DURATION OF COGNITIVE DYSFUNCTION AFTER CONCUSSION, AND COGNITIVE DYSFUNCTION AS A RISK FACTOR - A POPULATION STUDY OF YOUNG MEN

Objectives: To establish how long cognitive dysfunction lasts after co ncussion, and the extent to which it may be a predisposing risk factor for concussion, by examining the prevalence of cognitive dysfunction among young men who have sustained concussion. Design: Observational s tudy. Setting: Denmark. Subjects: 1220 young men who had been admitted to hospital for concussion between the ages of 16 and 24 (identified in a national register of admissions) and who had also been cognitivel y tested by the Danish conscription draft board.Main outcome measure: Score on the draft board's cognitive screening test, dichotomised as d ysfunctional or non-dysfunctional (20.4% of the general population of Danish men appearing before the draft board had a dysfunctional score) . Results: 700 of the 1220 men had been tested after sustaining concus sion; 520 had been tested before concussion. Four (50%) of the eight m en who were tested less than seven days after the injury had a dysfunc tional score. Among groups of the remaining 692 men who were tested at later time points after injury, the rates were only marginally raised (range 21.4% to 26.5%) above the population level. Among men tested b efore injury, the rate of dysfunctional scores was higher (30.4% (158/ 520)). Apart from suggesting cognitive dysfunction as a risk factor fo r concussion, this higher proportion seems to relate to the fact that they were typically injured as young adults, whereas those men who wer e tested after concussion had more often been injured as adolescents. The relative risk for concussion in the presence of cognitive dysfunct ion is estimated to be 1.57 (95% confidence interval 1.32 to 1.86). Co nclusions: Cognitive dysfunction is not only a short term consequence of concussion but also a predisposing risk factor for concussion, more so for young adults than for adolescents.