History of undiagnosed concussion is associated with concussion-like symptoms following subconcussive head impacts

Objective Immediate removal from activity after sport-related concussion is associated with less time missed from sport, a shorter symptomatic period, and better outcomes on acute clinical measures than delayed removal from activity. However, the effects of undiagnosed concussion on clinical outcomes have not been studied. In the case of an undiagnosed concussion, when the athlete is not removed from play, he/she may undergo subsequent repetitive head impacts. Subsequent head impacts may prevent complete recovery and make the athlete more sensitive to even mild mechanical head impact. The purpose of this study was to determine if soccer players with a history of undiagnosed concussion are more likely to report concussion-like symptoms following typical soccer heading than those without a history of undiagnosed concussion. Methods Thirty-one adult amateur soccer players (17 males and 14 females, 22.3 ± 4.5 years, 171.0 ± 9.2 cm, 71.9 ± 11.4 kg) completed a self-reported concussion/sport history questionnaire as part of a larger study aimed to identify behavioral and biomarkers of subconcussion. Participants were asked to report diagnosed and undiagnosed concussions. Undiagnosed concussions consisted of unreported and unrecognized concussions. Participants also indicated concussion-like symptoms typically experienced after soccer heading. A χ2 analysis was used to determine if a history of undiagnosed concussion was associated with prolonged concussion-like symptoms following subconcussive head impacts. Results Individuals with a history of undiagnosed concussion were more likely to report concussion-like symptoms following soccer heading (χ2 = 5.114, p = 0.024; Likelihood Ratio = 4.693, p = 0.030). Conclusions The results of this study suggest that individuals who experience unreported or unrecognized concussions may be more likely to experience concussion-like symptoms following repetitive subconcussive head impacts and highlight the importance for athletes in immediately reporting concussion signs and symptoms. We speculate that these individuals may not fully recover and may remain sensitive to mild mechanical head impact even years following their concussion.