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Number and Type of Symptoms Linked To Prolonged Concussion Recovery, Study Says

Four or more symptoms, drowsiness, nausea, and concentration difficulties all associated with symptoms lasting 1 week or more

High school athletes reporting four or more symptoms of concussion at the time of injury are twice as likely to experience symptoms lasting a week or more, says a 2013 study. (1)

The study also identified links between:

  • drowsiness, nausea and concentration difficulties and prolonged symptoms; 
  • an increased risk of lingering symptoms for football players with a multiple concussion history; Concussion symptom scale
  • sensitivity to light and noise and prolonged concussion symptoms for non-football athletes; and 
  • amnesia and concussive symptoms lasting a week or more for boys, but not girls. 

Neither age nor loss of consciousness was found to be a risk factor for prolonged symptoms. 

Detailed findings 

Researchers, led by Sarah P.D. Chrisman, an adolescent medicine fellow in the Division of Adolescent Medicine at the University of Washington in Seattle, reviewed 1412 concussions in the RIOTM high school sports injury database for the period from the fall of 2006 through the spring of 2009.  

They found that: 

  • The majority of athletes (60.8%) reported four or more symptoms at the time of injury. Very few athletes reported only one symptom (4.8%)
  • Headache was the most common symptom (95.6%), followed by dizziness (79.0%), and concentration difficulties (56.1%).  Amnesia was uncommon (23.4%) and loss of consciousness (LOC) was rare (5.2%). 
  • Nausea was associated with a 60% greater risk for concussive symptoms ≥1 week in football players and an 80% greater risk for concussive symptoms in non-football players.
  • Concentration difficulties alone were linked to a 2.3-fold increase in risk for concussive symptoms ≥1 week in football players and both confusion and concentration difficulties coupled with confusion doubled the risk for lingering concussive symptoms in non-football players compared to those with neither symptoms.
  • Sensitivity to light and noise put non-football players at 2.7-fold greater risk of concussive symptoms  ≥1 week in non-football players, but was not significant for football players.
  • Amnesia was associated with an 80% greater risk for concussive symptoms ≥1 week for non-football playing males, but was not significant for females. 

Help in RTP guidelines

"This analysis of the RIOTM  database indicates that risk factors for concussive symptoms ≥1 are identifiable and will be useful for the design of future evidence-based [return to play] guidelines, as well as for prognostication with athletes and families regarding concussion severity" and the likelihood of return-to-play at 1 week," wrote Chrisman.

She noted that, while LOC was historically thought to be a marker for concussion severity, so that it was used in concussion grading scales (now abandoned) as a way of stratifying risk, the results in the study were consistent with those finding no association between LOC and severity, although Chrisman recognitzes that LOC ≥1 minute (which the 4th International Consensus Statement on Concusson in Sport (2) continues to list as a potential "modifying" factor suggesting a longer recovery/more severe concussion) deserves additional research as a risk factor."  

Study limitations

"This data was collected by athletic trainers, as much of the data in the literature has been to this point," said Chrisman. "While this is a very useful method of collecting data (and inexpensive, since someone is already paying them), it can create bias since athletic trainers spend more time on the sideline of football than they do covering other sports. As a result, concussions that occur in football are more likely to be captured. Those that occur in other sports have to be more severe to come to the athletic trainer's attention. This is why we analyzed football players separately from non-football players: because we felt the methods of recognizing the injuries were so different for non-football sports, and therefore these populations should not be combined. It also allowed us to compare women and men. Since women can't play football, it was an unfair comparison to assess the effect of sex when football players were included." 

"Measurement of injury progression is inherently difficult. However we did not use self-report of symptoms-these athletes were being assessed by an athletic trainer. Regardless, there may be some problems with using symptoms to follow the progression of concussive injury, but there are difficulties with other methods as well. Repetitive neurocognitive testing can be associated with a learning effect which makes it difficult to assess whether athletes are actually improving or only learning the test. In addition, these tests may not measure all aspects of injury. For example, the ImPACT test does not measure complex frontal processing, or "executive functioning," which is often impaired in concussed athletes. Most clinicians can recall athletes that "pass" these neurocognitive tests, but who clinically still show signs and symptoms of injury. Functional MRI is also not a perfect measure. Although athletes might show changes on FMRI for weeks or months, we don't understand what these changes mean and they might represent healing, not continued injury," said Chrisman.

Chrisman agreed that the role of gender in concussion is confusing. "This study addressed gender in a more balanced way than has been done previously and we did not find it played a large role. We are currently designing to studies to examine rotational and linear forces in males vs. females, and we hope these studies will more definitively answer some of the questions regarding gender." 

Evidence-based RTP guidelines still long way off 

"I think we have a long way to go towards developing evidence-based return to play guidelines, but this is a first step," said Chrisman. "With these data we can ask clinicians to be more wary with certain athletes (for example, those who present with multiple symptoms, or who are drowsy and nauseous). Clinicians can warn the athletes they may need to be out longer. My hope is that with additional studies we can begin to develop stratified risk profiles, as we use in the emergency room, so that we do not miss the very severely injured athletes who need our attention."   

1. 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. 

2.  McCory P, et al. 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.

3. 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; DOI 10.1016/j.jpeds.2013.03.012 (published online ahead of print April 25, 2013).