Mild Brain Injury Can Have Long-Term Effects

The consequences of mild traumatic brain injury are often anything but mild. Recent studies linking concussion to long-term neurologic deficits suggest that, for some individuals, the characteristic transient brain dysfunction and acute symptom resolution represent the beginning of potentially irreversible structural and functional brain alterations.

“Traumatic brain injury occurs as a spectrum disorder. The term 'mild' describes only the initial insult relative to the degree of neurological severity. There may be no correlation with the degree of short- or long-term impairment or functional disability,” said Dr. Nathan Zasler of the University of Virginia, Charlottesville, and medical director of the Concussion Care Centre of Virginia in Glen Allen.

By definition, mild traumatic brain injury (mTBI) results from direct trauma to the head or from an acceleration/deceleration stress to the brain. Such an injury poses a risk for short-term symptoms including headache and difficulty with balance, thinking, concentrating, and sleeping, and may lead to long-term symptoms categorized as postconcussive syndrome, according to the National Institute of Neurological Disorders and Stroke.

Investigators at the University of Illinois at Urbana-Champaign showed that college athletes with a history of sports-related concussion continue to have diminished brain function for a number of years after their injuries (J. Neurotrauma 2009 March [doi:10.1089/neu.2008–0766]). Specifically, “we were able to show that while our group of club and intercollegiate athletes performed normally on standard clinical neurocognitive assessment, they had suppressed brain functioning at an average 31/2 years post injury, including a decrease in attention allocation to things going on in their environment,” lead investigator Steven Broglio, Ph.D., said in an interview. The findings provide further evidence that concussion should not be considered a transient injury associated with short-lived neurologic impairment, he noted.

The authors of a widely reported Canadian case control study reached a similar conclusion. The study compared the neurocognitive status of currently healthy former university-level hockey and football players aged 50–65 years who had sustained a single concussion more than 30 years ago with that of former athletes with no concussion history. Electrophysiologic and neuropsychological tests indicated that individuals with a history of concussion had memory and attention problems along with slower reaction times relative to those of the controls (Brain 2009 Jan. 28 [doi: 10.1093/brain/awn347]).

At the more extreme end of the damage spectrum, biopsies of the brains of six former NFL players between the ages of 25 and 50 who had experienced multiple concussions during their careers revealed evidence of chronic traumatic encephalopathy, according to investigators at Boston University's Center for the Study of Traumatic Encephalopathy (CSTE). All six players had had emotional and behavioral problems such as drug abuse, and two committed suicide, said Dr. Ann C. McKee, lead investigator and CSTE codirector.

Mounting evidence of long-term effects of mTBI in athletes has led to growing concerns about the frequency of concussions among U.S. soldiers in Iraq and Afghanistan. An anonymous survey of more than 2,500 active duty and reserve soldiers conducted 3–4 months after a year-long tour of duty in Iraq showed that mTBI, when associated with a loss of consciousness, led to an increase in posttraumatic stress syndrome, relative to soldiers who had sustained other types of injuries or no injuries (N. Engl. J. Med. 2008;358:453–63).

Considering the large number of U.S. combat soldiers at risk for mTBI, the Department of Defense has mandated that all deploying troops undergo a cognitive functional assessment to serve as a baseline measure for comparison in case of later mTBI.

According to the Centers for Disease Control and Prevention, an estimated 5%–15% of individuals in the general population who sustain an mTBI have long-term deficits of some sort, although actual numbers are difficult to ascertain. “Not all people who sustain a mild brain injury recognize some of the later cognitive and behavioral impairments as related to the injury, and many don't seek medical treatment,” Dr. Zasler said. “This is why [mTBI] is sometimes called an invisible injury—people can look fine on the outside, but they may not be behaving fine, thinking fine, sleeping fine.”

Still, he added, most patients with single mTBIs recover relatively soon if they don't have comorbidities, or psychiatric or neurological histories that increase their vulnerability.

New evidence confirms suspicions that post mTBI problems are substantially underreported. Karen Hux, Ph.D., of the University of Nebraska-Lincoln and her colleagues evaluated a TBI screening procedure at vocational rehabilitation centers, domestic abuse and homeless shelters, and mental health centers. Of 1,999 screening protocols administered by professionals from four service agencies over a 6-month period, 531 were positive for a possible mTBI of sufficient severity to affect quality of life (Brain Inj. 2009;23:8–14).