Mild traumatic brain injury (MTBI) and concussion are interchangeable terms representing a reportedly mild, non-penetrating traumatic injury associated with a brief alteration in brain function.¹ MTBI is one of the most common neurological conditions in the world,² and is a serious public health problem in the U.S.³ In 2010, a combined total of 2.5 million TBI-related emergency department visits, hospitalizations and deaths were reported. These TBIs were either an isolated injury, with TBI as the only injury, or present along with other injuries.⁴ It is estimated that MTBI accounts for 80–90% of all cases of TBI in both civilian⁵ and military populations.⁶ MTBI is most often treated in emergency departments (EDs) or in non-hospital medical settings, or it is not treated at all.³ While most adults and children recover within days to months, recent studies have shown that 15%–25% of these patients continue to report physical, cognitive, emotional, or behavioral symptoms up to one year post-injury.^7–11 Some people with MTBI have difficulty returning to routine daily activities and may be unable to return to work for weeks or months,¹² costing the U.S. economy an estimated $17 billion per year in 1995.³

To our knowledge, no nationally representative data have been used to describe the epidemiology of MTBI treated in EDs in the U.S. with the specific purpose of comparing isolated MTBIs and non-isolated MTBIs (i.e., those presenting with concurrent injuries or co-morbidities). Understanding the epidemiology and trends of MTBI treated in EDs may help design prevention and management strategies by targeting those at higher risk This information could be useful for health care resource planning and may help to improve patient outcomes. The purpose of this population-based descriptive study is to describe the frequencies and rates of MTBI ED visits, and analyze the trend across the years; and to compare sociodemographic characteristics of visits by MTBI type (i.e., MTBI as the only injury, or present along with other injuries).

The overall rate per 100,000 population of MTBI ED visits in the U.S. significantly increased from 569.4 (N=1,699,204) in 2006 to 807.9 (N=2,535,877) in 2012, with an AAPC of 7.0% (95% CI, 5.0–9.0; p=0.0002) (Table 1). Significant average annual increases were observed for both males (AAPC, 5.6%; 95% CI, 4.1–7.2; p=0.0002) and females (AAPC, 8.7%; 95% CI, 6.1–11.4; p=0.0003) (Table 1, Figure 1). Between 2006 and 2012, the AAPC significantly increased in every age group (all p<0.02). The age groups with the highest average annual rates of MTBI ED visits were 0–4 year olds (1417.7, 95% CI, 1331.0–1504.4) and 15–24 year olds (966.2, 95% CI, 924.6–1007.9); in contrast, 45–64 year olds had the lowest average annual rate (417.2, 95% CI, 398.9–435.5) (Table 1, Figure 2). Taking into account both age group and sex, the highest average annual rates of MTBI ED visits were observed in male 0–4 year olds (1592.8, 95% CI, 1494.7–1690.8), female 0–4 year olds (1234.8, 95% CI, 1159.6–1309.9), male 15–24 year olds (1127.4, 95% CI, 1079.6–1175.2), and females ≥ 65 years old (1005.0, 95% CI, 958.5–1051.6).

Overall, males had a significantly higher rate of MTBI ED visits than females (760.9, 95% CI, 729.4–792.5 vs. 622.6, 95% CI, 596.6–648.5; p<0.0001). This pattern was observed in all age groups except among those aged ≥ 65 years where females had a significantly higher rate than males (1005.0, 95% CI, 958.5–1051.6 vs. 712.3, 95% CI, 679.5–745.1; p<0.0001).

In total, during 2006 to 2012, the majority of MTBI ED visits were comprised of non-isolated MTBI (n=1,474,413; 69.6%). The aggregated annual average frequencies and percentages of MTBI ED visits, by MTBI type, and selected sociodemographic characteristics are reported in Table 2. Sex

Compared to females, males had a 4.0% lower odds of an ED visit for an isolated vs. non-isolated MTBI (OR, 0.960; 95% CI, 0.950–0.971; p<0.0001).

On average, we found that the MTBI ED visit rates in the U.S. increased significantly from 2006 to 2012 for both males and females in all age groups. The highest average annual rates of MTBI ED visits were observed in 0–4 year old males and females, followed by 15–24 year old males, and ≥ 65 year old females.

We also found that approximately 70% of all MTBI ED visits were non-isolated. Associated sociodemographic factors were: male sex; older patients (≥ 65 years); those injured by assault; non-metropolitan residence; low community-level income; non-private insurance; weekend ED admission day; and presentation to a non-teaching hospital, and to a hospital located in the South region.

