Concussion

Etiology

A concussion occurs as a result of either a direct or indirect injury to the head. Providers often consider a direct, traumatic blow to the head as a significant cause of a concussion. However, indirect traumatic forces elsewhere in the body can lead to an acute acceleration/deceleration injury to the brain, which can also lead to a concussion.[2]

Epidemiology

In the United States, each year, there are an estimated 1.7 million traumatic brain injuries that prompt presentation to the emergency department.[3] The Centers for Disease Control also estimates that when accounting for outpatient visits for TBIs and patients not seeking care for injuries, the actual incidence may range from 1.4 to 3.8 million concussions per year.[3] Frequent causes of concussions are motor vehicle crashes, being struck by an object, assault, and participation in recreational athletics. Although sports-related concussions make up a small percentage of overall concussions, much of the current research surrounding concussions stems from data on sports-related head injuries. Football consistently accounts for the highest number and percentage of athletics-related concussions in high school and college athletes. At the same time, soccer is responsible for the highest percentage of concussions in female athletes.[4] Female athletes suffer concussions about twice as often as male participants in the same sport.[4]

Pathophysiology

The pathophysiologic mechanism of a concussion is complex. The acute symptoms of a concussion are due primarily to a "functional disturbance rather than structural injury."[2] "Neurochemical and neurometabolic events" after an injury to the head result in an alteration of neurologic function.[5] Acceleration, deceleration, or rotation of the head results in acute axonal injury via disruption of neurofilament organization. The release of electrolytes through ion channel depolarization leads to a release of neurotransmitters and subsequent neurologic dysfunction. Changes to glucose metabolism decrease cerebral blood flow, and mitochondrial dysfunction also occurs.[5]

History and Physical

Assessment of a patient with a possible concussion should include gathering information on the mechanism of injury, the symptoms the patient is experiencing, the timing of symptom onset, and the severity and persistence of symptoms. The symptoms of a concussion can be wide-ranging but often fall into 1 of 4 main domains listed below. Some of the most common symptoms seen with concussion within each domain include:

1. Affective/emotional function

• Irritability
• Changes in mood

2. Cognitive function

• Confusion/disorientation
• Amnesia
• Mental fogginess
• Difficulty concentrating

3. Physical/somatic symptoms

• Headache
• Dizziness
• Difficulties with balance
• Visual changes

4. Sleep

• Drowsiness
• Sleeping less than usual
• Sleeping more than usual
• Difficulty falling asleep

The Sports Concussion Assessment Tool 6 (SCAT6) comprehensively examines possible concussion symptoms.[6] Most patients (greater than 90%) diagnosed with a concussion do not have an associated loss of consciousness [7]; however, loss of consciousness is an important sign of a potentially serious head injury.[8] Additionally, developing symptoms related to a concussion does not always occur immediately after an injury.[6] The development of symptoms within hours to days after a precipitating injury may still indicate a concussion. Of particular importance in a patient's history is whether the patient has a history of any prior concussions. "A greater number, severity, and duration of symptoms" with previous concussions can be predictive of longer recovery time.[1]  Finally, pre-existing mood disorders, learning disorders, sleep disturbances, and migraine headaches may also impact the management of a concussion.[1]

A physical examination specific to concussions should include:

• Close examination of the head and neck area for any structural injuries
• A thorough neurologic exam, including an assessment of strength, sensation, and reflexes; ocular assessment (including saccades and nystagmus); and assessment of a patient's balance and vestibular system
• Evaluation of a patient's cognitive function, including formally assessing orientation and higher-level cognitive processing
• An assessment of the patient's emotional state, including a comparison of the patient's current emotional state to their baseline with the patient's family or friends, if possible[2][9]

Formal neuropsychological assessment by a trained neuropsychologist can supplement a clinician's assessment of the multiple domains impacted by concussions.[2]

Evaluation

Diagnosis of a concussion remains an exclusively clinical diagnosis based on history and exam findings. However, there is no single pathognomonic finding or a minimum number of symptoms for diagnosing a concussion. Several standardized diagnostic tools can be employed in the pre-hospital setting following an acute head injury to assist in determining the presence of a concussion. The Sports Concussion Assessment Tool 6 (SCAT6) is 1 of the most commonly used tools for a concussion assessment, particularly by athletic trainers and sports medicine providers, to assess athletes on the sideline after a potential head injury. The Child SCAT-6 exists to assess patients between 5 and 12 years of age.[10] The optimal setting for administering these tools is a quiet setting that minimizes surrounding distractions.[6] Monitoring for the development of symptoms or any signs of neurologic deterioration after the initial post-injury assessment is necessary because of the potentially delayed presentation of symptoms and objective findings.[11] Signs and symptoms, including severe headaches, seizures, focal neurologic deficits, loss of consciousness, deterioration of mental status, and worsening symptoms, may indicate a more serious head injury and should prompt referral to an emergency department for further evaluation.[2]

Imaging modalities can be employed to rule out other injuries that may mimic the signs or symptoms of a concussion. In the hospital, a head CT scan is the radiographic study of choice for a quick evaluation to exclude neurosurgical emergencies.[12] Clinical decision tools, such as the Pediatric Emergency Care Applied Research Network (PECARN) head injury guidelines or the Canadian Head CT Rule, are often utilized to decide whether head imaging is warranted.[13][14] However, the majority of patients diagnosed with a concussion do not need head imaging.[15] Additionally, a normal head CT does not mean the patient has not suffered a concussion. Further radiographic investigation with an MRI is a consideration in patients with persistent post-concussive symptoms.[16]  Other imaging modalities, such as functional MRI or PET scan, are primarily used for research rather than clinical practice.[17] Testing for serum biomarkers of concussion is still under development but may have a role in future clinical evaluation.[18][19] If the symptoms are prolonged for more than 7 days, consider an MRI, which offers more details. Two promising serum biomarkers include ubiquitin C-terminal hydrolase and glial fibrillary acidic protein, which appear to be elevated early in the post-injury phase.

