The purpose of this study was to identify factors that are predictive of, or associated with, high endorsement of postconcussion and posttraumatic stress symptoms following military-related traumatic brain injury (TBI). Participants were 1,600 U.S. service members (age: M = 27.1, SD = 7.1; 95.4% male) who had sustained a mild-to-moderate TBI and who had been evaluated by the Defense and Veterans Brain Injury Center at one of six military medical centers. Twenty-two factors were examined that included demographic, injury circumstances/severity, treatment/evaluation, and psychological/physical variables. Four factors were statistically and meaningfully associated with clinically elevated postconcussion symptoms: (i) low bodily injury severity, (ii) posttraumatic stress, (iii) depression, and (iv) military operation where wounded (p < .001, 43.2% variance). The combination of depression and posttraumatic stress symptoms accounted for the vast majority of unique variance (41.5%) and were strongly associated with, and predictive of, clinically elevated postconcussion symptoms [range: odds ratios (OR) = 4.24–7.75; relative risk (RR) = 2.28–2.51]. Five factors were statistically and meaningfully associated with clinically elevated posttraumatic stress symptoms: (i) low bodily injury severity, (ii) depression, (iii) a longer time from injury to evaluation, (iv) military operation where wounded, and (v) current auditory deficits (p < .001; 65.6% variance accounted for). Depression alone accounted for the vast majority of unique variance (60.0%) and was strongly associated with, and predictive of, clinically elevated posttraumatic stress symptoms (OR = 38.78; RR = 4.63). There was a very clear, strong, and clinically meaningful association between depression, posttraumatic stress, and postconcussion symptoms in this sample. Brain injury severity, however, was not associated with symptom reporting following TBI.

Introduction

The conflicts in Iraq and Afghanistan have resulted in a dramatic rise in the incidence and prevalence of posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI), particularly mild TBI (Defense and Veterans Brain Injury Center, 2012; Tanielian & Jaycox, 2008; Veterans for Common Sense, 2012). For all clinicians within the military healthcare system, the correct identification and diagnosis of PTSD and mild TBI following deployment can be challenging, yet is a fundamental role that the healthcare system must provide to ensure the provision of high-quality clinical care. Of equal importance is the early detection of patients who might be at risk of poor outcome following mild TBI and/or exposure to traumatic events while deployed. Early detection of patients who are at risk of poor outcome can potentially result in early treatment and the opportunity to minimize the possibility of poor long-term outcome. Researchers have demonstrated that early intervention programs for civilians who have sustained mild TBIs are helpful for some (Mittenberg, Tremont, Zielinski, Fichera, & Rayls, 1996; Paniak, Toller-Lobe, Durand, & Nagy, 1998; Ponsford et al., 2002) but certainly not all people (Elgmark Andersson, Emanuelson, Bjorklund, & Stalhammar, 2007). Similarly, early intervention programs for traumatic stress have been shown to reduce the likelihood of developing PTSD (Bryant et al., 2008; Bryant, Moulds, & Nixon, 2003; Shalev et al., 2012).

Outcome following mild TBI is complicated. Without question, postconcussion symptoms are common following mild TBI. Symptoms largely resolve within the first week to 6 months postinjury in athletes, civilians, and military service members (Dischinger, Ryb, Kufera, & Auman, 2009; Lange et al., 2013; Lange, Brickell, Ivins, Vanderploeg, & French, 2013; Macciocchi, Barth, Alves, Rimel, & Jane, 1996; McCrea et al., 2003; Ponsford et al., 2000). However, a minority of people report symptoms many months or years postinjury (Bohnen et al., 1994; Deb, Lyons, & Koutzoukis, 1998; Rutherford, Merrett, & McDonald, 1979; Ryan & Warden, 2003; Wood, 2004; Youngjohn, Burrows, & Erdal, 1995). Recent research has shown that postconcussion symptom reporting many months or years postinjury does not tend to be characterized as “persistent” over time, but rather as “variable”. While a small percentage of people do report persistent symptoms from baseline to follow-up, a substantial minority of people also report an improvement of symptoms or the “development” of new symptoms many months or years following mild TBI in both civilian (Dikmen, Machamer, Fann, & Temkin, 2010; Meares et al., 2011; Roe, Sveen, Alvsaker, & Bautz-Holter, 2009) and military populations (Lange et al., 2013; Terrio et al., 2009). The “development” of new postconcussion-like symptoms many months following injury has also been reported in civilian patients who have sustained orthopedic injuries without brain injury (Dikmen et al., 2010; Meares et al., 2011; Terrio et al., 2009).

Though it may not be widely appreciated, researchers have repeatedly demonstrated that many non-TBI factors can cause, maintain, or mimic self-reported postconcussion symptoms (Iverson, Silverberg, Lange, & Zasler, 2013); these postconcussion-like symptoms are clearly not unique to mild TBI alone and often overlap with a number of preexisting and/or co-occurring conditions/circumstances such as psychiatric disorders, personal injury claims, chronic pain, PTSD, soft tissue injuries (Iverson & McCracken, 1997; Lees-Haley & Brown, 1993; Meares et al., 2008; Mickeviciene et al., 2004; Smith-Seemiller, Fow, Kant, & Franzen, 2003), premorbid personality characteristics (e.g., narcissistic, avoidant, dependent, and borderline personality traits; Evered, Ruff, Baldo, & Isomura, 2003; Garden, Sullivan, & Lange, 2010; Hibbard et al., 2000), depression (Iverson, 2006; Lange, Iverson, & Rose, 2011), a diverse range of social-psychological factors (e.g., expectations, misattribution, and an idealized view of preinjury functioning; Davis, 2002; Gunstad & Suhr, 2001; Hilsabeck, Gouvier, & Bolter, 1998; Mittenberg, DiGiulio, Perrin, & Bass, 1992; Suhr & Gunstad, 2005), poor cognitive effort (Iverson, Lange, Brooks, & Ashton Rennison, 2010; Lange, Iverson, Brooks, & Rennison, 2010; Lange, Pancholi, Bhagwat, Anderson-Barnes, & French, 2012; Larrabee, 2003; Wygant et al., 2007), and symptom exaggeration (DeViva & Bloem, 2003; Gervais, Ben-Porath, Wygant, & Green, 2008; Gold & Frueh, 1999; Iverson et al., 2010; Smith & Frueh, 1996). Postconcussion-like symptoms have also been reported in healthy adults, free from neurological, physical, or medical disorders (Gouvier, Uddo-Crane, & Brown, 1988; Iverson & Lange, 2003; Trahan, Ross, & Trahan, 2001). As such, establishing a causative link between postconcussion symptoms and a remote mild TBI can be challenging to say the least.

