Mild traumatic brain injury, also known as concussion, accounts for 80% to 90% of traumatic brain injuries and is recognized as a major national health concern.^1–7 Whereas 2.8 million traumatic brain injuries were reported in 2013,⁸ estimates suggest up to 3.8 million occur annually.^4,7,9 Concussion diagnosis and management can be challenging, complicated by the lack of a universal definition.^2,6,10 No single objective measure or combination of measures for diagnosis and no definitive evidence-based treatments exist. Return-to-activity and return-to-play decisions are limited by a shortage of prospective data.⁶ Physicians must rely on expert guidelines and available assessment tools with clinical judgment for diagnosis and treatment.^2,5,6

Definition, Signs, and Symptoms

Whereas no universal diagnostic criteria for concussion exist, there are commonalities across definitions. The most recent and commonly cited definition,^6,11 although primarily derived from research in the sports world, applies to all mechanisms of injury (Table 1⁶). Briefly, a concussion is a brain injury caused by a direct or indirect external mechanism with a clear temporal link to onset of symptoms.^2,12 However, other medical conditions (e.g., heat illness, exertional migraines), including preexisting conditions, cause similar symptoms as concussion and must be excluded.^{2,5,6,10,12,13}

Concussion affects multiple clinical domains: physical, cognitive, and emotional or behavioral. Common signs and symptoms are listed in Table 2.⁷ Headache is the most common postconcussion symptom, with a prevalence of 86% to 96%.^7,13 Dizziness, balance disturbances, and confusion or disorientation are also common.^7,13 Whereas loss of consciousness and amnesia were once considered the hallmarks of concussion, neither is required for diagnosis.^2,6

Pathophysiology and Natural Course

MECHANISM OF INJURY

Falls are the leading cause of concussions in adults and children, followed by being struck by an object or against an object and motor vehicle crashes.⁸ Estimates suggest that greater than 25% of concussions occur during sporting activities.⁹ In athletic settings, females are more prone to concussion.^4,6 Males are more likely to be injured through player-to-player contact, whereas females are more likely to be injured through contact with the playing surface or equipment.⁷

PATHOPHYSIOLOGY

Concussion results from rotational and angular forces to the brain.^7,13 Shear forces disrupt neural membranes, allowing potassium efflux into the extracellular space, causing increases of calcium and excitatory amino acids, followed by further potassium efflux and subsequent suppression of neuron activity.^7,12,13 As sodium-potassium pumps restore balance, a concomitant decrease in cerebral blood flow can result in an energy crisis.^7,12,13 Disruptions of autonomic regulation can persist for several weeks, during which time the brain may be vulnerable to further injury.⁷

RECOVERY

Symptoms of concussion typically present immediately after injury but can be delayed by minutes to hours^2,4,6; therefore, serial monitoring should occur after a potential concussion. Symptoms often resolve within 72 hours. Sports-related research reports that most adults (85% to 90%) fully recover within two weeks and children (70% to 80%) within one to three months.^5,6,14 Other literature suggests most adults recover within three months, with up to one-third experiencing prolonged symptoms.¹²

Factors predictive of recovery are poorly defined. Traditional markers (e.g., loss of consciousness, amnesia) do not have a clear association with prolonged recovery.⁶ The most consistent predictor of prolonged recovery is more severe symptoms immediately following injury.⁶ Other likely predictors include persistent neurocognitive impairment and history of prior concussion.⁴ Specific acute symptoms may also predict prolonged recovery: fatigue/fogginess and immediate or early onset of headache, amnesia, disorientation, or mental status changes.^4,6

Assessment Tools

None of the numerous assessment tools for diagnosis and management of concussion (eTable A) are exclusively effective.^3,4 Combining tools increases sensitivity and specificity.^4,6 Although the optimal combination is unknown, multidimensional tools are recommended based on expert consensus.^2,4,6 Comparing results of post-injury assessments with those of preinjury baseline testing is often conducted in athletes, although it is not mandatory.⁶ In younger children, baseline testing is not recommended because of significant variability over time and questionable prognostic value.⁵

