Sports activities are a common cause of concussion, a form of mild traumatic brain injury. Symptoms include loss of consciousness, confusion, memory difficulties, and other signs of brain dysfunction. Diagnosis is clinical with neuroimaging done as needed. Neuroimaging is not mandatory because there is rarely any evidence of structural brain injury. Early return to competition can be harmful; once symptoms are resolved, athletes can gradually resume athletic activity.
Concussion is a transient disturbance in brain function caused by head injury, usually a blow. By definition, there are no structural brain abnormalities visible directly or on imaging studies, in contrast to more serious brain injuries (traumatic brain injuries [TBIs]).
Pathophysiology is still being clarified, but brain dysfunction is thought to involve excitotoxicity, which is neuronal damage caused by excessive release of excitatory neurotransmitters, particularly glutamate.
Estimates of the incidence of sports-related concussion in the United States vary from 200,000 a year up to 3.8 million a year (1); the highest numbers include rough estimates of injuries that are not evaluated in a hospital or otherwise reported. The awareness and thus reporting of concussions has risen significantly in the past decade—the incidence of serious and fatal sports-related TBI has not increased similarly. Sports that routinely involve high-speed collision (eg, football, rugby, ice hockey, lacrosse) have the highest rates of concussion, but no sport, including cheerleading, is free of risk. Although estimates vary, up to 20% of participants in contact sports have a concussive injury over the course of a season (2).
Repeat injury
Unlike with other causes of concussion (eg, vehicular accidents, falls), which are usually isolated events, sports participants are continually exposed to risk of concussion. Thus, repeat injury is common. Athletes are particularly vulnerable if the repeat injury occurs before they have fully recovered from a previous concussion, but even after recovery, athletes who have suffered one concussion are 2 to 4 times more likely to suffer another concussion at some point. Also, repeat concussions may occur after a less severe impact.
Furthermore, although most athletes eventually recover fully from a single concussion, up to 40% of those who had multiple (even apparently minor) concussions develop chronic traumatic encephalopathy (CTE, initially described in boxers and termed dementia pugilistica). In CTE, patients have structural neurodegenerative changes, including cortical atrophy (3), somewhat similar to changes present in patients with Alzheimer disease. Symptoms can include
Dementia-like symptoms (eg, disturbances in memory, cognition, mood, or behavior)
Impaired judgment and decision making
Personality changes (eg, irascibility, volatility)
Several prominent retired athletes who had sustained recurrent TBI have committed suicide.
One surveillance database reported approximately 2.2 deaths per year over a 10-year period attributed to traumatic brain injuries sustained by college and high school football players with many players having a previous concussion (4).
Second-impact syndrome
Second-impact syndrome is a rare but serious complication of concussion. In this syndrome, acute, often fatal brain swelling occurs when a second concussion is sustained before complete recovery from a previous concussion. Vascular congestion is thought to lead to rapidly increased intracranial pressure (ICP) that is difficult or impossible to control.
The mortality rate approaches 50% (5).
References
1. Hallock H, Mantwill M, Vajkoczy P, et al: Sport-related concussion: A cognitive perspective. Neurol Clin Pract 13(2):e200123, 2023. doi: 10.1212/CPJ.0000000000200123
2. Gessel LM, Fields SK, Collins CL, et al: Concussions among United States high school and collegiate athletes. J Athl Train 2007;42(4):495-503.
3. McKee AC, Mez J, Abdolmohammadi B, et al: Neuropathologic and clinical findings in young contact sport athletes exposed to repetitive head impacts. JAMA Neurol 80(10):1037-1050, 2023. doi: 10.1001/jamaneurol.2023.2907
4. Kucera KL, Yau RK, Register-Mihalik J, et al: Traumatic Brain and Spinal Cord Fatalities Among High School and College Football Players - United States, 2005-2014. MMWR Morb Mortal Wkly Rep 2017;65(52):1465-1469. Published 2017 Jan 6. doi:10.15585/mmwr.mm6552a2
5. Ling GS, Marshall SA: Management of traumatic brain injury in the intensive care unit. Neurol Clin 2008;26(2):409-viii. doi:10.1016/j.ncl.2008.02.001
Symptoms and Signs of Sports-Related Concussion
The most obvious disturbance of brain function with a concussion is
Loss of consciousness
However, many patients do not lose consciousness but instead manifest symptoms and signs such as
Confusion: Appears dazed or stunned, is unsure of opponent or score, answers slowly
Memory loss: Does not know plays or assignment, does not recall events before the injury (retrograde amnesia) or afterward (anterograde amnesia)
Vision disturbance: Has double vision or light sensitivity
Dizziness, clumsy movements, impaired balance
Headache
Nausea and vomiting
Tinnitus
Loss of smell or taste
Postconcussive symptoms are symptoms that may be present for a few days to weeks after concussion; they include
Chronic headaches
Short-term memory difficulties
Difficulty concentrating
Fatigue
Difficulty sleeping
Personality changes (eg, irritability, mood swings)
Sensitivity to light and noise
Postconcussive symptoms typically resolve in a few weeks to several months.
