Journal of Clinical and Experimental Neuropsychology, 2015 Vol. 37, No. 3, 265–275, http://dx.doi.org/10.1080/13803395.2015.1004303

Injury-related predictors of symptom severity following sports-related concussion Victoria C. Merritt1, Amanda R. Rabinowitz2, and Peter A. Arnett1 1 2

Department of Psychology, Pennsylvania State University, University Park, PA, USA Department of Neurosurgery, University of Pennsylvania School of Medicine, Philadelphia, PA, USA

(Received 18 August 2014; accepted 31 December 2014) Introduction: Decisions regarding return to play after sports-related concussion partially revolve around athletes’ self-reported symptoms. Given this emphasis on symptoms, it would be beneficial to be able to identify characteristics that could predict which athletes may be susceptible to developing an increase in postconcussion symptoms following head injury. The purpose of this study was to describe the symptoms that athletes endorse immediately following concussion and to determine what impact injury-related characteristics have on the development of postconcussion symptoms within the first week following concussion. Method: Participants included 54 collegiate athletes who sustained concussions and were referred to our concussion management program for postconcussion testing. The main outcome measures included the Post-Concussion Symptom Scale and an interview querying athletes’ retrospective symptoms over time, starting immediately postinjury. Results: Descriptive statistics revealed that the most common immediate symptoms following concussion include dizziness (endorsed by 83.6% of the sample), headache (65.5%), feeling in a fog (61.8%), and visual disturbance (60.0%). Logistic regression analyses indicated that retrograde and anterograde amnesia, as well as loss of consciousness, were not significantly predictive of postconcussion symptoms within one week following concussion (p > .05). However, the total symptom score assessed immediately postinjury, in addition to endorsing immediate headache symptoms following concussion, reliably predicted a higher level of symptom reporting in the first week following concussion (p < .05). Finally, receiver-operating characteristic (ROC) curve analysis, using 80% sensitivity to predict the high postconcussion symptom group, established cutoff scores of 7.5 for the immediate total symptom score and 0.5 for immediate headache. Conclusions: These findings demonstrate the importance of evaluating symptoms immediately following concussion. Athletes who endorse more immediate postconcussion symptoms, especially headache symptoms, may be at risk for greater and more severe postconcussion symptoms within the first week following concussion. The present findings have implications for the management and treatment of sports-related concussions. Keywords: Concussion; Headache; Symptom reporting; Sports injuries; Mild traumatic brain injury.

The management and treatment of sports-related concussions have garnered widespread attention from a variety of disciplines over the past several decades. Some of the major areas of interest within this domain have been developing better diagnostic and classification criteria for concussion, better

understanding the role and/or significance of traditional markers of injury severity such as loss of consciousness and amnesia, and developing appropriate guidelines for return to play (McCrory et al., 2013). Although some advances have been made with respect to concussion management and

We would like to thank Dr. Wayne Sebastianelli and Penn State Sports Medicine for their generous support of our research. Also, the authors would like to thank Gray Vargas, Fiona Barwick, Aaron Rosenbaum, and Chris Bailey for their help as project coordinators of the program over the years. Finally, a special thanks to the following individuals for their help with running participants and data entry for this project: Karissa Arthur, Dan Brynien, Saima Farooq, Caitlin Gaffney, Alex Garrison, Briana Hauser, Mark Petusky, Matt Phillips, Jordyn Sessel, Julie Turco, and Steven Yacovelli. Address correspondence to: Victoria C. Merritt, Department of Psychology, Penn State University, 372 Moore Building, University Park, PA 16802, USA (E-mail: [email protected]).