SYMPTOM CHECKLISTS

Symptom checklists are useful for diagnosis and monitoring recovery. Checklists allow individuals to self-report symptoms, and they aid clinical decision-making throughout recovery.^2,6 Many self-report checklists with commonalities across measures are available, but none have been identified as the preferred choice.^4,6,10

NEUROPSYCHOLOGICAL TESTS

Neuropsychological tests identify cognitive deficits,⁴ but they are not well validated for concussion.^4,7,13 Such tests, however, may assist with return-to-activity or return-to-play decision-making and in evaluating individuals with prolonged symptoms.⁶ There is no consensus as to which neuropsychological tests are best, but those assessing attention, memory, and reaction time are the most sensitive for postconcussion sequelae.⁴

POSTURAL STABILITY TESTING

Because balance may be impaired by concussion, balance testing is recommended as part of postconcussion evaluation; however, the evidence regarding its utility is insufficient (i.e., low sensitivity).^2,4–6 Balance tests are most beneficial when used in combination with other evaluations.⁴

SPORTS SIDELINE ASSESSMENT TOOLS

Sideline tools are designed for use by clinicians and nonlicensed personnel. Common tools include the Standardized Assessment of Concussion and the Sport Concussion Assessment Tool 5 (SCAT5). These tools incorporate several assessment methods into a single instrument. The Standardized Assessment of Concussion is validated for junior high ages and older, with emergency department versions being validated only in adult populations.⁷ The SCAT5 is intended for athletes 13 years and older.^5,6 It is validated for use during the acute injury phase, although it has questionable utility three to five days postinjury.⁶ However, the incorporated symptom checklist may be useful for monitoring recovery.⁶ The Child SCAT5 is designed for children five to 12 years of age and incorporates simpler questions and assessments than the SCAT5, as well as a parent co-report, although it is not yet validated.^5,6 The tests in the SCAT5 series are widely used and are the most comprehensive sideline assessment tools available.

HOSPITAL ASSESSMENT TOOLS

Numerous tools are validated for clinical use.² Although a hospital version of the SCAT5 is not available, current versions can be modified for use in a hospital setting.⁶ The Centers for Disease Control and Prevention developed various versions of the Acute Concussion Evaluation for use in hospital, clinical, and emergency settings.¹⁵ The SCAT5 and Acute Concussion Evaluation series are available online (SCAT5: https://bjsm.bmj.com/content/bjsports/early/2017/04/26/bjsports-2017-097506SCAT5.full.pdf; Child SCAT5: https://bjsm.bmj.com/content/bjsports/early/2017/04/26/bjsports-2017-097492childscat5.full.pdf; Acute Concussion Evaluation forms for health care professionals: https://www.cdc.gov/headsup/providers/tools.html; and Acute Concussion Evaluation Care Plan for patients: https://www.cdc.gov/headsup/providers/discharge-materials.html).

Initial Evaluation

Figure 1 is a suggested algorithm for the initial evaluation of concussion.⁷ For obvious head injuries, assessment begins at the time of injury to evaluate the cervical spine.^2,5–7,13 In unconscious individuals, spinal injury must be assumed.^7,13 The initial assessment should first determine whether any emergent medical issues that require immediate attention have occurred. Evaluation should also clarify the severity of head injury, with more severe injuries referred for a higher level of care. Signs of more severe injury include loss of consciousness for more than 30 minutes, posttraumatic amnesia for more than 24 hours, and positive neuroimaging findings (Table 3⁷).

