Concussion (Mild Traumatic Brain Injury)

Concussion (Mild Traumatic Brain Injury) is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Concussion (or mild traumatic brain injury [mTBI]) is defined as a complex pathophysiologic process affecting the brain, induced by traumatic biomechanical forces. This can be direct (blow to the head) or indirect (impulsive force is then transmitted to the head).
  • Concussion may or may not involve loss of consciousness (LOC). There is currently no universally accepted classification system for concussions.
  • The most prevalent and consistent indicators are (1):
    • Immediate confusion or disorientation
    • Impaired balance within 1 day
    • Slowed reaction times within 2 days of event
    • Impaired verbal learning/memory within 2 days

Pediatric Considerations
Resolution of symptoms and return to neurocognitive baseline often takes longer in young athletes (<18 years).

Epidemiology

  • The CDC estimates 2.5 million concussions occur every year (many go unreported).
  • >1 million ER visits every year are due to TBIs (falls, MVAs, assault, sports, others); more than half of these visits are in young patients (aged 5 to 18 years).
  • Concussion rates have increased in young athletes over the past 30 years (partly due to increased reporting); highest incident sports: football, hockey, rugby, soccer, basketball
  • Concussions more likely in games than practices
  • Female athletes have more reported concussions than male athletes in similar sports and more frequently suffer cognitive impairment.

Incidence
  • The most common cause of TBI in the elderly (>65 years of age) is falls.
  • Up to 1/3 of all sports-related concussions may go unreported or undiagnosed (2)[B].
  • Sports (numbers per 1,000 athlete exposures, defined as one athlete playing in one game or practice)
    • Football: college 0.61 (0.39 in practice, 3.02 in games); HS 0.47 (0.21 in practice, 1.55 in games)
    • Basketball (college): males 0.16; females 0.22
    • Ice hockey (college): males 0.41, females 0.91
    • Lacrosse (college): males 0.26, females 0.25
    • Soccer: college males 0.49, HS males 0.22; college females 0.63, HS females 0.36
    • Skiing and snowboarding: 0.005 and 0.004, respectively. Snowboarders have a higher incidence of severe brain injuries than skiers.

Etiology and Pathophysiology

  • Direct or indirect injury to the head
    • Falls
    • Sports-related injuries
    • Motor vehicle accidents
    • Assaults
  • Identifiable metabolic changes include alterations in intra-/extracellular potassium, calcium, and glutamate with subsequent neuron dysfunction. Microtearing of cerebral blood vessels and a relative decrease in cerebral blood flow also occurs. An increased requirement for glucose by the brain, coupled with decreased blood flow, may result in cellular dysfunction and increased susceptibility to subsequent brain insults.
  • Structural abnormalities of the brain are typically absent based on imaging studies.

Risk Factors

  • Patients at high risk for falls: elderly, intoxication
  • History of previous concussion
  • Young adolescents, female gender
  • Contact sports (particularly football): activities such as bicycling, cheerleading, skiing, and snowboarding; organized sports > leisure physical activity
  • Severity predictor
    • Retrograde amnesia is better predictor than LOC for acute neuropsychological deficits (3).
    • Longer recovery in mood disorders, learning disabilities

General Prevention

  • Educate athletes, coaches, parents, and officials about signs and symptoms of concussions.
  • Preparticipation exams to identify at-risk athletes
  • Strength and conditioning (athletes and elderly)
  • Head-up tackle training reduces linear acceleration of the head but has not been shown to reduce concussions. Protective equipment (helmets, mouth guards) decrease overall injury rates but have not been shown to decrease concussion rates.

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