© 2015 Taylor & Francis

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treatment in recent years, there remains little consensus regarding the proper procedures to follow once athletes sustain concussions, and how best to determine when athletes are ready to return to play. The most recent recommendation put forth by the 4th International Conference on Concussion in Sport proposes that athletes should rest—physically and cognitively—following concussion, and they should not begin the return to play protocol until postconcussion symptoms have resolved (McCrory et al., 2013). These recommendations are based on the assumption that elevated symptom reports suggest ongoing neurological dysfunction and increased vulnerability for additional injury or symptom exacerbation. Given the current emphasis on symptoms, a beneficial next step would be to identify characteristics that could predict which athletes may be susceptible to developing an increase in postconcussion symptoms following head injury. Identifying individuals at greatest risk of increased symptom reporting following concussion is the first step towards developing interventions that might aid in recovery and may lead to the development of more targeted interventions for those individuals who are most likely to benefit. To date, relatively few studies have examined such predictors of postconcussion symptoms. Among those that have, Collins et al. (2003) reported increased risk of symptoms and neurocognitive deficits related to posttraumatic amnesia (PTA), and Lau, Lovell, Collins, and Pardini (2009) reported that migraine-related symptoms and neurocognitive performance, when assessed, on average, two days postconcussion, were predictive of prolonged recovery following concussion. Recently, McCrea and colleagues (2013) reported that loss of consciousness (LOC), PTA, and symptom severity within one day of injury predicted longer recovery time. LOC, however, has not been consistently related to prolonged symptoms, with some studies finding an association between LOC and prolonged recovery (McCrea et al., 2013) and others finding no such association (Lau et al., 2009). Other work suggests that the presence of specific symptom profiles may confer risk for prolonged dysfunction. Lau, Kontos, Collins, Mucha, and Lovell (2011), for example, reported that dizziness at the time of injury was the only variable that predicted protracted recovery. Finally, Makdissi and colleagues (2010) found that prolonged headache (lasting 60 hours or more), as well as symptoms of “fatigue/fogginess” and the presence of four or more immediate symptoms were associated with taking a longer time to return to play. Given the limited research that has examined early predictors of postconcussion symptoms, as

well as the disparate nature of the existing literature, the present study sought to explore the relationship between early predictors and the development of symptoms within the acute injury period following concussion. A variety of early predictors were examined, including traditional injury-severity predictors, as well as several immediate symptom variables (assessed retrospectively). It was hypothesized that both retrograde and anterograde amnesia, but not LOC, would be predictive of a high symptom score within one week following concussion. As for the other variables, the examination of these relationships was exploratory in nature, and no specific hypotheses were generated. An additional goal of the study was to describe the type and severity of symptoms that athletes endorse immediately following sports-related concussion and to document the most common immediate symptoms that result from concussion. To date, several studies have documented common symptoms that occur within two to seven days following concussion and beyond, but very few studies have examined immediate symptoms following concussion. However, according to an earlier study by Guskiewicz, Weaver, Padua, and Garrett (2000), headache, dizziness, and confusion were the most common immediate postconcussion symptoms reported in their sample of football players. Therefore, it was hypothesized that these symptoms would be comparably prevalent in our broader sample of college athletes.

METHOD Participants Participants included 54 collegiate athletes who were involved in a concussion management program. Athletes participating in the program were assessed via neurocognitive and neurobehavioral measures prior to and following sports-related concussion. Participants analyzed in the present study were selected from a larger sample of 80 concussed athletes. Exclusion criteria included the following: (a) The concussion did not result from participation in a sports-related event (n = 10); (b) postconcussion testing occurred more than one week postinjury (n = 15); and (c) participants failed to complete the postconcussion interview (n = 1). The one-week time interval was chosen so as to remain within the expected period of probable impairment following concussion (Echemendia, Putukian, Mackin, Julian, & Shoss, 2001; Iverson, Brooks, Collins, & Lovell, 2006; McCrea et al., 2013).

INJURY-RELATED PREDICTORS OF SYMPTOMS TABLE 1 Athlete characteristics Variable

Number

%

Gender Male Female

46 8

85.2 14.8

Ethnicity Caucasian African American Other

31 17 6

57.4 31.5 11.1

Concussion history 0 1 2 or more

27 16 11

50.0 29.6 20.4

Sport Football Men’s basketball Men’s ice hockey Men’s lacrosse Men’s soccer Women’s basketball Women’s lacrosse Women’s soccer

27 5 2 10 2 1 3 4

50.0 9.3 3.7 18.5 3.7 1.9 5.5 7.4

Note. N = 54.

