An investigation of plasma interleukin-6 in sport-related concussion

BACKGROUND: Increasing evidence suggests inflammation is an important component of concussion pathophysiology. However, its etiology, restitution, and potential clinical repercussions remain unknown. The purpose of the current study was to compare the blood concentrations of interleukin (IL) -6, a prominent inflammatory cytokine, between healthy athletes and athletes with a sport-related concussion (SRC), while addressing the potential confounds of sex, recent physical activity, and the interacting effect of concussion history. METHOD: A prospective, observational cohort study was conducted on athletes at a single academic institute participating across 13 interuniversity sports. Follow-up of 96 athletes who agreed to provide a blood sample was completed: 41 athletes with a physician diagnosed SRC, and 55 healthy athletes. Ella(™), the high sensitivity immunoassay system by ProteinSimple was used to measure peripheral plasma concentrations of IL-6 within the first week (median = 4 days, range = 2–7) following injury. A resampled ordinary least squares regression was used to evaluate the relationship between IL-6 concentrations and concussion status, while partial least squares regression was used to evaluate the relationship between IL-6 and both symptom burden and time to clinical recovery. RESULTS: Regression analysis identified a negative relationship between plasma IL-6 concentrations and the interaction between an acute SRC and a history of concussion (β = -0.29, p = 0.029). IL-6 did not differ between healthy athletes and those with an acute SRC independent of concussion history, and was not correlated with either recovery time or symptom burden in athletes with SRC. CONCLUSION: Perturbations to circulating IL-6 concentrations, a key inflammatory cytokine, may be more pronounced following SRC in athletes who have a history of concussion. These results add to a growing body of evidence supporting the involvement of inflammation at all phases of recovery following SRC, and potentially support a concomitant effect of prior concussion on acute SRC pathophysiology.