Epidemiology of Traumatic Brain Injury

Marie Crandall

DEFINITION

Traumatic brain injury (TBI) occurs when there is a blow or jolt to the head due to rapid acceleration or deceleration or a direct impact. It can also be caused by direct penetrating injury of the brain. Brain function is temporarily or permanently impaired and structural damage may or may not be detectable [1]. Not all blows, bumps, or injuries cause TBI, and the severity of the injury may vary widely.

INCIDENCE AND PREVALENCE

Mortality

Injury is the leading cause of death for all individuals aged 1 to 45, accounting for more than 150,000 deaths every year in the United States, and more than 5 million deaths worldwide [2–4]. Head injury is responsible for the largest proportion of these deaths, contributing to one-third of all injury-related deaths [1,5]. The Centers for Disease Control and Prevention estimates that more than 50,000 people die from TBI every year in the United States [6].

Many patients with TBI will die shortly after their trauma, but mortality depends on a number of factors including age, severity and mechanism of brain injury, and presence of other injuries. The overall mortality of moderate-to-severe TBI is 21% at 30 days [7], and increases to 50% for severe TBI [8].

DISABILITY

Overview

The overall incidence of TBI is difficult to calculate because of differences in outcome measures, definitions, and reporting [9]. Estimates may include only TBI patients admitted to the hospital and may exclude patients presenting to nontrauma or non–emergency department (ED) practioners and/or ED visits that do not lead to admission, and typically do not include individuals who suffer injuries but do not seek medical attention. CDC data from 2010 suggest that 1.7 million people annually suffer TBIs. This can be thought of as a pyramid, with 52,000 deaths at the top, then 275,000 hospital admissions, and 1.4 million ED visits [5]. National Hospital Discharge Survey data, also from 2010, found 2.5 million TBIs occurring annually, either as an isolated injury or along with other injuries [6]. (The difference in estimates results from different sampling techniques.)

Mild TBI

The presentation and outcomes of TBI vary widely, from a brief loss of consciousness to permanent disability and death. Most TBIs are mild and do not cause permanent or long-term disability; however, all severity levels of TBI have the potential to cause significant, long-lasting disability [10]. The risk of permanent disability is low with mild TBI (MTBI), with most patients having complete resolution of posttraumatic symptoms by 3 months postinjury. However, up to 10% of patients, typically with a more severely impaired presentation and often with obvious intracranial pathology on imaging, may suffer persistent symptoms [11]. By contrast, permanent disability may be experienced by up to 65% of individuals with moderate TBI, and nearly 100% with severe TBI [12].

Approximately 75% of all brain injuries are concussions or MTBI [13]. Patients with MTBI may still suffer symptoms after the incident, including headaches, dizziness, inability to concentrate, and nausea. Up to 30% of patients will report posttraumatic symptoms, and some patients will have persistent complaints [14], although most of those with persistent symptoms do report improvement by 1-year postinjury [15].

Moderate-to-Severe TBI

Individuals with moderate-to-severe TBI may have significant impairments, and prognosis depends on the severity of injury [16]. However, up to 90% of patients with moderate TBI will be able to live independently, although many require assistance with finances, transportation, and more complex tasks [17]. Approximately 30% to 40% of people who have suffered severe TBI will make a good recovery, similar to that of moderate TBI [18]. The remaining patients may have profound and prolonged disability, existing in a permanent vegetative state or minimally conscious state, or have significant impairments, such as limited mobility or posttraumatic epilepsy. There is also a significant mortality risk, up to 10% at 6 months, mostly because of infectious complications.

Prediction of outcomes early after injury is based on logistic regression models including variables such as age, socioeconomic status, injury severity, biologic markers, and comorbidities, but these predictors are imperfect. Typically, younger patients, those with insurance, Caucasians, and those with less severe TBI and fewer concomitant injuries will have better outcomes [10,19]. Socioeconomic status also impacts the likelihood of receiving post-TBI rehabilitation, which affects both short- and long-term outcomes [19].

Costs

From a financial perspective, the costs of TBI are prohibitive. In 2000, annual TBI-related costs for acute and chronic care of patients were estimated at $60 billion [20].

DEMOGRAPHICS

Causes

Falls are the leading cause of TBI among all age groups (35.2%), followed by motor vehicle collisions or traffic accidents (17.3%), being struck by/against an object (16.5%), and assaults (10%) [6]. However, causes of TBI fatalities are slightly different. Among all causes of injury, road traffic accidents lead to the most TBI fatalities (31.6%). As another example, the lethality of gunshot wounds to the head is approximately 90%. Because of this, gunshot wounds are a much higher percentage of TBI fatalities than the overall incidence would suggest [13].

Risk Factors

The major risk factors for TBI are age, gender, and socioeconomic status. Infants and toddlers up to 4 years of age, older adolescents aged 15 to 19, and adults older than 65 years of age are the highest risk age groups for TBI [12]. This trimodal distribution has been demonstrated for most ethnic and racial groups studied, as well as in global studies of TBI [21–23]. Most studies have found that the highest age-specific incidence is in the young adult years. Injury and debility in this age group also carries significant morbidity, with many more years of potential life lost (YPLL) and lost productivity for injuries incurred in young people. For every age group studied, males are more likely to suffer TBI than females [24]. Among young people, males are up to seven times more likely to suffer a TBI [25]. People of color and those of lower socioeconomic strata also suffer rates of TBI 30% to 50% higher than majority individuals [25,26]. Alcohol is involved in 50% of cases of TBI, either because of intoxicated drivers or pedestrians, increased risk of falls, suicide attempts, or interpersonal violence [27–29].

SUMMARY

TBI is the leading cause of death among the injured, killing more than 50,000 people per year in the United States. Outcomes vary widely depending on mechanism of injury, age, and concomitant injuries or morbidities. Young males, people of color, and the socioeconomically disadvantaged are particularly at risk.

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