ARTICLE IN BRIEF
INCREASED RADIAL DIFFUSIVITY SHOWN HERE (A) in soccer players in the right orbitofrontal white matter, the genu and anterior portions of the corpus callosum, association fibers involving bilateral inferior fronto-occipital fasciculus, bilateral optic radiation, and bilateral anterior cingulum, right anterior, right superior, and bilateral posterior corona radiata, right anterior limb of the internal capsule, right external capsule, and right superior frontal gyrus (A)
Invesigators contend that the white matter changes on diffuse tensor imaging of young professional soccer players revealing mild traumatic brain injury are likely due to repeating subconcussive “heading” of the ball.
Researchers from Harvard School of Medicine and Brigham and Women's Hospital in Boston have found evidence of changes in white matter integrity consistent with mild traumatic brain injury (TBI) in a small group of young, asymptomatic professional soccer players.
The changes are most likely due to repeated subconcussive “heading” — the sport's ubiquitous passing of the ball using only the head, and suggest possible demyelination, according to a research letter published in the Nov. 14, 2012, Journal of the American Medical Association.
“There have been some studies using conventional imaging, but this is the first case control study in soccer players using advanced neuroimaging like diffusion tensor imaging (DTI) in players without any symptoms or history of concussion but who have experienced repeated subconcussive blows to the head,” said lead author Inga K. Koerte, MD, a visiting senior research fellow in the Psychiatry Neuroimaging Laboratory at Brigham and Women's Hospital of Harvard Medical School.
“While we don't yet know what these changes in white matter diffusivity mean, they are similar to those observed in football and hockey players,” she told Neurology Today in a telephone interview.
She and Martha Shenton, PhD, professor and director of the Neuroimaging Laboratory and co-chair of the Research and Development Committee at the Veterans Administration Boston Healthcare System, evaluated 12 members of a professional German soccer club, and compared the findings with a matched group of professional competitive swimmers.
Whole-brain spatial statistics were obtained using sequences of 64 diffusion directions, and the team compared radial diffusivity, axial diffusivity — which measure axonal and myelin pathology — as well as fractional anisotropy, and mean diffusivity, both considered sensitive markers for mild TBI.
The imaging findings were then adjusted for the age of players and years of training. Most soccer players had been “groomed” for professional competition since childhood. Their mean age was 19 years and they had been competing, on average, for 13 years.
EVIDENCE OF RADIAL DIFFUSIVITY
The researchers discovered increased radial diffusivity in the right orbitofrontal white matter, the genu and anterior portions of the corpus callosum. They also reported radial diffusivity in fibers involving the bilateral inferior fronto-occipital fasciculus; bilateral optic radiationand bilateral anterior cingulum; right anterior, right superior, and bilateral posterior corona radiata; right anterior limb of the internal capsule; right external capsule; and right superior frontal gyrus.
Further analysis showed significantly higher radial and axial diffusivity in soccer players, although no significant relationship was found either between players' ages or years of training.
The study had a number of limitations, Dr. Koerte noted. There were few players evaluated and data were lacking in functional outcomes.
Nonetheless, clinicians who were not involved in the study said the findings are noteworthy. The study provides additionalpreliminary evidence that subconcussive trauma due to soccer heading may lead to brain injury pathology, said MichaelLipton, MD, PhD, associateprofessor ofneuroradiology at Albert Einstein College ofMedicine in New York, and director of Radiology Research at Montefiore Medical Center.
“These intriguing findings underscore the pressing need for larger studies, which quantify exposure and its relationship to functional outcomes, toward understanding the public health implications of this extremely common activity,” he told Neurology Today.
Research on the effects of soccer heading is limited and conflicting, the researchers noted. While some retrospective studies have suggested that it can contribute to impairment, prospective controlled studies have yet to find any link, and a number of other factors can also contribute lower neuropsychological scores.
However, the changes in white matter diffusibility were similar to those observed in profesional football and hockey players with histories of concussions, noted co-author and advisor Martha Shenton, PhD, professor and director of thePsychiatry Neuroimaging Laboratory and co-chair of the Research and Development Committee at the Veterans Administration Boston Healthcare System.
“We know that playing American football can lead to chronic traumatic encephalopathy, but not all professional American football players end up with this kind of damage to the brain,” she told Neurology Today. “The real question is what is the long-term impact on soccer players and when does it become a real problem. Right now, the answer is unknown.”
NEED FOR FURTHER RESEARCH
Additional research will be required, both to confirm the findings and to better understand the etiology and effects of the anomalies, the researchers noted, and there is a need to educate soccer players that they may be putting themselves at some risk for developing brain injuries and to be aware of symptoms.
Dr. Koerte cited a 1998 study in Dutch professional soccer players which found significantly lower scores on neuropsychological examinations than among a similar group of professional athletes not involved in sports involving head impact.
Published in Neurology, the study found impaired performances in memory, planning, and visuoperceptual processing in soccer players when compared with control subjects, with an inverse relationship depending on the number of past concussions and the estimated number of times players headed the ball.
“What is pretty striking is that the parts of the brain responsible for these skills are exactly where we found changes in white matter,” she said.
In Europe and other parts of the world, she continued, children start training to become professional soccer players at a very early age, although specific training of heading usually does not start before age 15.
Different studies measuring the velocity of soccer balls also raise concerns, she continued, with one showing head impact velocity of between 20 and 30 g. [The measure “g” here refers to g force acceleration as a measure of speed and mass of the ball.] Another study, published earlier this year studied ball velocity in a small group of girls' youth soccer players and found that head impacts ranged in peak linear acceleration from 4.5 g to 62.9 g.
“This is comparable to the force of a head impact in professional football, so it is very important to have a better understanding of any brain changes and neurocognitive problems in younger players as well,” said Dr. Koerte.
The DTI images allow us to show patients the brain images from repeated head impacts, something that our CT and MRI scans have not allowed us to do, said J. Scott Delaney, MD, research director in the department of emergency medicine and the McGill University SportMedicine Clinic, in Montreal, Canada. “Now I can actually show them what is wrong, and it really hits home with patients.”
Research should focus on the cumulative effects of repeated head impacts at the subconcussive level in soccer players, he said. But studying such athletes can be very difficult.
“We know from clinical studies that athletes typically do not volunteer for brain research or are unaware that they have suffered subconcussive brain injury, so we are only aware of perhaps 20 percent of the injuries and of these, many players do not come forward for a number of reasons.”
These injuries in younger players are a particular concern, because some studies have suggested that they are at risk when ball speed and velocity is much lower than in older athletes, and children and adolescents take longer to recover from brain trauma, he explained.