Evaluation and management of concussion involves many factors, some of which may predict the potential for prolonged or persistent post-concussion symptoms and long-term health effects.
The current international consensus of concussion experts ("Zurich consensus statement") (1) is that a range of "'modifying' factors may influence the investigation and management of concussion, and, in some cases, may predict the potential for prolonged or persistent symptoms, and in others suggest consideration be given to retirement from contact or collision sports:
| Factors | Modifier |
| Symptoms | |
| Signs |
Prolonged loss of consciousness (more than 1 minute duration) Amnesia (Note that amnesia was not found in two recent studies (6,7) to be predictive of longer recovery, adding to an already muddled picture as to the role amnesia plays in predicting concussion recovery) |
| Sequelae | Concussive convulsions (Note: it is puzzling that impact seizures are still listed as a modifying factor, as a study (9) published simultaneously with the Zurich consensus statement catagorically states that "the literature does not suppport the inclusion of impact seizures as a concussion modifer." |
| Temporal |
Frequency - repeated concussions over time (as discussed in the accompanying literature review (9) @ Table 2, citing studies @ notes 31,103, 34, 17, and 12, "in general, athletes with a previous history of concussion are more likely to present a longer duration of symptoms and are withdrawn from competition for longer following their injury. Note, however, that multiple concussion history was not predictive of concussion symptoms lasting more than 28 days in a 2013 study (7).) Timing - injuries close together in time "Recency" - recent concussion or traumatic brain injury (TBI) (Note: timing and recency continue to be included in the list of modifying factors despite the finding in the accompanying literature review (9) that there is "limited evidence to suggest that the timing or 'recency' makes any difference to timeframe of recovery following a concussion.") |
| Threshold | Repeated concussions occurring with progressively less impact force or slower recovery after each successive concussion (Note, once again, the literature review (9) accompanying the Zurich statement concludes that the evidence to suggest longer timeframes of recovery for each subsequent concussion is "limited.") |
| Age | Children and adolescents (less than 18 years old). "Recovery from concussion in children generally takes longer than that in adults. This is evident in time taken for symptom resolution, as well as neurocognitive recovery." (9) (Note, however, that two 2013 studies (6,7) did not find age to be predictive of symptoms lasting more than a week or more than 28 days, respectively.) |
| Co- and pre-morbidities |
Migraine, depression or other mental health disorders, attention deficit hyperactivity disorder (ADHD), learning disabilities, sleep disorders |
| Medication | Psychoactive drugs, anticoagulants |
| Behavior | Dangerous/more aggressive style of play (may be one reason athletes suffer recurrent concussions (5)) |
| Sport | High risk activity, contact and collision sport, high competitive level |
The presence of any of these modifying factors at the time of injury, says the Zurich consensus statement, should alert the treating practitioner to the possibility that the recovery period will be longer than the 7 to 10 day period typical of the majority (80-90%) of concussions, or that the concussed athlete may have a poorer long-term prognosis, although, as the discussion above demonstrates, there are no hard-and-fast rules and concussion management continues to be largely a matter of clinical judgment based on individual assessment.
Because of the different physiological response and longer recovery after concussion and specific risks related to head injuries during childhood and adolescence, these modifying factors likely apply even more to kids than adults and may mandate more cautious return to play advice, the Zurich statement says.
Two 2013 studies (6,7), however, found that neither age nor LOC was a risk factor for concussion symptoms lasting more than a week and 28 days respectively, and reported different findings on amnesia as a risk factor, the first finding amnesia to be associated with concussive symptoms ≥1 week only in males, but not females, and the second finding no link between amnesia and concussive symptoms lasting more than a month.
The two studies likewise reported inconsistent findings regarding multiple concussion history as a risk factor: the first finding that it doubled the risk for concussive symptoms ≥1 week, but only in football players, and the second finding no link between multiple concussion history and persistent symptoms. No wonder, then, that the Zurich consensus statement is careful to qualify its findings about modifying factors, correctly acknowledging that "in some cases, the evidence for their efficacy is limited."
Is gender a modifying factor?
The consensus statement viewed gender as a possible risk factor for injury and/or influence injury severity, but did not list it as a modifying factor based on then available research, with the accompanying literature review (9) stating that the "data thus far are inconclusive, and further study is needed to understand if gender is a risk factor for concussion."
While some studies suggest that gender is a factor, the trend in the research since 2008 appears to point towards no gender-related differences in response to concussive injury.
A 2010 study in the Journal of Athletic Training (2), for instance, contradicted the finding of a 2007 study (3) that girls take much longer than boys for concussion symptoms to resolve and return to play. It found no gender difference in terms of the time it took for symptoms to clear and for high school girls and boys to return to play.