Thus, the final sample consisted of 54 male and female athletes (age at concussion: M = 19.89 years, SD = 1.41), and the average time tested postinjury was 62 hours (3 days; SD = 32.92). Additional sample characteristics are presented in Table 1.

Procedure Athletes were referred for postconcussion testing by an athletic trainer or team physician if they experienced a concussion (i.e., mild traumatic brain injury), defined as experiencing loss of consciousness (30 minutes or less), retrograde or anterograde amnesia surrounding the concussion (anterograde amnesia not lasting longer than 24 hours), or any alteration in mental status at the time of injury (Ruff, Iverson, Barth, Bush, & Broshek, 2009). Testing included administration of a neuropsychological test battery, as well as a postconcussion interview. The neuropsychological measures were administered by graduate students and undergraduate research assistants, under the supervision of a PhD-level clinical neuropsychologist, and the postconcussion interview was administered by a PhDlevel clinical neuropsychologist or the Concussion Program Coordinator, a trained doctoral student in clinical psychology specializing in neuropsychology. The testing sessions took approximately two

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hours to complete. The university’s Institutional Review Board approved the study, and all athletes underwent an informed consent process prior to participation. Measures The main outcome measure for this study was the Post-Concussion Symptom Scale (PCSS), assessed in our sample during that first week postconcussion. The PCSS is administered via computer through the ImPACT program (Lovell, Collins, Podell, Powell, & Maroon, 2000). The measure consists of 22 symptoms that are evaluated on a 7-point scale ranging from 0 to 6 (with 0 indicating no symptoms and 6 indicating severe symptoms), and athletes are asked to rate the extent to which they are currently experiencing each symptom. The PCSS is reported to have an internal consistency of .89–.94 (Lovell et al., 2006), and Cronbach’s alpha for the current study was .94. Additionally, athletes were administered a postconcussion interview. The interview gathers basic demographic data and information pertaining to the nature of the concussive injury, such as how the injury occurred, whether the athlete lost consciousness and/or experienced retrograde or anterograde amnesia, and a retrospective report of symptoms beginning immediately following the injury. Ten common symptoms are included in the interview: disorientation, nausea, dizziness, balance problems, visual disturbance, numbness/tingling, feeling in a fog, pressure in head, problems with attention, and headache. Athletes are asked to retrospectively rate their immediate postconcussion symptoms on a scale of 0–6, where 0 is no symptoms, and 6 is severe symptoms. Retrospective ratings of symptoms were utilized because athlete symptom reports at the time of injury were not available. Although immediate reports at the time of injury would be ideal, there is a precedent within the sports concussion literature of utilizing retrospective symptom reporting as a reliable and valid method for predicting postinjury outcome (Llewellyn, Burdette, Joyner, & Buckley, 2014; McNally et al., 2013; Yeates et al., 2009). In the present study Cronbach’s alpha for the postconcussion interview symptom score was .84. Approach to data analysis To describe the nature of athletes’ symptom reporting immediately following concussion, descriptive statistics were run on the 10 symptoms that are included in the postconcussion interview.

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Next, separate logistic regression analyses (King, 2008; Peng, Lee, & Ingersoll, 2002) were conducted to assess the extent to which the following early predictors contributed to the postconcussion PCSS total score assessed during the first week postconcussion (hereafter referred to as “total symptom score”):

● Analysis 1: Traditional markers of injury severity as predictors of total symptom score during first week postinjury. Predictor variables included LOC, retrograde amnesia, and anterograde amnesia. For the purpose of the logistic regression analyses, all three variables were dichotomized (i.e., yes or no). ● Analysis 2: Immediate aggregate symptom scores as predictors of total symptom score during first week postinjury. ● Analysis 2a: The total immediate symptom score (based on the postconcussion interview) was the sole predictor variable. The total immediate symptom score for each athlete was determined by adding together individual responses to all 10 symptoms. This variable was entered into the logistic regression analysis as a continuous variable. ● Analysis 2b: The number of immediate symptoms endorsed following concussion was the sole predictor variable. This value was calculated by counting the total number of positively endorsed symptoms (i.e., adding together the number of symptoms endorsed with a severity rating of “1” or greater). This variable was entered into the logistic regression analysis as a continuous variable. ● Analysis 3: Most common immediate symptoms as predictors of total symptom score during the first week postinjury. Predictor variables included the most commonly endorsed individual symptoms immediately following concussion (based on symptoms listed within the postconcussion interview). The most commonly endorsed individual symptoms were determined by selecting those symptoms that were endorsed by 60% or more of the sample at any severity rating. The most common immediate symptoms were entered into the regression analysis as dichotomous variables (i.e., yes or no).

