movement of the brain within the skull (eg, anterioreposterior deceleration or rotational forces experienced in motor vehicle crash). Such forces disrupt normal cellular processes in the brain. Concussions are seen in all age, gender and ethnic groups but, because they are commonly sustained during sports and recreational activities, they have frequently been described in children. The estimated incidence of sports-related concussions in the USA ranges from 300000 to 3.8 million annually. 2 Estimating incidence is difficult because sports-related concussions frequently go undetected due to a lack of recognition of symptoms or intentional underreporting of symptoms. 34 Symptoms include physical complaints (eg, headache, fatigue, dizziness, noise intolerance), behavioural changes (eg, mood swings, depression, anxiety, irritability) and cognitive impairment (eg, inability to concentrate, decreased memory). While initial symptoms typically resolve in several days to occasionally several months after the injury, 5e8 in 10e15% these symptoms can persist much longer. Because of the heterogeneity of these injuries and their recovery, as well as the recognition that the length of time until symptoms resolve is more important clinically than the type of symptoms, grading scales and classification schemes have been abandoned. Of primary concern is determining when it is safe for the concussed patient to return to normal activities. Such activities mayincludemorephysicallystrenuousgameplayforathletes,but also simply the cognitive exercise of classwork for students or work for adults. Currently accepted guidelines indicate that return should not occur until the concussed patient can accomplish a stepwise progression of increased activity while remaining symptom free. 9 The risks of premature return to activities has