There is increasing concern that individuals who sustain multiple concussions are at risk for prolonged or permanent neurologic damage, including early onset dementia. In a study of 30 Olympic boxers, chemical signs of ongoing brain injury were detectable two weeks after their last fight.1 Chronic traumatic encephalopathy (CTE), a form of dementia, may result from multiple concussions, either those sustained in the military from multiple blast injuries, or from contact sports such as boxing and football.2 CTE appears as a progressive decline of memory and cognition, as well as depression, suicidal behavior, poor impulse control, aggressiveness and, eventually, dementia. In addition, long term and possibly permanent damage to the pathways, or wiring, of the brain can be caused by concussion.3
High school athletes who sustain multiple concussions take longer to recover, are kept out of play longer, and report loss of consciousness more frequently (7.7 percent versus 4.4 percent) than athletes sustaining new concussions.4 A National Collegiate Athletic Association (NCAA) football study found that those players who had a history of multiple concussions were more likely to sustain another concussion.5 The study also found that a prior history of concussion may be associated with slower recovery. After a concussion, players most commonly complained of headache, dizziness/balance difficulties and feeling cognitively “slowed down.”
Thus, there is a substantial body of evidence that suggests worsened brain injury, and worsened neurologic outcomes, associated with multiple concussions. What is less clear, however, is how many is too many, and when someone who has had multiple concussions should be cleared to return to play or duty. For service members who have sustained multiple concussions, the military requires them to go through an extensive neurological evaluation.
1 Neselius S et al. CSF-Biomarkers in Olympic Boxing: Diagnosis and Effects of Repetitive Head Trauma. PLoS One. 2012;7(3):e33606. Epub 2012 Apr 4.
2 Stern RA et al. Long-term consequences of repetitive brain trauma: chronic traumatic encephalopathy. PM R. 2011; 3(10 Suppl 2):S460-7
3 Acute and Chronic Changes in Diffusivity Measures after Sports Concussion. Henry LC et al. Neurotrauma. 2011 Oct 4; Thalamus and Cognitive Impairment in Mild Traumatic Brain Injury: A Diffusional Kurtosis Imaging Study. Grossman EJ et al. J Neurotrauma. 2011 Sep 15
4 Castile L, Collins CL, McIlvain NM, Comstock RD. The epidemiology of new versus recurrent sports concussions among high school athletes, 2005-2010. Br J Sports Med. 2011.
5 Guskiewicz KM, McCrea M, Marshall SW, Cantu RC, Randolph C, Barr W, Onate JA, Kelly JP. Cumulative Effects Associated With Recurrent Concussion in Collegiate Football Players: The NCAA concussion study. JAMA 290: 2549-2555, 2003.