The 2010 study did show, however, that female high school athletes present with different symptoms from male athletes, and because they are more likely to report drowsiness (a neurobehavioral symptom) and sensitivity to noise (a somatic symptom) than males - symptoms which may be more easily missed on a sideline or initial assessment or attributed to other underlying conditions, such as stress, depression, or anxiety - the authors of the study, including Dawn Comstock, who was one of the authors of the 2007 study, recommend that, where such symptoms are reported, they be viewed as symptoms of concussion until pre-existing neurobehavioral conditions are ruled out on more detailed examination.
More recently, a 2012 study (4) found no statistically significant differences between tightly matched, homogeneous groups of concussed male and female high school soccer players, either in terms of symptom score reported at baseline or in the first week after concussive injury, or in terms of postconcussion computerized neurocogntive test scores, with the only significant difference between baseline-to-postconcusson being in the total number of symptoms reported.
While the authors of the 2012 study recognized that the "results of this study could well be interpreted to indicate that there is no gender-based difference in acute response to concussive injury in high school athletes," either in terms of symptoms or neurocognitive scores, they neverless viewed the results as "supportive" of the 2009 Zurich consensus statement's position - carried forward in the 2013 Zurich statement, that gender "may be a risk factor for injury and/or influence injury severity" (1), at least for athletes in soccer.
Most recently, a 2013 study (7) found that sex was not associated with with prolonged (≥28 days) symptom duration.
AAN Guidelines differ
Further complicating matters, and illustrating just how little true consensus there is in the evaluation and management of sport-related concussion, the 2013 guidelines issued by the American Academy of Neurology (AAN)(10) depart in a number of respects from the Zurich consensus statement and/or the findings of recent studies. The AAN concludes that:
- there is a "high likelihood" that history of concussion is associated with more severe/longer duration of symptoms and cognitive deficits;
- "probable" risk factors for persistent neurocognitive problems or prolonged return to play include:
- early posttraumatic headache (not listed as a risk factor in either Zurich statement (1) or the two 2013 studies (6,7), which is not surprising, since headache is a symptom reported by virtually all (90-95%) of athletes, the vast majority of whom report being symptom free within a month)
- fatigue/fogginess:
- early amnesia (modifying factor under Zurich statement (1), not found to be risk factor for symptoms lasting ≥1 week (6) or ≥1 month (7); and
- younger age/level of play (modifying factor under Zurich (1), but not in either of the two 2013 studies (6,7)
- "possible" risk factors for more prolonged RTP include dizziness (not considered risk factors under Zurich or the 2013 studies, but viewed as one in a 2011 study (8))
- the evidence as to whether female or male sex was a risk factor was (as noted above) "conflicting," so "no conclusion could be drawn."
1. McCrory P, Consensus Statement on Concussion in Sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012. Br J Sports Med 2013: 47:250-258.
2. Frommer L, Gurka K, Cross K, Ingersoll C, Comstock R.D., Saliba S. Sex Differences in Concussion Symptoms of High School Athletes. J Ath Train 2011; 46(1):000-000.
3. Gessel LM, Fields SK, Collins CL, Dick RW, Comstock RD. Concussions among United States high school and collegiate athletes. J Ath Train 2007;42:495-503.
4. Zuckerman SL, Solomon GS, Forbes JA, Haase RF, Sills AK, Lovell MR. Response to acute concussive injury in soccer players: is gender a modifying factor? J Neurosurg: Pediatrics 2012; DOI:10.3171/2012.8.PEDS12139 (published online ahead of print October 2, 2012)(accessed October 15, 2012)
5. McCrory P, Johnston KM, Mohtadi NG, Meeuwisse W. Evidence-based review of sport-related concussion: basic science. Clin J Sport Med 2001;11:160-165.
6. Chrisman SP, Rivara FP, Schiff MA, Zhou C, Comstock R.D. Risk factors for concussive symptoms 1 week or longer in high school athletes. Brain Injury 2013;27(1):1-9.
7. Meehan W, Mannix R, Straccoilini A, Elbin R, Collins M. Symptom Severity Predicts Prolonged Recovery after Sport-Related Concussion, But Age and Amnesia Do Not. J Pediatrics 2013;
8. Lau BC, Kontos AP, Collins MW, Mucha A, Lovell MR. Which On-Field Signs/Symptoms Predict Protracted Recovery From Sport-Related Concussion Among High School Football Players? Am J. Sports Med 2011;20(10) DOI:10.1177/0363546511410655 (published June 28, 2011 online ahead of print)(accessed November 5, 2011).
9. Makdissi M, Gavis G, Jordan B, et al. Revisiting the modifiers: how should the evaluation and management of acute concussions differ in specific groups? Br J Sports Med 2013;47:314-320.
10. Giza C, Kutcher J, Ashwal S, et al. Summary of evidence-based guideline update: Evaluation and management of concussion in sports: Report of the Guideline Development Subcommittee of the American Academy of Neurologists. Neurology 2013;DOI:10.1212/WNL.0b013e31828d57dd (published online ahead of print March 18, 2013).
Most recently revised and updated May 6, 2013
