Clinical Context

The issue of subacute head injury in sports has caught the attention of the larger public, particularly in cases of damage to children and adolescents. There is increasing evidence that even subacute head trauma, not associated with concussion, can produce deleterious functional and even anatomic effects on the central nervous system.

Two studies address this issue. The first, by Whitlow and colleagues,^[1] observed 25 male youth football players between 8 and 13 years old for the 2012-2013 season, with magnetic resonance imaging (MRI) performed before the season and at the end of the season. Children with a history of concussion during the season were excluded from study participation.

The results of this study have been published online October 24, 2016, in Radiology. The researchers found that there were changes in functional anisotropy, which is used to measure axonal diameter and myelination, in comparing preparticipation MRI with postseason MRI. These changes were most prominent in the inferior fronto-occipital fasciculus.

The second study, by Stewart and colleagues, evaluates the objective effects on brain function after a heading exercise among soccer players.^[2] The results of this study are summarized in "Study Highlights."

Study Synopsis and Perspective

Head impact exposures during youth and young adult sports are associated with acute changes in brain function, and with cognitive impairment -- even in those who do not receive concussions, suggests 2 new studies.

The first included 25 boys 8 to 13 years old. During just 1 single season of football, there was a significant association between subconcussive head impact and fractional anisotropy changes in white matter tracts, as shown with diffusion-tensor imaging.

"There's expert consensus that concussions are bad for the brain. But we wondered about all the other head impacts that can occur that don't lead to a concussion and questioned: should we be worried about them?" coinvestigator Christopher T. Whitlow, MD, PhD, associate professor and chief of neuroradiology at Wake Forest School of Medicine in Winston-Salem, North Carolina, told Medscape Medical News.

"We were able to detect a very subtle change in the white matter of the brain. But we don't yet know whether this persists over a long period of time," said Dr Whitlow. The findings were published online October 24 in Radiology.^[1]

The second study, which was published online October 22 in EBioMedicine and examined 19 adult amateur soccer players,^[2] showed a significant increase in corticomotor inhibition immediately after routine head-butting of a ball, which was the primary outcome measure.

Reductions in memory were also found, but this result, as well as the primary finding, normalized 24 hours after the "heading" event.

Although the changes in brain function were transient, "these effects may signal direct consequences of routine soccer heading on (long-term) brain health which requires further study," write the researchers.

Coinvestigator William Stewart, MD, Department of Neuropathology at Queen Elizabeth University Hospital at the University of Glasgow, Glasgow, United Kingdom, noted that both studies should be treated with caution because of the low numbers of participants.

"So 'take-home messages' are hard to extrapolate," Dr Stewart said to Medscape Medical News.

However, "taking all we currently know, I think we can say there is enough in the data to date to suggest we should be limiting 'voluntary' exposure to head impact as much as possible, whenever at all possible."

Football Affects White Matter Integrity

The first study included 25 participants in a youth football league (mean age, 11.7 years) who played the sport during the 2012-2013 season. None had a clinically diagnosed concussion.

The Head Impact Telemetry system recorded head impact data, which was then "quantified as the combined-probability risk-weighted cumulative exposure (RWE_CP)," report the investigators.

The system is placed on the sidelines of a field during play and is fed real-time data from sensors embedded into padding gaps in the players' helmets. All participants also underwent MRI.

Seasonal fractional anisotropy changes were assessed in the following white matter tracts: inferior fronto-occipital fasciculus, superior longitudinal fasciculus, and inferior longitudinal fasciculus.

Results showed a significant association between RWE_CP and decreased fractional anisotropy in the left inferior fronto-occipital fasciculus (P =.003), as well as in that tract's core (P =.007) and terminals (P <.001) and in the right superior longitudinal fasciculus fiber terminals "where white matter and gray matter intersect" (P =.03).

Associations between impact exposure and decreased fractional anisotropy in the whole right superior longitudinal fasciculus missed significance (P =.08). There were also no significant associations with changes in the inferior longitudinal fasciculus.

Overall, the results suggest that "an increase in subconcussive head impact exposure may have an effect on WM [white matter] integrity in youth athletes," write the investigators.