TABLE 2 Demographic data for “low symptoms” and “high symptoms” groups postconcussion Group Low symptoms (N = 17)

High symptoms (N = 37)

Age (years) Education (years)

19.59 (1.28) 13.12 (1.41)

20.03 (1.46) 13.46 (1.35)

Gender Male Female

16 1

30 7

Concussion history 0 1 2 or more

7 4 6

20 12 5

Sport Football Men’s basketball Men’s ice hockey Men’s lacrosse Men’s soccer Women’s basketball Women’s lacrosse Women’s soccer

8 0 2 4 2 0 0 1

19 5 0 6 0 1 3 3

Variable

Note. N = 54.

total score. Given the positive skew of the baseline PCSS data, the median (as opposed to the mean) was thought to provide a more accurate representation of low versus high symptoms postconcussion. The median for the baseline PCSS data was 2. Those having PCSS total scores falling at or below the median (i.e., at or below 2) were included in the “low symptoms” group, and those with scores falling above the median (>2) were included in the “high symptoms” group. Additional descriptive characteristics pertaining to these two groups are provided in Table 2. Finally, after conducting the logistic regression analyses, we used receiver-operating characteristic (ROC) curve analyses to determine specific cutoff scores for any of the significant predictor variables found in the logistic regression analyses. All analyses were conducted with the Statistical Package for the Social Sciences (SPSS), Version 19.0, and significance levels were set at p < .05.

RESULTS Descriptive statistics

Binary logistic regression was used to predict the total symptom score as a categorical outcome variable. The total symptom score was categorized into either a “low symptoms” or a “high symptoms” group based on a median split of the baseline PCSS

Fifty-four athletes sustained concussions and subsequently completed the postconcussion interview and the PCSS. However, one participant did not have symptom data from the postconcussion

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TABLE 3 Descriptive statistics for immediate postconcussion symptoms Symptom Dizziness Headache Feeling in a fog Visual disturbance Disorientation Balance problems Pressure in the head Attention Nausea Numbness

Mean

SD

Min

Max

Skewness

Kurtosis

2.68 2.62 2.19 2.26 2.04 1.80 1.94 1.77 0.68 0.75

1.72 2.31 2.19 2.26 2.15 2.04 2.12 2.11 1.44 1.79

0 0 0 0 0 0 0 0 0 0

6 6 6 6 6 6 6 6 6 6

0.07 0.11 0.58 0.42 0.57 0.68 0.55 0.71 2.13 2.28

–0.80 –1.62 –1.03 –1.37 –1.12 –1.02 –1.13 –0.96 3.70 3.75

Note. N = 53.

interview and was therefore not included in the present analyses. Descriptive statistics for immediate postconcussion symptoms (based only on those symptoms included in the postconcussion interview) are presented in Table 3, and Figure 1 displays the frequency of immediate postconcussion symptoms. Dizziness was the most common immediate symptom (endorsed by 83.6% of the sample), followed by headache (65.5%), feeling in a fog (61.8%), and visual disturbance (60.0%). The least common immediate symptoms following concussion included nausea (endorsed by 21.8% of the sample) and numbness/tingling (18.2%). The mean total score of immediate postconcussion symptoms (possible range of 0–60) for the sample was 18.7

(SD = 12.9), and the observed range was 0–48. With respect to the number of positively endorsed symptoms (possible range of 0–10), the mean for the sample was 5.4 (SD = 2.6), the median was 6.0, and the observed range was 0–10. Finally, Table 4 contains information pertaining to the severity of immediate postconcussion symptoms. The most common “severely” rated symptom, defined as a rating of 5 or 6 on the postconcussion interview, was headache, which was endorsed by 15 athletes (or 28.3% of the sample). Other common “severely” rated symptoms included visual disturbance (endorsed by 11 athletes, or 20.8% of the sample) and feeling in a fog (endorsed by 10 athletes, or 18.9% of the sample).