In a military setting, a patient's clinical presentation following mild TBI may be complicated by concurrent polytrauma and mental health conditions such as PTSD, depression, anxiety, somatoform disorders, and substance abuse; with PTSD and depression the most common (Belanger, Uomoto, & Vanderploeg, 2009; Carlson et al., 2010; Hill, Mobo, & Cullen, 2009; Hoge et al., 2008; Kennedy, Leal, Lewis, Cullen, & Amador, 2010; Schneiderman, Braver, & Kang, 2008). Researchers have found that PTSD and depression largely explain the relation between a history of mild TBI and postconcussion symptom reporting, in addition to other general health problems (Brenner et al., 2010; Hoge et al., 2008; Meares et al., 2011; Polusny et al., 2011; Schneiderman et al., 2008). Exposure to combat situations, and being injured during combat increase vulnerability to the development of PTSD in returning Operation Iraqi Freedom (OIF)/Operation Enduring Freedom (OEF) service members (Hoge, Auchterlonie, & Milliken, 2006; Hoge et al., 2004; Hoge, et al., 2008; Lapierre, Schwegler, & Labauve, 2007; Sareen et al., 2007; Vasterling et al., 2010). Mental health problems also tend to intensify with time (Hoge et al., 2004; Marx et al., 2009; Milliken, Auchterlonie, & Hoge, 2007; Seal et al., 2008) or have a delayed onset (Goodwin et al., 2012; Horesh, Solomon, Keinan, & Ein-Dor, 2013) which may account for some of the variability in postconcussive symptoms reported overtime. In a sample of service members returning from Iraq, less mental health distress was reported immediately upon return from deployment compared with 4–10 months later (Milliken et al., 2007). Polytrauma patients have also been found to endorse high rates of psychological and neurobehavioral symptoms, including memory problems, significant mood symptoms, and amotivation (Frenisy et al., 2006). Recent research has also demonstrated that there tends to be an inverse relation between postconcussion symptom reporting and severity of bodily injury, i.e., as injury severity increases, the frequency of postconcussive symptoms decrease (French et al., 2012; Kennedy, Cullen, Amador, Huey, & Leal, 2010).

To date, many researchers have examined a single, or a small number of factors, that can influence symptom reporting following TBI (e.g., depression, PTSD, “good-old-days” bias). However, few studies have examined a large number of variables concurrently to identify those factors that provide the most unique contribution to postinjury symptom reporting. Of those studies that have examined >4–5 factors, the vast majority of studies have concluded that factors unrelated to brain injury (e.g., depression, PTSD, anxiety, cognitive deficits, fatigue, premorbid anxiety or affective disorders, pain, balance, health status, symptom exaggeration, and poor effort) were the most significant predictors of postconcussion symptom reporting (Hou et al., 2012; McLean et al., 2009; Meares et al., 2008; Sheedy, Harvey, Faux, Geffen, & Shores, 2009; Stulemeijer, van der Werf, Borm, & Vos, 2008). In the only military study to date, Lange and colleagues (2013) examined the influence of 19 factors on postconcussion symptom reporting in 129 U.S. military service members following mild-to-severe TBI. Factors include demographic characteristics, premorbid intellectual ability, TBI severity, injury-related characteristics, psychological variables, symptom exaggeration, and cognitive effort. Postconcussion symptom reporting was not associated with TBI severity, but was most strongly associated with (i) symptom exaggeration, (ii) poor cognitive effort, (iii) depression, and (iv) traumatic stress. In fact, clinically meaningful postconcussion symptom reporting rarely occurred in the absence of these 4 factors (5.6%).

The purpose of this study is to extend the study by Lange and colleagues (2013) by identifying factors that are predictive of postconcussion and posttraumatic stress symptom reporting in a large sample of U.S. military service members who have sustained a TBI. A total of 22 factors were examined that related to (i) demographic variables (gender, military rank, branch of military service, mode of military service), (ii) injury circumstances (mechanism of injury, deployment number when wounded, military operation when wounded, type of military operation when wounded, number of prior blast exposures), (iii) injury severity [loss of consciousness (LOC), posttraumatic amnesia (PTA), TBI severity classification, intracranial abnormality, amputations, and bodily injury severity], (iv) treatment/evaluation (CT ordered after injury, planned disposition for return to duty, and number of days evaluated postinjury), and (v) psychological/physical symptoms (immediate auditory deficits, current auditory deficits, traumatic stress symptoms, and depression). By design, this was an exploratory study with no a priori hypotheses.

Method

Participants

Participants were 1,600 U.S. military service members who sustained a mild-to-moderate TBI and who had been evaluated by the Defense and Veterans Brain Injury Center at one of six U.S. military medical centers following injuries sustained (i) while deployed to Operation Iraqi Freedom (OIF), OEF, or other combat operations related to the Global War on Terrorism (GWOT) or (ii) while on-duty or on-leave within the U.S. or internationally in a non-combat-related incident. The military medical centers and the number of participants from each center were as follows; San Antonio Military Medical Center, Texas (SAMMC; n = 713), Walter Reed National Military Medical Center, Bethesda, MD (formerly Walter Reed Army Medical Center, Washington, DC) (WRNMMC; n = 344), Naval Medical Center San Diego, California (NMCSD; n = 235), 33 Area Branch Clinic Camp Pendleton, California (33ABCCP; n = 218), Naval Hospital 29 Palms, California (NHTP; n = 75), and Wilford Hall Air Force Medical Center, San Antonio, Texas (WHAFMC; n = 15). The majority of the sample were in the Army (59.9%), followed by the Marine (26.9%), Navy (12.2%), Air Force and Coast Guard (1.1%). Rank was as follows: enlisted 1–4 (57.1%), enlisted 5–9 (37.4%), and Chief Warrant (2.1%), Officer (3.4%).