SPORTS SIDELINE EVALUATION

If concussion is suspected, an athlete should be removed from play and immediately evaluated by a qualified clinician.^2,4–6,13 After addressing urgent medical concerns, the clinician should assess the patient using a sideline assessment tool.⁴ Regardless of whether concussion is diagnosed or suspected, the athlete must not return to play before receiving medical clearance.^2,4–6,13

HOSPITAL OR CLINIC EVALUATION AND IMAGING

The hospital or clinic evaluation is similar to the sideline evaluation but encompasses a detailed history and neurologic examination.⁷ With concussion, findings are often subtle, and neurologic findings are typically normal other than mental status and balance deficits.^7,13 After emergent needs are addressed, a history of head injuries should be assessed. More conservative care (e.g., waiting longer for return to activity or return to play, earlier and more frequent follow-up) may be needed in individuals who have had multiple head injuries, especially if they occurred within the past year.

Imaging is not indicated for the evaluation of uncomplicated concussion.^{2,4–7,10,12,13} Imaging is important in excluding moderate or severe traumatic brain injuries, skull fractures, and spinal injuries but contributes little to the management of concussion because it is a functional rather than structural injury.^6,10 Computed tomography (CT) is the modality of choice.^2,10 Although magnetic resonance imaging (MRI) may acutely identify cerebral contusions, MRI is more appropriate for evaluation of prolonged deficits.² Plain radiography of the head has no role in the evaluation.^7,10,14

The most commonly used imaging guidelines for patients 16 years and older with mild head injury include the Canadian CT Head Rule¹⁶ and the New Orleans Criteria.¹⁷ Both guidelines are sensitive, but the Canadian CT Head Rule has higher specificity.^18–21 The Pediatric Emergency Care Applied Research Network (PECARN) pediatric head injury/trauma algorithm is validated for use in all children and adolescents through 18 years of age.^5,14,22,23 The Canadian CT Head Rule and PECARN algorithm are provided in eTable B. Free calculators are available at https://www.mdcalc.com/canadian-ct-head-injury-trauma-rule and https://www.mdcalc.com/pecarn-pediatric-head-injury-trauma-algorithm. Newer imaging modalities (e.g., functional MRI) are limited to research and do not yet have clinical application.⁶

BIOMARKERS AND ASSESSMENT DEVICES

Several assessment devices to help guide decisions about obtaining a CT scan (e.g., Banyon Brain Trauma Indicator,²⁴ Brainscope,²⁵ Infrascanner²⁶; eTable B) have recently received approval from the U.S. Food and Drug Administration. Whereas popular media often portray these assessments as tests for concussion, they actually function as indicators of possible acute intracranial lesions. The clinical utility of such devices is yet to be determined.

Management

INITIAL MANAGEMENT

Management of concussion is summarized in Table 4.^{1–7,10,13,14} Once medically stable, the patient may be released to home care provided that the patient has a responsible caretaker and access to medical care.⁷ Patient education, reassurance, and written instructions of when and how to seek medical attention are required at discharge. Education regarding basic facts of concussion, in written form and reinforced verbally, and reassurance that complete recovery is expected are among the most important aspects of concussion care.^5,10,12,14

Initial management after concussion includes a brief period of rest, followed by gradual return to activity. The ideal amount or duration of rest is supported only by limited data, but most guidelines suggest at least 24 to 48 hours.^{2,5,6,12,27,28} Extended cognitive and physical rest were once the cornerstone of initial management; however, this approach is impractical and may lead to prolonged symptoms and feelings of anxiety and isolation.^5,12 A recent study demonstrated that five days of strict rest provided no benefit over 24 to 48 hours of rest and was associated with an increase in reported symptoms.²⁹

No pharmacologic therapies are specifically available for concussion; therefore, medications for symptom management should be used as in patients without concussion.^6,7,10,12,13 Nonsteroidal anti-inflammatory drugs are commonly avoided in the first 72 hours after a concussion because of a theoretical risk of bleeding⁷; however, this concern has not been substantiated. Medications that mask worsening symptoms, such as high-dose analgesics, or that interfere with interpretation of mental status changes, such as sedatives, should be avoided.⁷

