A long overdue and growing body of research on concussions is providing today’s young athletes, parents and coaches with more information about identifying and treating head injuries—but not all of that research is reliable. For instance, one new study on youth concussions offers valuable information about recovery time, whereas potentially flawed conclusions in a second new study illustrate one of the biggest challenges in studying youth concussions—missed diagnoses.

An estimated 170,000 children go to the emergency room for concussions annually, but this number does not capture the millions treated outside of hospitals by athletic trainers, family doctors or specialists. The sports with the most reported concussions are boys’ football and girls’ soccer, but bicycling, basketball and playground activities are also among the most common ways children sustain these head injuries. Symptoms can include dizziness, fatigue, nausea, headache and memory or concentration problems. After a concussion is identified, the primary treatment is physical and cognitive rest, although the amount of rest needed is not always medically clear.

The first study, published June 10 in Pediatrics, found that recovery takes up to two or three times longer if a child has sustained one or more concussions within the past year, further supporting reasons “to be cautious about returning young athletes to sports after a concussion,” says lead author Matthew A. Eisenberg of Boston Children’s Hospital. Eisenberg’s study notes.

Yet, ensuring a child has more time to rest after sustaining an additional concussion is harder to do if the injury is not properly identified. In fact, an estimated 70 to 90 percent of concussions in sports are never diagnosed, say Robert Cantu and Chris Nowinski, co-directors of the Center for the Study of Traumatic Encephalopathy at Boston University.

Flaws in the methodology of the second study (pdf), published June 6 in the Journal of Pediatrics, inadvertently elucidate one way that happens. The study, led by Anthony P. Kontos at the University of Pittsburgh Medical Center, claims to find that fewer concussions occur during preteen football practices than occur during games, but Cantu and Nowinski say it really just shows how many concussions are missed during practices due to a lack of trained eyes on those fields.

Second and third hits worsen the prognosis

In Eisenberg’s study, 280 patients, aged 11 to 22, were examined for up to 12 weeks after ER treatment for concussion, defined as a head injury that alters mental status or is followed by any new symptoms within the subsequent four hours. About 64 percent of the concussions resulted from sports, primarily hockey, soccer, football and basketball.

Youths with no previously diagnosed concussions took a median 12 days for all their symptoms to resolve, whereas those with a history of any concussions took a median 22 days. It took about three times longer (median 35 days) for the patients to recover if their concussion had been within the past year. Recovery time more than doubled (median 28 days) if they had more than one past concussion.

Eisenberg’s findings confirm prior research on concussions in animals. Longer recovery times for second concussions could be explained by cumulative structural damage to the brain’s white matter. It is possible that injured brain cells “have not fully recovered, which may indicate that the window of recovery for the initial concussion is much longer than previously thought,” Nowinski says. A more useful analysis would also have taken into account the severity of subjects’ previous concussions and the time interval between multiple concussions, Cantu says.

It’s actually tricky to categorize concussions by the severity of symptoms. The widely used American Academy of Neurology’s clinical guidelines for sports concussions previously assigned one of three grades to concussions based on symptoms. Similar scales had been developed by the Colorado Medical Society and by Cantu, but these classification systems fell out of favor over the past decade as research revealed the grades did not correlate with recovery times. Also, using symptoms to determine severity can be misleading, says Daniel Clearfield, assistant professor of orthopedic surgery at the University of North Texas Health Science Center. For this reason and others, the American Academy of Neurology updated its guidelines in March (pdf).

Counterintuitive secondary findings

Two other findings in Eisenberg’s study reveal how little is still known about concussions. Kids younger than 13 recovered a little sooner (median 11 instead of 15 days) than kids older than 13—contradicting past animal studies’ findings—and youths who lost consciousness recovered a little faster (median 11 instead of 14 days) than those who did not lose consciousness. Younger players may recover faster because their parents may be more likely to bring them in for milder concussions, Nowinski says, or younger kids may be sustaining less severe injuries because the hits are not as hard as with older, bigger, stronger kids, Clearfield and Eisenberg suggest.

The loss of consciousness surprised Eisenberg but not Nowinski or Clearfield. Nowinski notes that kids who lose consciousness are more likely to go to the ER because the concussions are immediately recognized. “Most concussions that do not involve loss of consciousness are not immediately diagnosed,” Nowinski says. “Therefore, the athletes often finish the game, causing additional injury to the brain prior to beginning physical and cognitive rest.”

Eisenberg also suggested other possibilities for the finding about loss of consciousness, such as study bias: it could be that more kids with mild concussions involving brief loss of consciousness visited the ER, whereas kids who did not lose consciousness came in only if the concussion was particularly severe. It is also possible that those who lose consciousness may have better adherence to treatment plans and time off for recovery. Or, Eisenberg says, as in mice, “it may be that the mechanism that led you to lose consciousness may be different than the mechanism that causes you to experience the other symptoms of the concussion, but we can’t say based on our results alone.”

Second study muddies the waters

More research on youth concussions is clearly needed, Eisenberg and the other experts say. Yet, the Journal of Pediatrics study by Kontos was not helpful, Cantu says. The study recorded the number of concussions diagnosed among 468 western Pennsylvanian youth football players, aged eight to 12, during the 2011 season. Among more than 8,415 practices and 2,923 games, a total of 20 “medically diagnosed” concussions were reported, nearly all during games.

The authors concluded concussions are less common during practices than during games because the incidence rate of concussions was 25 times greater during games. But that’s the wrong conclusion, Nowinski and Cantu say. Both pointed out that the occurrence of only 20 concussions in more than 11,000 games and practices indicates “gross” underreporting, especially at practices where medical personnel and spectators are not present to watch the kids and only the worst injuries are likely to end up diagnosed.

“If you’re going to compare concussion rates at practices versus games, you have to have the same degree of scrutiny at practices as at games,” Cantu says. “There’s nobody at practice other than the coaches, and we don’t know if they know what a concussion is or not, and they can’t make the diagnosis.” Nowinski points to one past study’s finding that a trainer’s presence increases the incidence of concussions four to eight times and another that found doctors can identify up to seven times as many concussions as athletic trainers.

In fact, noting that the concussion rate in Kontos’s study for young players during games is two to three times higher than it is for older players during games, Nowinski said the study shows that football for eight- to 12-year-olds “is dramatically more dangerous than for high school and college players. Due to the lack of medical infrastructure at all levels of football below high school, this study shows there is more reason than ever to restrict full-contact practice.”

Together, the two studies offer a couple of takeaways. The potential biases in the first study and the low practice numbers in the second support prior findings that many concussions go unreported while also pointing to high incidence rates among youth. The Eisenberg study also reveals the challenges in assessing the severity of concussions, suggesting “that there cannot be an absolute set standard on how a concussion should be treated,” Clearfield says. And the “dose-response effect” in Eisenberg’s study—where more time is required to recover when more concussions have occurred in a patient’s history—offers more evidence of the potentially lifelong symptoms of multiple concussions. Athletes with multiple concussions at a young age, Nowinski says, should seriously consider switching to a sport in which concussions are less likely.