For those participants evaluated at SAMMC and WRNMMC, patients were often medically evacuated for limb loss or systemic injuries, rather than TBI per se. Bodily injury severity ranged from minor (n = 480, 30.0%), moderate (n = 686, 42.9%), serious (n = 290, 18.1%), and severe (n = 113, 7.1%) to critical (n = 31, 1.9%; see Measures and Procedure section for further details). Amputations were present in 4.7% of the sample. Severity of TBI included moderate TBI (n = 98, 6.1%), complicated mild traumatic brain injury (MTBI) (n = 77, 4.8%), uncomplicated MTBI (n = 977, 61.1%), and equivocal MTBI (n = 448, 28.0%; see Clinical Evaluation and TBI Classification section for further details). Intracranial abnormality in the acute phase of injury was present in 7.2% of the sample.

The mean age of the sample was 27.1 years (SD = 7.1) and the majority were male (n = 1,526, 95.4%). All patients were evaluated within 24 months of sustaining their injury (mean = 5.0 months, SD = 5.8, range = 1 day to 23.9 months). The breakdown of time postinjury prior to evaluation was as follows: <1 month (31.4%), 1–<3 months (24.0%), 3–<6 months (16.3%), 6–<12 months (14.6%), and 12–24 months (13.7%). The majority of the sample was injured while deployed during OIF (60.1%), followed by OEF (22.8%), non-combat-related incidents (15.6%), and during other operations related to the GWOT (1.6%). Almost half of the sample had been deployed on one occasion (43.3%); a smaller proportion of the sample had been deployed on two (25.2%), three (8.8%), or four or more (3.2%) occasions (19.5% missing or not applicable). The majority of the sample was injured as a result of an incident involving blast exposure (67.3%, e.g., stepped on IED; motor vehicle hit by IED; building hit by RPG), with 32.7% injured as a result of a non-blast exposure (e.g., head on collision in motor vehicle, pedestrian hit by motor vehicle, assault). The breakdown regarding duration of LOC and PTA was as follows: LOC = none (35.1%), <1 min (31.0%), 1–30 min (22.0%), >30 min to 24 h (0.7%), missing (11.2%); PTA = none (22.1%), <1 min (22.3%), 1–15 min (21.3%), 16–59 min (10.1%), 1–24 h (10.7%), 1–7 days (6.1%), missing (7.3%). Information relating to education level and ethnic background was not available, although a minimum of a High School Diploma or GED is required for military enrollment.

Participant Selection

Patients were selected from a larger sample of 2,316 U.S. military service members who were evaluated at one of the six military medical facilities (SAMMC, n = 885; WRNMMC, n = 619; SDNMC, n = 274; MCBCP, n = 243; MCB29P, n = 98; WHAFMC; n = 183) within the first 24 months of sustaining a suspected or confirmed mild, moderate, severe, or penetrating TBI (between June 2004 and July 2011) and who had completed the Neurobehavioral Symptom Inventory (NSI; Cicerone & Kalmar, 1995) and PTSD Checklist (Blanchard, Jones-Alexander, Buckley, & Forneris, 1996). All patients had agreed to the use of their clinical data for research purposes.

Patients were selected for inclusion in the final sample based on two steps. First, patients were excluded (n = 590, 25.5%; n = 1,726 remaining) if they did not meet the following criteria: (i) sustained a closed TBI (n = 2,278, 98.4% of larger sample), (ii) had sufficient information available that could be used to confidently classify them as having sustained a mild or moderate TBI (n = 2,032, 87.7% of larger sample [i.e., 80.7% mild TBI, 7.0% moderate TBI]), and (iii) had an Abbreviated Injury Scale (Baker, O'Neill, Haddon, & Long, 1974) completed (n = 1,916, 82.7% of larger sample). Second, patients were further excluded (n = 126, 7.3%; n = 1,600 remaining) if they had missing information on the majority of demographic and injury-related variables of interest (e.g., age, gender, rank, branch of service, mode of service, operation where wounded, mechanism of injury, amputations, immediate auditory deficit, and return to duty disposition).

Clinical Evaluation and TBI Classification

Diagnosis and classification of TBI severity was based on a routine comprehensive clinical screening evaluation undertaken by medical/healthcare professionals at each respective military medical facility. For the large majority of patients, these evaluations are completed by a Physician's Assistant or Nurse who was trained to evaluate the presence and severity of TBI. In some cases, evaluations were also completed by other healthcare professionals such as Neuropsychologists and Social Workers who have specialty training to evaluate TBI. TBI evaluations typically include (i) a patient interview, (ii) a comprehensive medical chart review (including the review of in-theater medical records when available), (iii) case conferencing, and (iv) family interview and collection of other collateral information (if available). Self-reported symptoms are routinely obtained during the TBI evaluation but are not used for diagnostic or classification purposes (i.e., NSI [Cicerone & Kalmar, 1995] and PTSD Checklist-Civilian [PCL-C; Weathers, Litz, Huska, & Keane, 1994]).

For the purposes of this study, classification of TBI severity was based on the presence and duration of LOC, presence and duration of PTA, and presence/absence of trauma-related intracranial abnormality on neuroradiological scans. For some participants, the presence/absence of an alteration of consciousness (AOC) was also used. Although use of Glasgow Coma Scale (GCS) scores for classification purposes is consistent with commonly used diagnostic criteria for TBI (Management of Concussion/nTBI Working Group, 2009; Mild Traumatic Brain Injury Committee, American Congress of Rehabilitation Medicine, & Head Injury Interdisciplinary Special Interest Group, 1993; World Health Organization, 1992), GCS scores were not available in this sample. TBI severity categories were defined as follows: (i) moderate TBI: LOC > 30 min to 24 h, PTA 1–7 days, and the presence or absence of intracranial abnormality (or no neuroimaging information available); (ii) complicated mild TBI: LOC ≤ 30 min, PTA < 24 h, and the presence of intracranial abnormality; (iii) uncomplicated mild TBI: LOC ≤ 30 min, PTA < 24 h, and the absence of intracranial abnormality; (iv) equivocal mild TBI: PTA absent, LOC absent, AOC present.