Figure 1. Frequency of postconcussion symptoms immediately following concussion (N = 53).

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symptom score as the dependent variable; see Table 5).

TABLE 4 Number of athletes endorsing postconcussion symptoms, based on symptom severity, immediately following concussion Symptom severitya Symptom

0

1

2

3

4

5

6

Dizziness Headache Feeling in a fog Visual disturbance Disorientation Balance problems Pressure in the head Attention Nausea Numbness

7 17 19 20 22 24 25 27 41 43

8 6 6 6 4 6 1 3 2 1

8 3 6 4 7 4 5 2 3 3

13 3 8 4 4 4 8 8 2 0

9 9 4 8 7 8 6 6 4 0

5 8 2 4 4 4 4 3 0 3

3 7 8 7 5 3 4 4 1 3

Analysis 2: Immediate aggregate symptom scores as predictors of total symptom score during first week postinjury Analysis 2a. Binary logistic regression was used to examine whether the immediate total symptom score could identify athletes with low or high postconcussion symptoms within the first week following concussion. The immediate total symptom score was a significant predictor of postconcussion symptom group (i.e., low or high postconcussion symptoms), χ2(1, N = 53) = 4.01, p < .05, and accounted for 10% of the variance. However, classification results indicated that just 5.9% of the athletes with low symptoms were correctly classified, whereas 91.7% of the athletes with high symptoms were correctly classified, with the model correctly predicting 64.2% of the cases (see Table 5).

Note. N = 53. a The severity of symptoms is based on a 0–6 scale, with 0 indicating no symptoms and 6 indicating severe symptoms.

Regression analyses Analysis 1: Traditional markers of injury severity as predictors of total symptom score during first week postinjury

Analysis 2b. Binary logistic regression was also used to examine whether the total number of immediate symptoms endorsed following concussion could identify athletes with low or high symptoms within one week following concussion. The total number of immediate symptoms was not a significant predictor of postconcussion symptom group, χ2(1, N = 53) = 2.61, p = .11, indicating that this particular measure of immediate symptom reporting does not reliably distinguish between athletes with low and high postconcussion

Using binary logistic regression, a test of the full model with the three predictor variables (LOC, and retrograde and anterograde amnesia) against a constant-only model was not statistically significant, χ2(3, N = 54) = 3.47, p = .32, indicating that the predictors, as a set, do not reliably distinguish between athletes with low and high postconcussion symptoms (based on the total

TABLE 5 Logistic regression for injury-specific characteristics predicting dichotomized postconcussion PCSS scores

Analysis

Predictor variable

β

SE β

Wald’s χ2 (df = 1)

p

eβ (odds ratio)

Analysis 1

Constant LOCa Retrograde amnesiaa Anterograde amnesiaa

1.36 0.04 1.69 –0.83

0.60 0.78 1.16 0.68

5.19 0.00 2.11 1.52

.02 .96 .15 .22

3.90 1.04 5.41 0.44

Analysis 2a

Constant Total immediate symptom scoreb

–0.11 0.05

0.52 0.03

0.04 3.56

.84 .06

0.90 1.05

Analysis 2b

Constant Number of immediate symptomsb

–0.20 0.18

0.65 0.12

0.09 2.51

.76 .11

0.82 1.20

Analysis 3

Constant Dizzinessa Headachea Feeling in a foga Visual disturbancea

1.02 –1.25 2.47 0.05 –0.91

0.52 1.17 0.86 0.79 0.80

3.94 1.14 8.33 0.00 1.23

.05 .29 .00 .96 .26

2.78 0.29 11.79 1.05 0.40

Note. PCSS = Post-Concussion Symptom Scale; LOC = loss of consciousness. Variable entered into regression analysis as a dichotomous variable (i.e., yes or no). bVariable entered into regression analysis as a continuous variable. a

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symptoms within one week following concussion (see Table 5).

