Traumatic Brain Injury More Common Than Previously Reported

Pauline Anderson

November 29, 2012

The incidence of traumatic brain injury (TBI) uncovered by a new study in New Zealand is much higher than some previous estimates.

The new report shows an incidence of 790 per 100,000, higher than previous reports for high-income countries in Europe (47 to 453 cases) and North America (51 to 618 cases). The higher incidence is probably due to the fact that this new study included mild TBI cases, which do not always lead to hospitalization but can still lead to disability.

Extrapolation of this figure to the world population suggests that every year, 54 to 60 million people have a TBI and some 2.2 to 3.6 million of them sustain a moderate or severe TBI.

"To our knowledge, this study is the first large population-based study to investigate TBI incidence across the spectrum of severity in all age groups in a geographical region with urban and rural populations," said the authors, led by Valery L. Feigin, MD, National Institute for Stroke and Applied Neurosciences, AUT University, Auckland, New Zealand.

"Our age-specific and residency-specific data for TBI incidence overall and by mechanism of injury should be considered when planning prevention and TBI care services," they conclude.

The study was published online November 22 in The Lancet Neurology.

Capturing Data

The Brain Injury Outcomes New Zealand In the Community (BIONIC) was a large population-based study undertaken in New Zealand during 2010-2011. Researchers used various databases and surveillance systems to capture all TBI events among urban residents of the city of Hamilton and rural residents of Waikato District (a total population of more than 170,000) within a 1-year period.

The researchers made every effort to capture data for all individuals with mild TBI who were not admitted to the hospital by including those from family practices; by checking death certificates and accident records of community health services, schools, sport centers, and rest homes; and by widely advertising the study within the region of interest.

TBI was defined according to World Health Organization criteria as an acute brain injury resulting from mechanical energy to the head from external physical forces, with presence of confusion, disorientation, loss of consciousness, and/or post-traumatic amnesia.

Mild TBI was a Glasgow coma scale (GCS) of 13 to 15 or post-traumatic amnesia (PTA) within 24 hours of injury, moderate TBI was a GCS of 9 to 12 or PTA within 1 to 6 days of injury, and severe TBI was a GCS of 8 or lower or PTA 7 or more days from injury.

The overall incidence of TBI was 790 per 100,000 (95% confidence interval [CI], 749 - 832). This is higher than previous reports for high-income countries in Europe (47 - 453 cases) and North America (51 - 618 cases), probably because of the multiple overlapping sources of information used on a population level.

"Much of the discrepancy between estimates is accounted for by the fact that we included people with mild TBIs who were not admitted to hospital — such cases are often overlooked in hospital based studies," the authors write.

Of the 1369 individuals with TBI, most were boys and men younger than 35 years (69%). The incidence of TBI in males was almost twice that for females (relative risk [RR], for mild TBI, 1.73; 95% CI, 1.54 - 1.93; RR for total TBI, 1.77; 95% CI, 1.58 - 1.97).

Most TBIs Mild

Most patients with TBI were urban residents (74%) of European ethnicity (61%). The vast majority (95%) had mild TBI, with the risk of sustaining mild TBI more than 18 times greater than that for moderate or severe TBI. About a third of the patients (36%) didn't present to hospitals at the acute stage of TBI.

Falls (which accounted for 38% of TBIs), assaults (17%), exposure to mechanical forces, and transport accidents were the most common cause of TBI. TBI due to assaults was more common in adolescents and young adults of Maori ethnicity than in those of European descent.

"Clinicians dealing with patients with TBI should be aware of ethnic and sex disparities in TBI incidence when considering management and prevention strategies for such patients," said the authors.

The study found a greater than expected proportion of TBI in children and younger adults — they represented almost 70% of all TBI cases as opposed to the 40% to 60% reported elsewhere.

The small number of moderate and severe TBI cases precluded detailed analyses of these injuries as separate categories (they were combined). Another potential limitation of the study was that it recorded TBI events for only 1 year.

TBI is the leading cause of long-term disability in children and adults younger than age 35 years. Projections indicate that TBI will become the third largest cause of global disease burden by 2020.

In an accompanying editorial, Nada Andelic, MD, Division of Surgery and Clinical Neuroscience, Department of Physical Medicine and Rehabilitation, Oslo University Hospital, Oslo, Norway, said the study contributes an outline of the methodologic criteria for a population-based TBI incidence study that can be used in future TBI epidemiologic research.

National TBI surveillance systems are needed to monitor trends and develop appropriate preventive measures, control strategies, and effective TBI care, she wrote.

"A greater understanding of patient-specific characteristics is needed to reduce TBI risk at the individual level, and a focus on age, mechanism of injury, and severity-specific groups is needed to reduce the incidence of TBI at the population level," she concludes.

The study was funded by the Health Research Council of New Zealand. The authors have disclosed no relevant financial relationships.

Lancet Neurol. Published online November 22, 2012. Abstract Editorial