For those patients with LOC and PTA in the mild range, a classification of mild TBI was assigned regardless of the absence or presence of intracranial abnormality. It is acknowledged that this practice is incongruent with the Department of Defense clinical guidelines (Managment of Concussion/nTBI Working Group, 2009) that recommend classifying any patient with intracranial abnormality as having a “greater than mild injury” (p. 16). However, for the purposes of research, our preference is to classify those patients with evidence of intracranial abnormality and LOC and PTA in the mild range, as having a “complicated mild TBI” (rather than a moderate TBI). The importance of the distinction between complicated and uncomplicated mild TBI has been discussed elsewhere (Iverson, Lange, Gaetz, & Zasler, 2007). In addition, patients who experienced a brief period of AOC, but did not experience the presence of LOC or PTA, were not included in the uncomplicated mild TBI group. It is again acknowledged that this practice is incongruent with the Department of Defense clinical guidelines (Management of Concussion/nTBI Working Group, 2009) that recommend classifying any patient with AOC, in the absence of LOC and PTA, as having a mild TBI (and by definition an uncomplicated mild TBI). However, for the purposes of research, our preference was to create separate and distinct mild TBI groups that were clearly defined by the presence or absence of LOC and/or PTA.

Measures and Procedure

The NSI (Cicerone & Kalmar, 1995) is a 22-item measure designed to evaluate self-reported postconcussion symptoms (e.g., headache, balance, nausea, etc.). The NSI requires the test taker to rate the presence/severity of each symptom on a 5-point scale (none, mild, moderate, severe, and very severe). A total score is obtained by summing the ratings for the 22 items (range = 0–88). Based on DSM-IV-TR Category C and D research criteria for postconcussional disorder (PCD), participant's responses on the NSI were further classified as “clinically elevated” (PCD-High) or “within normal limits” (PCD-Low). Clinically elevated postconcussion symptoms were defined as the endorsement of three or more Category C symptoms as moderate or higher and the endorsement of subjective complaints of attention or memory problems as moderate or higher (i.e., Category B; note that Category B criteria require objective evidence of cognitive impairment in attention or memory. For the purposes of this study, subjective reports of these cognitive complaints were used as a proxy). It is important to appreciate that symptom endorsement on the NSI cannot be used in isolation to evaluate whether a person meets DSM-IV-TR research criteria for PCD. Diagnosis of PCD is complicated, challenging, and requires a comprehensive clinical evaluation not included in this study (see Iverson & colleagues, 2013 for a comprehensive discussion). A number of DSM-IV-TR criteria were not evaluated (e.g., Category B = objective evidence of difficulty in attention/memory; Category C = symptoms last at least 3 months; Category D = substantial worsening of preexisting symptoms; Category E = impairment in social or occupational functioning). Rather, endorsement of NSI items that meet DSM-IV-TR symptom criteria for PCD simply reflects clinically elevated postconcussion symptom reporting. In addition to the above scores, a single item from the NSI (i.e., Item 20) was also used as a separate measure of depression in lieu of other more comprehensive symptoms ratings or diagnostic interviews.

The PCL-C Version (Blanchard et al., 1996) is a 17-item measure designed to evaluate self-reported PTSD symptoms. The PCL-C was patterned specifically after the DSM-IV-TR (American Psychiatric Association, 1994) criteria to address Category B, C, and D symptom criteria for PTSD. The PCL-C requires the test taker to rate the presence/severity of each symptom on a 5-point scale (not at all, a little bit, moderately, quite a bit, extremely). A total score is obtained by summing the ratings for the 17 items (range = 17–85). Based on DSM-IV-TR symptom criteria for PTSD, participant's responses on the PCL-C were further classified as “clinically elevated” (PTSD-High) or “within normal limits” (PTSD-Low). A person was classified as having clinically elevated self-reported symptoms of PTSD if the respondent endorsed (i) one or more of the Criterion B symptoms as moderate or higher, (ii) three or more of the Criterion C symptoms as moderate or higher, and (iii) two or more of the Criterion D symptoms as moderate or higher. It is also important to appreciate that symptom endorsement on the PCL-C that is consistent with DSM-IV-TR Category B, C, and D symptom criteria does not equate to a diagnosis of PTSD. Diagnosis of PTSD requires a comprehensive clinical evaluation not included in this study A number of other DSM-IV-TR criteria were not evaluated (Category E = symptoms last more than 1 month; Category F = symptoms cause significant distress or impairment in social, occupational, or other important areas of functioning). Rather, endorsement of symptoms on the PCL-C that meet DSM-IV-TR symptom criteria simply reflects clinically elevated endorsement of PTSD symptoms.

The Abbreviated Injury Scale (Baker et al., 1974) is an anatomically based, consensus-derived, global severity scoring system that classifies injuries to the body categorized into six main regions; (i) Region 1 = Head/Neck/Cervical Spine; (ii) Region 2 = Face; (iii) Region 3 = Thorax/Thoracic Spine; (iv) Region 4 = Abdomen/Lumbar Spine; (v) Region 5 = Extremities; (vi) Region 6 = External/Burns. Injuries in each region are rated on a 6-point ordinal scale that classifies injury severity as minor (i), moderate (ii), serious (iii), severe (iv), critical (v), or maximal (6). The AIS is traditionally interpreted using the Injury Severity Score (ISS). The ISS is calculated by summing the squares of the highest AIS severity codes in each of the three most severely injured body regions. The ISS ranges from 1 to 75. For the purposes of this study, a modified ISS score was calculated (ISSmod) designed to include only extracranial injuries. All AIS codes referring to intracranial injuries were not included in the calculation of ISSmod. The ISSmod, however, was calculated in the same manner as the ISS score described previously. Participants were classified into five bodily injury severity categories based on recommended ISS scores by Stevenson, Segui-Gomez, Lescohier, Di Scala, and McDonald-Smith (2001): minor (ISS 1–3), moderate (ISS 4–8), serious (ISS 9–15), severe (ISS 16–24), and critical (ISS 25–75).