Analysis 3: Most common immediate symptoms as predictors of total symptom score during the first week postinjury Using binary logistic regression, a test of the full model with the four predictor variables (dizziness, headache, feeling in a fog, and visual disturbance reported immediately following concussion) against a constant-only model was statistically significant, χ2(4, N = 53) = 11.04, p = .03, indicating that the most commonly endorsed immediate postconcussion symptoms, as a set, reliably distinguished between athletes with low and high postconcussion symptoms within the first week following concussion (Nagelkerke’s R2 = .26). Classification results indicated that 52.9% of the athletes with low symptoms were correctly classified, and 86.1% of the athletes with high symptoms were correctly classified, with the model correctly predicting 75.5% of the cases. According to the Wald criterion, headache was the only immediate symptom that made a significant contribution to the prediction of symptom group (Table 5). Examination of the odds ratios suggests that an athlete who endorses headache symptoms immediately following a concussion is 11.5 times more likely to fall within the high symptom group within a week following the injury than athletes who do not report headache immediately following a concussion.

ROC curve analysis Given that the immediate total symptom score and immediate headache were the only significant predictor variables in the above analyses, these were the only two variables that were examined as predictors in the ROC curve analysis. ROC curve analysis (see Figure 2) showed that both variables (immediate total symptom score and immediate headache) were significant at predicting postconcussion symptom group (immediate total symptom score: area under curve, AUC = .63, p < .05, 95% confidence interval, CI [.53, .82]; headache: AUC = .72, p = .01, 95% CI = [.57, .87]). Using 80% sensitivity for detecting those who would fall in the high symptoms group, a cutoff score of 7.5 was established for the immediate total symptom score (specificity = 41.2%, positive predictive value = 70.8%), and a cutoff score of 0.5 was established for immediate headache (specificity = 58.8%, positive predictive value = 77.6%).

Figure 2. Receiver-operating characteristic (ROC) curve of immediate total symptom score and immediate headache following concussion.

DISCUSSION The purpose of the present study was twofold. First, this investigation was designed to describe the type and severity of symptoms that athletes endorse immediately following sports-related concussion. Our results suggest that dizziness, headache, feeling in a fog, and visual disturbance are the most common immediate symptoms endorsed by concussed athletes (in order of frequency), and that headache, visual disturbance, and feeling in a fog are the most severely rated immediate symptoms. Although several studies have reported on common postconcussion symptoms, many of these studies have focused on symptom reports that are gathered at the time of the athletes’ postconcussion testing session, which usually takes place within 1–2 weeks following the injury, or at monthly (i. e., 1-, 3-, or 6-month) or yearly follow-up appointments (Covassin, Schatz, & Swanik, 2007; Frommer et al., 2011; Kontos et al., 2012; Lovell et al., 2006; Ponsford et al., 2012). Few studies, however, have reported on the nature of athletes’ symptom-reporting patterns immediately following concussion. Makdissi et al. (2010) examined clinical features that were reported at the time of injury in a sample of football players, and they found that headache was the most common symptom (endorsed by 87.5% of the sample), followed by confusion/disorientation (62.5%) and visual disturbance (40.9%). An older study by Erlanger et al. (2003) also found that headache was the most common immediate postconcussion symptom