"This study adds to the growing body of evidence that a season of play in a contact sport can result in brain changes at MR imaging, even in the absence of concussion."

Dr Whitlow noted that the fractional anisotropy decreases were especially interesting because similar changes have been reported in cases of mild traumatic brain injury. However, there are still many questions, including whether the changes go away or whether more changes occur with more seasons of play.

"I think this has made us more aware that we need to do more research to figure out what all of this means," he said.

Soccer Heading Impact

Of the 19 young adults (mean age, 22 years) in the second study, 5 were women. All headed 20 soccer balls that were launched by using a machine at standardized speeds during 10-minute sessions.

Measures of transcranial magnetic stimulation (TMS) were taken before the heading and immediately afterward, as well as 24 hours, 48 hours, and 2 weeks afterward, to assess corticomotor inhibition.

This outcome is "expressed by a longer period of electromyographic silence (cortical silent period -- cSP), after a motor evoked potential...is delivered to the primary motor cortex during contraction," the authors write. Cognitive function and cortical excitability were among the secondary outcomes measured.

Results showed that 14 participants (74%) had a measurable increase in corticomotor inhibition immediately after the heading sessions, with a mean increase in cortical silent period duration from 117.8 to 123.1 milliseconds (P <.05).

Error scores were also significantly higher on the Spatial Working Memory subtask of the Cambridge Neuropsychological Test Automated Battery (CANTAB) cognitive assessment tool (P =.03), which signified short-term memory impairment.

In addition, there a significant increase (by 67%) in error scores on the CANTAB's Paired Associated Learning task (P =.007).

All of these increases, however, went back to near-baseline readings at all subsequent follow-ups. In addition, TMS did not show significant changes in corticospinal excitability at any time point.

Electrophysiologic, Cognitive Impairments

"Sub-concussive head impacts routine in soccer heading are associated with immediate, measurable electrophysiological and cognitive impairment," write the researchers.

"[A]lthough the magnitude of the acute changes observed was small, it is the presence of the effect that is of interest," they add.

Dr Stewart noted via email that this was essentially a pilot study to establish protocols, and the investigators did not expect so few participants to yield strong data. "I'd be the first to admit that, given these (relatively) small numbers and (relatively) low exposures, I expected that we'd find nothing."

He added that they are now planning "many, many follow-up studies" to assess the effects from a larger study population, age, brain changes during a season, and a greater number of repeated exposures.

He also noted that even with the small numbers, as a parent he would interpret the current study to suggest, at the very least, "that heading should be avoided if you want your brain to be firing on all cylinders at any time in the following 24 hours. Exam on Wednesday? No heading on Tuesday."

When asked about the study from Dr Whitlow and colleagues, Dr Stewart said "it is far from the first of its kind and, I suspect, won't be the last."

"We've seen similar studies showing white matter changes across a season in sport. What it means is the question."

The study by Whitlow and colleagues was supported by grants from the National Institutes of Health. The study by Stewart and colleagues was supported by the National Institute for Health Research Brain Injury Healthcare Technology Cooperative and by existing funding awarded as part of the Framework 7 programme of the European Union. Dr Whitlow has disclosed no relevant financial relationships. Disclosures for the coauthors are available in the original study. Dr Stewart and his coauthors have disclosed no relevant financial relationships.

Radiology. Published online October 24, 2016.

EBioMedicine. Published online October 22, 2016.

Clinical Implications

• A study by Whitlow and colleagues found changes in fractional anisotropy in comparing brain MRI studies before vs after a season of youth football. These changes were most prominent in the inferior fronto-occipital fasciculus.
• Repetitive heading of a soccer ball was associated with increases in corticomotor inhibition and memory deficits immediately after the exercise in the current study by Stewart and colleagues, but any effect from the heading exercise resolved by 24 hours. Heading did not affect corticospinal excitability, attention, or processing speed.
• Implications for the Healthcare Team: Many players and their caregivers have questions regarding potential cortical damage in contact sports. The current studies serve as reminders that concussion may not be the only risk for athletes, and the healthcare team should provide appropriate perspective on this issue.

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