The protocols under which these data were collected were approved by the Institutional Review Board of SAMMC, WRNMMC, NMCSD, 33ABCCP, and NHTP. This study was completed in accordance with the guidelines of the Declaration of Helsinki. For SDNMC, it is further noted that the voluntary informed consent of the subjects used in this research was obtained as required by SECNAVINST 3900.39D and the investigator(s) adhered to the policies regarding the protection of human subjects as prescribed by Code of Federal Regulations Title 45, Volume 1, Part 46; Title 32, Chapter 1, Part 219; and Title 21, Chapter 1, Part 50 (Protection of Human Subjects).

Group Classification and Analysis Goals

Using responses from the NSI and PCL-C, the sample was divided into four mutually exclusive groups based on DSM-IV-TR symptom criteria for PCD and PTSD as described previously (note once again that endorsement of NSI and PCL-C items that meet DSM-IV-TR symptom criteria for PCD or PTSD simply reflect clinically elevated symptom reporting only, and not a diagnosis per se). The mutually exclusive groups included three symptomatic groups (PCD-High [n = 361, 22.6%, i.e., PCD-High and PTSD-Low], PTSD-High [n = 60, 3.8%, i.e., PTSD-High and PCD-Low], and PCD/PTSD-High [n = 488, n = 30.5%]) and one asymptomatic control group [PCD/PTSD-Low (n = 691, 43.2%)]. In order to examine risk factors for high postconcussion and posttraumatic stress symptom reporting, our goal was to complete a series of two-group comparisons by comparing the asymptomatic control group (i.e., PCD/PTSD-Low) with each of the three symptomatic groups separately (i.e., PCD-High, PTSD-High, and PCD/PTSD-High). However, due to the small sample size of the PTSD-High group (n = 60), this group was not included in the following analyses. The following analyses consisted of two stages. First, to examine risk factors for high postconcussion symptom reporting, the asymptomatic control group (i.e., PCD/PTSD-Low) was compared with the PCD-High group. Second, to examine risk factors for high postconcussion and PTSD symptom reporting, the asymptomatic control group (i.e., PCD/PTSD-Low) was compared with the PCD/PTSD-High group.

Results

Risk Factors for High Postconcussion Symptom Reporting

Exploratory group comparisons

Descriptive statistics and group comparisons of demographic and injury-related characteristics, for the PCD-High group and PCD/PTSD-Low group, is presented in Table 1. There were no significant differences between groups for age, number of injury mechanisms, deployment number when injured, military rank, mechanism of injury, LOC, PTA, injury-related intracranial abnormality, CT scan ordered postinjury, or planned disposition for return to duty. There were significant differences for days postinjury, ISSmod scores and severity classifications, PCL-C total score, NSI item 20-Depression and severity classifications, gender, branch of service, mode of service, operation where wounded, type of operation where wounded, TBI severity, amputations, and auditory deficit present at the time of injury and at the time of evaluation (range: p < .001–.034).

Table 1.

Comparison of demographic and injury severity characteristics between PCD-High and PCD/PTSD-Low groups

 PCD-High
 
PCD/PTSD-Low
 
p d    
 M SD M SD      
Age (in years) 27.0 7.1 26.8 7.0 .735 0.02 – – – 
Days tested postinjury 153.6 179.0 107.7 152.3 <.001 0.28 – – – 
Bodily injury severity (AIS-ISSmod)a 5.9 5.2 8.0 7.9 <.001 0.30 – – – 
Number of injury mechanisms 1.2 0.4 1.1 0.4 .239 0.08 – – – 
Deployment numberb 1.7 1.1 1.7 1.0 .783 0.01 – – – 
PCL-C total score 37.3 8.4 25.9 7.7 <.001 1.44 – – – 
NSI item 20 (Depression) 0.8 0.9 0.3 0.6 <.001 0.74 – – – 
 p OR 95% CI RR 95% CI 
Gender 
 Female 22 48.9 23 51.1 .035 1.89 1.00–3.57 1.45 1.00–1.93 
 Male 339 33.7 668 66.3      
Rank 
 Enlisted 343 34.8 642 65.2 .184 1.45 0.81–2.64 1.30 0.87–2.06 
 Officer + Chief Warrant 18 26.9 49 73.1      
Branch of servicec 
 Army/marines 322 35.8 577 64.2 .013 1.63 1.09–2.45 1.41 1.06–1.92 
 Navy/AirF/CoastG 39 25.5 114 74.5      
Mode of service 
 Reservist/Guard 162 38.8 256 61.2 .014 1.38 1.06–1.81 1.24 1.04–1.46 
 Regular 199 31.4 435 68.5      
Deployment numberc 
 First/second 260 36.8 447 63.2 .111d 1.39 0.91–2.14 1.25 0.94–1.71 
 Third or more 38 29.5 91 70.5      
 Missing/NA 63 29.2 153 70.8      
Where woundedc 
 Other GWOT 12 66.7 33.3 .004 3.93 1.36–11.83 1.98 1.21–2.56 
 OIF/OEF/non-combat 349 33.8 685 66.2      
Where wounded 
 Combat zone 319 36.4 557 63.6 .001 1.83 1.24–2.70 1.53 1.16–2.06 
 Non-combat zone 42 23.9 134 76.1      
Mechanism of Injury 
 Blast 250 35.8 449 64.2 .163 1.21 0.92–1.61 1.14 0.94–1.38 
 Non-blast 111 31.4 242 68.6      
Loss of consciousnessc 
 Present 198 35.9 354 64.1 .605d 1.08 0.81–1.43 1.05 0.87–1.26 
 Absent 129 34.2 248 65.8      
 Unknown/missing 34 27.6 89 72.4      
Posttraumatic amnesiac 
 Present 266 35.5 483 64.5 .738d 1.05 0.77–1.45 1.04 0.85–1.28 
 Absent 81 34.3 155 65.7      
 Unknown/missing 14 20.9 53 79.1      
TBI severityc 
 EqMTBI/UncMTBI 348 35.1 644 64.9 .034 1.95 1.01–3.85 1.62 1.01–2.84 
 Comp MTBI/Mod TBI 13 21.7 47 78.3      
Intracranial Abn 
 Absent & No CT/MRI 337 35.1 624 64.9 .095 1.51 0.91–2.52 1.33 0.94–1.98 
 Present 24 26.4 67 73.6      
CT completed 
 No 125 35.6 226 64.4 .646d 1.07 0.81–1.41 1.04 0.87–1.25 
 Yes 230 34.2 443 65.8      
 NA/unknown/missing 21.4 22 78.6      
Amputations 
 Absent 349 35.3 641 64.7 .011 2.27 1.15–4.56 1.82 1.10–3.29 
 Present 12 19.4 50 80.6      
Bod Inj Sev (ISSmod)c 
 Minor/moderate 273 38.3 440 61.7 <.001 2.15 1.32–3.50 1.71 1.20–2.52 
 Severe or higher 26 22.4 90 77.6      
Immediate auditory deficit 
 Present 182 41.6 256 58.4 <.001 1.73 1.32–2.26 1.43 1.20–1.69 
 Absent 179 29.2 435 70.8      
Current auditory deficit 
 Present 145 43.8 186 56.2 <.001d 1.68 1.24–2.26 1.38 1.15–1.66 
 Absent 154 31.8 331 68.2      
 Not applicable 62 26.3 174 73.7      
Planned disposition 
 Further treatment/care 249 34.6 470 65.4 .751 1.05 0.79–1.39 1.03 0.86–1.25 
 Return to duty 112 33.6 221 66.4      
ASD/PTSD (≥mild Sx) 
 Present 192 56.8 146 43.2 <.001 4.24 3.19–5.64 2.40 2.04–2.81 
 Absent 169 23.7 545 76.3      
Days postinjuryc 
 3 or more months 162 43.4 211 56.6 <.001 1.85 1.41–2.43 1.48 1.25–1.75 
 <3 months 199 29.3 480 70.7      
Depression (NSI-20) 
 Moderate or higher 84 70.6 35 29.4 <.001 5.68 3.67–8.83 2.38 2.01–2.72 
 None or mild 277 29.7 656 70.3      
Depression (NSI-20) 
 Severe or higher 19 76.0 24.0 <.001 6.34 2.37–17.91 2.28 1.62–2.72 
 None, mild, or moderate 342 33.3 685 66.7      
 PCD-High
 