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(endorsed by 93.6% of the sample), followed by dizziness (85.1%) and confusion/disorientation (83.0%). Similarly, Guskiewicz et al. (2000) reported an identical pattern of symptoms, but with slightly lower rates than those in the Erlanger et al. (2003) study. The present results are generally consistent with these studies with respect to the types of symptoms that are commonly endorsed at the time of injury; however, the relative occurrence of each symptom varies among studies, perhaps due to sample differences. In addition to describing immediate postconcussion symptoms, we sought to explore the relationship between traditional markers of injury severity and the development of symptoms within one week following concussion. We hypothesized that the presence of retrograde and anterograde amnesia, but not LOC, would be predictive of the high symptoms group within the acute injury period following concussion, but the results did not support this hypothesis. Specifically, all three traditional injury severity markers (i.e., retrograde and anterograde amnesia and LOC) were not found to be associated with postconcussion symptom reporting. The present results are consistent with many studies that have shown that these variables are not predictive of postconcussion symptom reporting or prolonged recovery following concussion (Lau et al., 2011; Lau et al., 2009; Makdissi et al., 2010; Meehan, Mannix, Stracciolini, Elbin, & Collins, 2013; Ponsford et al., 2012). Still, a few studies have shown that such variables are predictive of postconcussion symptom reporting (Collins et al., 2003) and prolonged recovery (McCrea et al., 2013), indicating that further examination of these variables may be warranted. Nevertheless, our findings join a growing number of studies reporting that LOC and retrograde and anterograde amnesia surrounding the injury event are not predictive of postconcussion symptoms or prolonged recovery. This raises questions about the reliability and validity of these traditional injury severity makers of concussion. Although determining the value of traditional markers of injury severity goes beyond the scope of the current paper, mounting evidence suggests that current tools fail to adequately explain the heterogeneity in concussion outcomes. The field is in need of valid biomarkers of concussion-related neuropathology. Advanced neuroimaging methods (Bazarian et al., 2007; Inglese et al., 2005; Wilde et al., 2008) and blood serum proteins (Siman et al., 2013) are promising candidates in this regard; however, more research is needed to establish the diagnostic and prognostic utility of these measures.

Next, with respect to the symptom-related variables (i.e., total immediate symptom score, total number of immediate symptoms endorsed, and the most commonly reported individual symptoms), the total immediate symptom score and headache were the only variables that were found to reliably predict athletes’ postconcussion symptom group (low vs. high total symptom score). Specifically, the regression results showed that the immediate total symptom score reliably predicted whether an athlete would endorse high or low symptoms within one week of sustaining a concussion, such that a higher immediate total symptom score was associated with being more likely to fall within the high symptoms group postconcussion. However, the amount of variance explained was only 10%. On the other hand, the regression results showed that an athlete who endorses headache symptoms immediately following a concussion is 11.5 times more likely to fall within the high symptom group within a week following the injury than athletes who do not report headache immediately following a concussion. The amount of variance explained by immediate headache alone was 26%, potentially representing a more clinically meaningful result. Although this appears to be a unique finding, the results are somewhat consistent with Makdissi et al.’s (2010) report that prolonged headache (i.e., headache lasting at least 60 hours) is associated with taking a longer time to return to play. Furthermore, other studies (Kontos et al., 2013; Mihalik et al., 2013; Mihalik et al., 2005) have examined migraine symptoms as predictors of prolonged recovery following concussion and have reported an association between immediate migraine symptoms and protracted recovery and/ or prolonged symptom recovery. Finally, with respect to the ROC curve analysis, area under the curve results support the results of the logistic regression analyses, indicating that both the total immediate symptom score and immediate headache were significant predictors of postconcussion symptom group. More importantly, though, specific cutoff scores (using 80% sensitivity) were established for each of these variables. With respect to the immediate total symptom score, having a total score of 7.5 or greater likely differentiates between athletes who will fall in the high versus low symptoms group within one week following concussion. As for immediate headache, endorsing headache at a severity level of 0.5 or greater best differentiates between athletes falling in the high versus low symptoms group. Moreover, the results showed that endorsement of immediate headache, at any severity level, is associated with experiencing greater postconcussion

INJURY-RELATED PREDICTORS OF SYMPTOMS

symptoms within one week of the injury. Although the specificity for both immediate total symptom score and immediate headache is low, this is less of a concern because the outcome of interest is being able to accurately predict those who might endorse high symptoms within a week following concussion. Therefore, given the sufficient sensitivity, the results are thought to be clinically meaningful.