Our findings agree with Marin et al who found that the rate of all TBI ED visits in the U.S. increased significantly from 2006 and 2010, with the rate being higher for males compared to females.²⁰ We used narrower age categories and also broke down each age category by sex, finding that females had a higher rate in the ≥ 65 year age group. One possible explanation from the literature is that fall-related injuries disproportionately affect the health and quality of life of older women.²¹ Other studies suggest this could be due to lower physical activity and reduced lower body strength in older women compared to older men²² as well as reduced bone mass in older women.^21,23

Marin et al found that children younger than 3 years and adults older than 60 years had the largest increase in TBI rates. Our results differed somewhat and are likely due to our use of narrower age categories in combination with sex. We observed the highest average annual rates of MTBI ED visits among 0–4 year old males and females, followed by 15–24 year old males, and ≥ 65 year old females. While we found that falls are the most common external cause of MTBI ED visits for all age groups, particularly in 0–4 and ≥ 65 year olds, the literature suggests that 15–24 year olds are also commonly afflicted by assault and MVT.²⁴ This is especially the case for males who are presumably engaged in more risk-taking behavior than females.²⁵ We found that 70% of MTBI ED visits were non-isolated (i.e., occurred with other injury or co-morbidity). Similarly, Marin et al²⁰ found that 40% of TBI visits had at least one other injury, including wounds of the head, neck, or trunk; sprains and strains; and fractures.

Marin et al further indicated that the TBI ED visit rate was 8-fold more than the rate of increase of total ED visits during the same 2006–2010 period.²⁰ We agree with their proposed explanation - that the increased rate of TBI ED visits may be related to increased TBI exposure, awareness, diagnoses, or a combination. Practice patterns and a lack of alternatives for care may also be contributing to increasing ED visits. For example, people may be unable to easily access primary care at certain times. The fact that more MTBIs are presenting to U.S. EDs²⁰ underscores the importance of appropriate resource planning and patient management for MTBI in EDs.

The literature suggests many MTBIs are underdiagnosed in U.S. ED settings.^26–28 Thus, our estimates of isolated and non-isolated MTBI ED visits in the U.S. may be lower than the true estimates, especially for non-isolated MTBI, because it may be more likely to be missed when the head injury is not the presenting concern. On the other hand, some MTBI visits may be captured in the ED because it is other injuries that bring them into the ED and not specifically the MTBI. We do not know how undiagnosed MTBI ED visits differ from those that are diagnosed, and there are likely many factors involved (e.g., busy ED nurses and physicians, lack of resources or tools to screen for MTBI, lack of incentive to document MTBI if not relevant for reimbursement, and concurrent presenting injuries or illnesses). Nonetheless, previous studies have stressed the importance of improving the recognition of MTBI in EDs in order to provide timely and appropriate patient management and follow up, and ultimately improve patient outcomes.^2,29 Our findings support this research suggesting that ED physicians should have a higher index of suspicion of MTBI in patients with other injuries.

Certain sociodemographic factors, namely male sex, lower socioeconomic status (i.e., lower community-level income), and older age may be associated with non-isolated MTBI for the following reasons. Other literature suggests that males, especially adolescents and young adults, have higher rates of injury-related visits to EDs in the U.S. than females.^30,31 This may be due in part to presumed increased risk-taking behaviour, participation in contact sports such as American football, and alcohol consumption. Explanations from other studies suggest that alcohol consumption is associated with physical assault, falls, and MVT, and these mechanisms increase the odds of concomitant injuries.³² Increased alcohol consumption and physical assault may also be more prominent among individuals with lower socioeconomic status. According to other studies, socioeconomic status is an important determinant of injury, e.g., blue-collar workers were found to be at significantly increased odds of nonfatal injury compared to white-collar workers.³³ Finally, other literature suggests that older adults (≥ 65 years) have higher rates of comorbidities, which may lead to falls,³⁰ and thus multiple injuries including MTBI.

The rate of MTBI ED visits in the U.S. increased significantly from 2006 to 2012, and the majority of these visits were for non-isolated MTBI. It is likely that many MTBIs, especially non-isolated, remain largely undiagnosed in U.S. EDs and we presented a number of associated sociodemographic factors that may facilitate their detection. This information has implications for ED resource planning; as well as for MTBI education and screening processes in EDs, especially in non-teaching hospitals located in the South.

This information also has implications for primary prevention. For instance, for the groups with the highest average annual rates of MTBI ED visits (0–4 year olds, 15–25 year old males, and ≥ 65 year old females), increased primary prevention efforts could be directed toward preventing Shaken Baby Syndrome (a form of abusive head trauma and inflicted TBI),³⁷ falls,³⁸ comorbidities (e.g., hypertension and diabetes mellitus), and motor vehicle traffic incidents, especially in non-metropolitan residences.

Finally, these data have implications for government-sponsored healthcare programs which cover seniors aged 65 years and older, and certain disabled individuals (i.e., Medicare), and low-income individuals (i.e., Medicaid); all of whom may be more exposed to MTBI, and non-isolated MTBI in particular. Concurrent injuries and illnesses could complicate or delay recovery of MTBI, potentially leading to more costly ED visits and number of ED visits, not to mention higher healthcare system costs altogether.

Our findings highlight the need for future research to develop accurate algorithms for identifying and coding MTBI and comorbid conditions in the ED. Future research should also assess the use of EDs versus other health care settings for MTBI.