PCD/PTSD-Low
 
p d    
 M SD M SD      
Age (in years) 27.0 7.1 26.8 7.0 .735 0.02 – – – 
Days tested postinjury 153.6 179.0 107.7 152.3 <.001 0.28 – – – 
Bodily injury severity (AIS-ISSmod)a 5.9 5.2 8.0 7.9 <.001 0.30 – – – 
Number of injury mechanisms 1.2 0.4 1.1 0.4 .239 0.08 – – – 
Deployment numberb 1.7 1.1 1.7 1.0 .783 0.01 – – – 
PCL-C total score 37.3 8.4 25.9 7.7 <.001 1.44 – – – 
NSI item 20 (Depression) 0.8 0.9 0.3 0.6 <.001 0.74 – – – 
 p OR 95% CI RR 95% CI 
Gender 
 Female 22 48.9 23 51.1 .035 1.89 1.00–3.57 1.45 1.00–1.93 
 Male 339 33.7 668 66.3      
Rank 
 Enlisted 343 34.8 642 65.2 .184 1.45 0.81–2.64 1.30 0.87–2.06 
 Officer + Chief Warrant 18 26.9 49 73.1      
Branch of servicec 
 Army/marines 322 35.8 577 64.2 .013 1.63 1.09–2.45 1.41 1.06–1.92 
 Navy/AirF/CoastG 39 25.5 114 74.5      
Mode of service 
 Reservist/Guard 162 38.8 256 61.2 .014 1.38 1.06–1.81 1.24 1.04–1.46 
 Regular 199 31.4 435 68.5      
Deployment numberc 
 First/second 260 36.8 447 63.2 .111d 1.39 0.91–2.14 1.25 0.94–1.71 
 Third or more 38 29.5 91 70.5      
 Missing/NA 63 29.2 153 70.8      
Where woundedc 
 Other GWOT 12 66.7 33.3 .004 3.93 1.36–11.83 1.98 1.21–2.56 
 OIF/OEF/non-combat 349 33.8 685 66.2      
Where wounded 
 Combat zone 319 36.4 557 63.6 .001 1.83 1.24–2.70 1.53 1.16–2.06 
 Non-combat zone 42 23.9 134 76.1      
Mechanism of Injury 
 Blast 250 35.8 449 64.2 .163 1.21 0.92–1.61 1.14 0.94–1.38 
 Non-blast 111 31.4 242 68.6      
Loss of consciousnessc 
 Present 198 35.9 354 64.1 .605d 1.08 0.81–1.43 1.05 0.87–1.26 
 Absent 129 34.2 248 65.8      
 Unknown/missing 34 27.6 89 72.4      
Posttraumatic amnesiac 
 Present 266 35.5 483 64.5 .738d 1.05 0.77–1.45 1.04 0.85–1.28 
 Absent 81 34.3 155 65.7      
 Unknown/missing 14 20.9 53 79.1      
TBI severityc 
 EqMTBI/UncMTBI 348 35.1 644 64.9 .034 1.95 1.01–3.85 1.62 1.01–2.84 
 Comp MTBI/Mod TBI 13 21.7 47 78.3      
Intracranial Abn 
 Absent & No CT/MRI 337 35.1 624 64.9 .095 1.51 0.91–2.52 1.33 0.94–1.98 
 Present 24 26.4 67 73.6      
CT completed 
 No 125 35.6 226 64.4 .646d 1.07 0.81–1.41 1.04 0.87–1.25 
 Yes 230 34.2 443 65.8      
 NA/unknown/missing 21.4 22 78.6      
Amputations 
 Absent 349 35.3 641 64.7 .011 2.27 1.15–4.56 1.82 1.10–3.29 
 Present 12 19.4 50 80.6      
Bod Inj Sev (ISSmod)c 
 Minor/moderate 273 38.3 440 61.7 <.001 2.15 1.32–3.50 1.71 1.20–2.52 
 Severe or higher 26 22.4 90 77.6      
Immediate auditory deficit 
 Present 182 41.6 256 58.4 <.001 1.73 1.32–2.26 1.43 1.20–1.69 
 Absent 179 29.2 435 70.8      
Current auditory deficit 
 Present 145 43.8 186 56.2 <.001d 1.68 1.24–2.26 1.38 1.15–1.66 
 Absent 154 31.8 331 68.2      
 Not applicable 62 26.3 174 73.7      
Planned disposition 
 Further treatment/care 249 34.6 470 65.4 .751 1.05 0.79–1.39 1.03 0.86–1.25 
 Return to duty 112 33.6 221 66.4      
ASD/PTSD (≥mild Sx) 
 Present 192 56.8 146 43.2 <.001 4.24 3.19–5.64 2.40 2.04–2.81 
 Absent 169 23.7 545 76.3      
Days postinjuryc 
 3 or more months 162 43.4 211 56.6 <.001 1.85 1.41–2.43 1.48 1.25–1.75 
 <3 months 199 29.3 480 70.7      
Depression (NSI-20) 
 Moderate or higher 84 70.6 35 29.4 <.001 5.68 3.67–8.83 2.38 2.01–2.72 
 None or mild 277 29.7 656 70.3      
Depression (NSI-20) 
 Severe or higher 19 76.0 24.0 <.001 6.34 2.37–17.91 2.28 1.62–2.72 
 None, mild, or moderate 342 33.3 685 66.7      