GRADED RETURN TO ACTIVITY

An individualized approach to return to activity is favored over rigid guidelines, and most algorithms allow for patients to progress at various rates.^2,5,6,13 After an initial rest period of at least 24 to 48 hours, patients should be encouraged to gradually return to their normal daily routines, such as school, work, and leisure activities, as tolerated.^{6,10,12,14,30–33} Recent evidence suggests that gradual increase of activities that do not trigger symptoms is safe and may expedite recovery.^6,12 Patients may return to unrestricted activities once they have fully recovered and are no longer taking medications that may mask symptoms.⁶

PROLONGED SYMPTOMS

A multidisciplinary approach should be considered for those with prolonged symptoms, including referral to a physician experienced in concussion management and for formal neuropsychiatric testing. Interaction with employers, teachers, or coaches may be necessary to ensure appropriate accommodations.

Special Considerations

CHILDREN AND ADOLESCENTS

Most concussion research applies to those 13 years and older; few assessment tools have been validated in children younger than 13 years.^5,6 Data suggest that teenagers are at greater risk of prolonged recovery.^5,6,14 Other risk factors for persistent symptoms include prior concussion, premorbid concussion-like symptoms, psychological or neurologic disorders, learning disabilities, Hispanic ethnicity, and lower socioeconomic status.¹⁴ Those presenting with severe or numerous symptoms after concussion may also experience persistent symptoms.^6,14 Children and adolescents with these risk factors should be monitored closely ¹⁴; however, given concern for potential consequences of injury to the developing brain, conservative management is recommended in all children and adolescents.^4,5,7,13,28 Recommendations for return to activity or return to play are similar to those for adults; however, guidelines recommend waiting until the child or adolescent has successfully tolerated returning to school before resuming full activity or play.^5,6

MULTIPLE CONCUSSIONS

There is conflicting evidence regarding the long-term effects of multiple or repetitive concussions.⁶ It is established that those with previous concussions have increased vulnerability to recurrent injury and typically experience longer recovery periods.^4–6,13 No specific guidelines exist regarding athletic disqualification or retirement because of recurrent concussions; however, more conservative management is recommended for those with recurrent concussions or increased sensitivity to impact.⁷

Prevention

The use of protective gear for preventing concussions is supported by limited evidence. Helmets and mouth guards reduce the risk of overall head and dental injuries, but neither has demonstrated a clear reduction in concussion incidence in most sports.^4–7 There is evidence that changing rules in some sports, such as restricting body checking in youth hockey, may reduce concussions.^4,6 Preventive education, such as the Centers for Disease Control and Prevention's Heads Up campaign (http://www.cdc.gov/HeadsUp), may enhance adherence to safety rules in sports, discourage overly aggressive playing styles, and allow for early recognition of symptoms.⁵ In 2009, the state of Washington enacted the Zackery Lystedt Law requiring concussion education for coaches, athletes, and parents and mandating removal of athletes from activity following suspected concussion, with clearance by a licensed clinician required to return to play. All 50 states now have similar legislation.^9,13,33

This article updates previous articles by Scorza, et al.⁷ ; Kushner³⁴ ; and Harmon.³⁵

Data Sources: A preliminary review was performed using Essential Evidence Plus. A PubMed search was completed in Clinical Queries using the key terms consensus statement concussion, consensus statement mild TBI, clinical practice guidelines concussion, clinical recommendations concussion, clinical recommendations mild TBI, diagnosis of concussion, diagnosis of mild TBI, evaluation of concussion, evaluation of mild TBI, management of concussion, management of mild TBI, treatment of concussion, and treatment of mild TBI. The search included meta-analyses, randomized controlled trials, clinical trials, and reviews. Also searched were the Cochrane database, Clinical Evidence, National Guideline Clearinghouse, Agency for Healthcare Research and Quality Evidence Reports, and UpToDate. Search dates: November 13, 2017; March 26, 2018; and February 12, 2019.

The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U.S. Army Medical Department or the U.S. Army Service at large.