Clinical implications A major challenge within the medical community has been developing evidence-based guidelines for the treatment and management of sports-related concussions. Presently, great emphasis is being placed on postconcussion symptoms, and return to play decisions are at least partially based on symptom resolution (McCrory et al., 2013); as such, determining risk factors for the development of postconcussion symptoms can be valuable. The finding that endorsement of immediate headache following concussion is predictive of athletes who are at risk of falling within the high symptoms group within one week following concussion has notable implications for concussed athletes. First, our results provide support for the continued use of postconcussion symptom inventories as a way to track and monitor symptom resolution following concussion. However, our findings suggest that individual symptoms (such as headache) may be more informative than summary measures such as a total symptom score. Although a vast number of studies utilize total symptom scores, examining individual immediate symptoms appears to have notable implications for determining who may be at risk for increased symptoms within a week following concussion. Finally, the finding that loss of consciousness and retrograde and anterograde amnesia were not predictive of symptom reporting within the week following concussion raises questions regarding the value of these traditional markers of injury severity in the sports-concussion population. There are currently no evidence-based treatments for prolonged concussion dysfunction and no way of predicting which athletes are at risk for more severe and complicated recovery trajectories. This causes much uncertainty and anxiety for athletes and clinicians alike. Given that the majority of concussed athletes recover completely from their injuries within days of being concussed, it is impractical to design clinical trials that include all recently concussed athletes. Early predictors are necessary for developing interventions to hasten recovery for those at risk for more lasting

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concussion symptoms. The present findings suggest that it might be beneficial to develop individually targeted treatments that focus on athletes who report early-onset headache immediately following concussion. Limitations There are some limitations to this study that should be addressed. First, athletes completed the postconcussion interview when they came to our clinic for their postconcussion testing session. As a result, their report of immediate symptoms was based on retrospective recall of the symptoms they experienced at the time of injury. It is possible that, had we asked the athletes to report their symptoms immediately following the concussive hit, their reports may have differed. Nonetheless, there is some precedent within the sports concussion literature of utilizing retrospective symptom reporting as a reliable and valid method for predicting postinjury outcome (Llewellyn et al., 2014; McNally et al., 2013; Yeates et al., 2009). Additionally, using immediate symptom reports following concussion, Guskiewicz et al. (2000) and Erlanger et al. (2003) reported findings similar to ours, with both headache and dizziness being two of the most commonly reported symptoms. Second, it is conceivable that when athletes were completing the PCSS during their postconcussion appointment, they minimized their current symptoms. Previous studies have shown that athletes may minimize their impairment, including their symptom presentation, because of concerns over return to play (Bailey, Echemendia, & Arnett, 2006; Echemendia & Julian, 2001). In the present study, the main outcome variable for the regression analyses was the postconcussion PCSS total symptom score; if athletes did not accurately report their symptoms, the classification of low versus high symptom groups may be misrepresentative. Nevertheless, self-reported symptoms are a vital component for determining when to return athletes to play, and so there is merit in utilizing these symptom reports. Finally, the limited number of females included in the postconcussion sample is a shortcoming, and, as a result, the findings may not be as representative for female athletes. CONCLUSION The purpose of this study was to describe the symptoms that athletes endorse immediately following concussion and to determine what impact injuryrelated characteristics have on the development of

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postconcussion symptoms within the first week following concussion. Our findings suggest that although few injury-specific characteristics predict athletes’ symptom reporting postconcussion, paying attention to immediate symptoms that follow a concussive injury is crucial. Specifically, the most common symptoms endorsed by athletes include dizziness, headache, feeling in a fog, and visual disturbance, and athletes at risk for higher postconcussion symptom reporting include those who endorse headache symptoms at the time of injury. Our findings demonstrate the importance of evaluating symptoms immediately following concussion and indicate that athletes who endorse immediate headache may be at risk for greater and more severe postconcussion symptoms in the subsequent week following concussion. Future work addressing some of the limitations of our study will be necessary to validate our findings.

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Injury-related predictors of symptom severity following sports-related concussion.

Decisions regarding return to play after sports-related concussion partially revolve around athletes' self-reported symptoms. Given this emphasis on s...
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