Notes:n = 1,052 (PCD-High, n = 361; PCD/PTSD-Low, n = 691). ISSmod = modified Injury Severity Scale; PCL-C = PTSD Checklist-Civilian Version; NSI = Neurobehavioral Symptom Inventory; OIF = Operation Iraqi Freedom; OEF = Operation Enduring Freedom; GWOT = Global War on Terror; MTBI = mild traumatic brain injury; AOC = alteration of consciousness; TBI = traumatic brain injury; CT = computed tomography; MRI = magnetic resonance imaging.

an = 918 (PCD-High, n = 327; PCD/PTSD-Low, n = 591).

bn = 836 (PCD-High, n = 298; PCD/PTSD-Low, n = 538).

cThese data were derived from a larger number of categories that were collapsed together based on common percentages. These additional data are available on request.

dp-value generated by ignoring missing values.

Examination of odds ratios (OR) and relative risk (RR) values revealed that the PCD-High group was statistically more likely to be (i) female, (ii) serving in the Army or Marine Corps (versus the Air Force, Navy, or Coast Guard), (iii) serving as a Reservist or National Guard (versus Regular Active Duty), (iv) been injured while deployed in a combat zone, and in particular, while deployed during an operation relating to the GWOT (versus OEF/OIF/non-combat). In addition, the PCD-High group was statistically more likely to be (v) evaluated three or more months postinjury, (vi) had an auditory deficit at the time of evaluation and at the time of injury, (vii) had no amputations, (viii) sustained a minor/moderate bodily injury (versus a more severe bodily injury), (ix) sustained a TBI that was classified as uncomplicated MTBI, equivocal MTBI, or moderate TBI (versus complicated MTBI), (x) endorsed mild symptoms of PTSD on the PCL-C, and (xi) report the presence of depression as moderate or higher, and severe or higher (range: OR = 1.38–6.34; RR = 1.24–2.40).

Logistic regression analyses

To examine which factors provide the most unique contribution towards the prediction of postconcussion symptom reporting, logistic regression analyses were undertaken to determine if select factors from Table 1 could identify participants in the PCD-High versus PCD/PTSD-Low group. Factors were selected if they reflected statistically and clinically meaningful differences between groups. Due to the large sample size and subsequent high statistical power, many variables were found to be statistically significant between groups (i.e., p < .05) but were not considered clinically meaningful (i.e., small Cohen's effect sizes or OR). As such, variables were selected only if there were statistically significant group differences and an OR ≥ 2 or Cohen's d ≥ .30. Variables that met this initial criterion were as follows: (i) ISSmod score, (ii) PCL-C total score, (iii) NSI item 20-Depression, (iv) military operation where wounded, (v) amputations, (vi) ISSmod severity classification, (vii) DSM-IV-TR mild PTSD classification, (viii) moderate or higher depression classification, and (ix) severe or higher depression classification. Due to the overlap of some variables, a final list of four factors was selected for analysis by favoring the inclusion of continuous variables, and excluding variables that were redundant or overlapping: (i) NSI item 20-Depression (excluded depression severity classifications of moderate or higher and severe or higher), (ii) ISSmod score (excluded amputations and ISSmod severity classifications), (iii) PCL-C total score, and (iv) military operation where wounded.

For the logistic regression analysis, all four factors were entered simultaneously as the dependent variables and group membership as the independent variable. All four variables were significant predictors of group membership (i.e., NSI Item 20-Depression [p < .001], PCL-C total [p < .001], military operation where wounded [p = .012], ISSmod score [p = .002]) accounting for 43.2% of the variance (Nagelkerke R2; p < .001). Overall, 78.1% of participants were correctly classified using this criterion (59.3% PCD-High; 88.0% PCD/PTSD-Low).