Pearls & Pitfalls
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Diagnosis of Sports-Related Concussion
Clinical evaluation
Sometimes neuroimaging to exclude more serious injuries
Athletes with possible concussion should be evaluated by a clinician with experience in evaluation and management of concussions. Sometimes such clinicians are on site at high-level athletic events; otherwise, sideline staff should have training in recognizing concussive symptoms and protocols for referring patients for evaluation.
Diagnostic tools, such as the Standardized Assessment of Concussion (SAC) or the Sports Concussion Assessment Tool, 5th edition (SCAT5), can help coaching staff, trainers, and inexperienced clinicians screen athletes on site. (For tools and training information for anyone who needs to recognize, respond to, and try to prevent concussion and other serious brain injuries, see CDC "Heads Up" programs.)
Neuroimaging is not helpful to diagnose concussion itself but is done if more serious brain injury (eg, hematoma, contusion) is suspected. Typically, CT should be done if patients have any of the following:
Loss of consciousness
Glasgow Coma Score (GCS) < 15 (see table Glasgow Coma Scale)
A focal neurologic deficit
Persistently altered mental status
Other signs of deterioration
Formal neurocognitive testing can likely show abnormalities in symptomatic patients but is not typically done unless postconcussive symptoms last longer than expected or the patient has severe cognitive problems. However, some athletic programs do baseline neurocognitive tests on all participants and repeat them after concussion so that more subtle abnormalities can be identified and further participation deferred until the person returns to baseline.
Treatment of Sports-Related Concussion
Removal from contest or activity
Rest
Graduated increase to full athletic activity
Patients who had any concussive symptoms or signs should not return to play that day and are advised to rest. School and work activities, driving, alcohol, excessive brain stimulation (eg, using computers, television, video games), and physical exertion should be avoided during early recovery to prevent prolongation or exacerbation of the symptoms (1).
Family members are advised to watch for signs of deterioration and take the person to the hospital if they occur. These signs include
Decreased level of consciousness
Focal neurologic deficits (eg, hemiparesis)
Worsening headache
Vomiting
Deterioration of mental function (eg, seems confused, cannot recognize people, behaves abnormally)
Seizures
Return to play
Typically, a graduated approach is recommended. Athletes should refrain from athletic activities until they are completely asymptomatic and require no medication. Then they may begin light aerobic exercise and advance through sport-specific training, noncontact drills, full-contact drills, and finally competitive play. Patients who remain asymptomatic at one level can be advanced to the next (2). (See also Heads Up: Returning to Sports).
But however quickly they improve, patients are typically advised not to return to full play until they have been asymptomatic for 1 week. Those who had severe symptoms (eg, unconsciousness for > 5 minutes, > 24 hours of amnesia) should wait at least 1 month.
Athletes who have had multiple concussions in 1 season need to be fully advised of the risks versus benefits of continued participation. Parents of school-aged children should be involved in these discussions as well.
Treatment references
1. Brown NJ, Mannix RC, O'Brien MJ, et al: Effect of cognitive activity level on duration of post-concussion symptoms. Pediatrics 133(2):e299–304, 2014. doi: 10.1542/peds.2013-2125
2. Patricios JS, Schneider KJ, Dvorak J, et al: Consensus statement on concussion in sport: The 6th International Conference on Concussion in Sport—Amsterdam, October 2022.
Prognosis for Sports-Related Concussion
Patients recover fully, although postconcussive symptoms can persist for up to several months.
Chronic traumatic encephalopathy causes progressive brain dysfunction typically leading to death within 10 to 15 years of initial presentation.
Key Points
Concussion involves transient, traumatic brain dysfunction; consciousness may be lost, but sometimes patients manifest only confusion, memory loss, and gait or balance difficulties.
Symptoms may resolve quickly or persist for up to several weeks.
Athletes with possible concussion should be removed from play and evaluated; screening tools such as SCAT5 may be helpful.
Neuroimaging is done if there is loss of consciousness, GCS < 15, focal neurologic deficits, persistently altered mental status, or clinical deterioration.
After concussion, patients are more susceptible to repeat concussion for a period of time and must refrain from sports activities until they have been asymptomatic for 1 week or more (depending on severity of injury).
Athletic activities are resumed gradually.