Treatment / Management

After diagnosing a concussion, an outpatient observation by a responsible individual educated on warning signs requiring further evaluation is generally appropriate. Patients with concerning signs or symptoms of more severe head injury may require continued hospital observation. Diagnosis of a concussion should prompt removing a patient from an environment that may lead to a repeat blow to the head (ie, immediate removal of an athlete from athletic participation).[2]

Treatment of a concussion is primarily supportive. Supportive care for concussion centers around the initial physical and cognitive activity limitation, followed by a gradual return to previous activity levels. There is no longer a role for extended, strict cognitive and physical rest.[9] While it is reasonable to encourage rest during the acute post-injury period (ie, the initial 24 to 48 hours), the patient should gradually return to activity. However, there is no optimal time for the initial rest period.[2] The patient should proceed with a stepwise return to activity with careful monitoring for the return or worsening of symptoms.[2] Recurrence of symptoms warrants a reduction in activity level until symptoms improve. Each increase in activity should generally take at least 24 hours, but again, there is no definitive evidence for the optimal timing of a return-to-activity protocol.[2] An athlete diagnosed with a concussion should be forbidden to return to play until cleared by a medical provider.

There is emerging evidence that early, targeted therapies and interventions aimed at specific clinical profiles of a concussion may be beneficial; however, evidence for identifying these clinical profiles and the efficacy of the therapy is still preliminary. Examples of these interventions include vision training for patients with oculomotor dysfunction or cognitive-behavioral therapy for mood disturbances.[9] 

Over-the-counter analgesics to control headache symptoms are an option, although there is limited evidence of their efficacy.[16] However, other medications that may alter a patient’s cognitive function, sleep patterns, or mood are not advisable as they may mask symptoms of a concussion. Preventive headache medications should not be initiated after a concussion but can be resumed if the patient was on them before an injury.[20]

Differential Diagnosis

The differential diagnosis immediately after a head injury should include potentially severe injuries, including cervical spine injury, intracranial hemorrhage, or skull fracture.[11] The differential diagnosis for post-concussive symptoms shifts once outside of the window of the acute injury. Symptoms of a concussion can overlap with other potentially pre-existing chronic conditions such as [2]

• Headache disorders or migraines
• Mental health diagnoses such as anxiety, depression, or post-traumatic stress disorder
• Problems with attention, such as attention deficit hyperactivity disorder
• Sleep dysfunction

The clinician must distinguish whether a patient's symptoms result from a concussion, a product of any other pre-existing conditions, or are of a different etiology.

Staging

Current Guidelines

1. Imaging studies are not recommended for mild brain injury. One should weigh the risks of radiation exposure and sedation in children compared to the benefits of imaging.
2. Use age-appropriate scales to make the diagnosis and make appropriate referrals.
3. Assess risks for the recovery.
4. Educate the caregiver/parent on appropriate activity after the injury.
5. Parents should encourage the child to return to non-sporting activities gradually after 2 to 3 days.
6. No medication can speed up recovery.

Prognosis

The prognosis for a patient with a concussion is usually good, with symptom improvement in the first 1 to 2 weeks post-injury. Previous research indicated the recovery timeframe after a concussion was typically about 10 days. However, the 5th International Conference on Concussion in Sports recently relaxed the expected recovery timeframe for sports-related concussions, stating that most injured athletes clinically recover within a month.[2] The importance of recognizing a more variable recovery timeline for concussions also received emphasis in a 2013 expert consensus statement.[9] The severity of symptoms within the first few days after a head injury is the most consistent prognostic indicator.[2] At this time, there is no definitive predictor of recovery time from a concussion, and the anticipated recovery timeframe should be individualized for each patient.[9]

Complications

The most commonly seen complication of a concussion is post-concussion syndrome (PCS), characterized by persistent symptoms lasting weeks to months after the initial injury. The median duration of symptoms in 1 study was 7 months.[21] The transition from a concussion to the post-concussion syndrome is "ill-defined and poorly understood."[1] Any of the possible concussion symptoms can be present with post-concussion syndrome, but PCS characteristically presents with multiple "somatic, emotional, and cognitive symptoms."[22][23] The severity of the initial injury does not seem to correlate with the likelihood of developing post-concussion syndrome.[1] Still, a history of prior concussions does appear to correlate with the likelihood of the development of PCS.[22][21][23]

One of the most feared and concerning complications of a concussion, although rare, is a second-impact syndrome. Second-impact syndrome (SIS) involves a repeat blow or injury to the head before the complete resolution of the initial concussion, resulting in usually rapid, severe swelling of the brain.[24] SIS has the potential for dangerous neurologic complications, including brain herniation and death, though much of the existing data and research on the condition is anecdotal.[24][25] Research on the long-term consequences of a concussion is still limited. Of greatest concern is the potential for the development of chronic traumatic encephalopathy (CTE). This condition is characterized by slow, progressive neurodegeneration due to repeated head trauma and tau protein deposition.[26] Symptoms may include memory disturbances, behavioral or personality changes, and speech or gait abnormalities. The overall incidence and prevalence of CTE are unknown, and at present, CTE can only be definitively diagnosed with a neuropathologic examination.[26] Lastly, research has yet to establish a cause-and-effect relationship between concussions and CTE.[1]