Five additional exploratory analyses were undertaken using one or more of the four factors in each model: (i) depression, (ii) PCL-C total, (iii) ISSmod (iv) military operation where wounded, and (v) depression and PCL-C total. For all five logistic regression analyses, the selected factor(s) were entered as the dependent variable(s), and group membership as the independent variable. All five models were significant predictors of group membership (all p < .001). The highest classification rates were found when using PCL-C total (58.2% PCD-High; 88.1% PCD/PTSD-Low; R2 = 40.8%) and depression and PCL-C total (57.1% PCD-High; 87.6% PCD/PTSD-Low; R2 = 41.5%), followed by depression (23.3% PCD-High; 94.9% PCD/PTSD-Low; R2 = 13.6%), military operation where wounded (3.3% PCD-High; 99.1% PCD/PTSD-Low; R2 = 1.0%), and ISSmod (0% PCD-High; 100% PCD/PTSD-Low; R2 = 2.9%).

OR and RR values for classification rates from all Logistic Regression analyses previously are presented in Table 2 (top half of table). The highest OR and RR values were found when combining all four factors (OR = 10.66, RR = 4.94). However, equally high OR and RR values were found when using PCL-C total (OR = 10.33, RR = 4.90) or PCL-C and depression combined (OR = 9.35, RR = 4.59). OR and RR values were moderately high when using depression (OR = 5.68, RR = 4.59), and moderate when using military operation where wounded (OR = 3.93; RR = 3.83). OR and RR values for ISSmod were not able to be calculated due to the poor classification rates.

Table 2.

Comparison of classification accuracy of selected factors to identify the PCD-High versus PCD/PTSD-Low group

  PCD-High
 
PCD/PTSD Low
 
p OR 95% CI RR 95% CI 
n n 
Logistic regression analyses 
 Model: 4 factorsa 
  Present 214 59.3 147 40.7 <.001 10.66 7.72–14.74 4.94 3.99–6.13 
  Absent 83 12.0 608 88.0      
 Model 1: depression 
  Present 84 23.3 277 76.7 <.001 5.68 3.67–8.83 4.59 3.12–6.82 
  Absent 35 5.1 656 94.9      
 Model 2: PCL-C total 
  Present 210 58.2 151 41.8 <.001 10.33 7.48–14.28 4.90 3.95–6.10 
  Absent 82 11.9 609 88.1      
 Model 3: ISSmod 
  Present 361 100 <.001 – – – – 
  Absent 691 100      
 Model 4: location of injury 
  Present 12 3.3 349 96.7 <.001 3.93 1.36–11.83 3.83 1.35–11.37 
  Absent 0.9 685 99.1      
 Model 5: depression and PCL-C 
  Present 206 57.1 155 42.9 <.001 9.35 6.80–12.87 4.59 3.71–5.69 
  Absent 86 12.4 605 87.6      
Clinical algorithms 
 DEP and mild PTSD 
  Present 59 77.6 17 22.4 <.001 7.75 4.31–14.06 2.51 2.10–2.84 
  Absent 302 30.9 674 69.1      
 DEP or mild PTSD 
  Present 217 57.0 164 43.0 <.001 4.84 3.65–6.43 2.65 2.24–3.14 
  Absent 144 21.5 527 78.5      
 (DEP or mild PTSD) and ISSmod 
  Present 161 58.8 113 41.2 <.001 4.12 3.05–5.56 2.29 1.95–2.66 
  Absent 200 25.7 578 74.3      
 DEP or mild PTSD or ISSmod 
  Present 329 40.1 491 59.9 <.001 4.19 2.77–6.37 2.91 2.08–4.16 
  Absent 32 13.8 200 86.2      
 (DEP or mild PTSD) and wound GWOT 
  Present 87.5 12.5 <.001 13.64 1.70–296.32 2.58 1.37–2.40 
  Absent 354 33.9 690 66.1      
 DEP or mild PTSD or wound GWOT 
  Present 222 56.8 169 43.2 <.001 4.93 3.72–6.55 2.70 2.28–3.20 
  Absent 139 21.0 522 79.0      
  PCD-High
 
PCD/PTSD Low
 
p OR 95% CI RR 95% CI 
n n 
Logistic regression analyses 
 Model: 4 factorsa 
  Present 214 59.3 147 40.7 <.001 10.66 7.72–14.74 4.94 3.99–6.13 
  Absent 83 12.0 608 88.0      
 Model 1: depression 
  Present 84 23.3 277 76.7 <.001 5.68 3.67–8.83 4.59 3.12–6.82 
  Absent 35 5.1 656 94.9      
 Model 2: PCL-C total 
  Present 210 58.2 151 41.8 <.001 10.33 7.48–14.28 4.90 3.95–6.10 
  Absent 82 11.9 609 88.1      
 Model 3: ISSmod 
  Present 361 100 <.001 – – – – 
  Absent 691 100      
 Model 4: location of injury 
  Present 12 3.3 349 96.7 <.001 3.93 1.36–11.83 3.83 1.35–11.37 
  Absent 0.9 685 99.1      
 Model 5: depression and PCL-C 
  Present 206 57.1 155 42.9 <.001 9.35 6.80–12.87 4.59 3.71–5.69 
  Absent 86 12.4 605 87.6      
Clinical algorithms 
 DEP and mild PTSD 
  Present 59 77.6 17 22.4 <.001 7.75 4.31–14.06 2.51 2.10–2.84 
  Absent 302 30.9 674 69.1      
 DEP or mild PTSD 
  Present 217 57.0 164 43.0 <.001 4.84 3.65–6.43 2.65 2.24–3.14 
  Absent 144 21.5 527 78.5      
 (DEP or mild PTSD) and ISSmod 
  Present 161 58.8 113 41.2 <.001 4.12 3.05–5.56 2.29 1.95–2.66 
  Absent 200 25.7 578 74.3      
 DEP or mild PTSD or ISSmod 
  Present 329 40.1 491 59.9 <.001 4.19 2.77–6.37 2.91 2.08–4.16 
  Absent 32 13.8 200 86.2      
 (DEP or mild PTSD) and wound GWOT 
  Present 87.5 12.5 <.001 13.64 1.70–296.32 2.58 1.37–2.40 
  Absent 354 33.9 690 66.1      
 DEP or mild PTSD or wound GWOT 
  Present 222 56.8 169 43.2 <.001 4.93 3.72–6.55 2.70 2.28–3.20 
  Absent 139 21.0 522 79.0      

Notes:n = 1,052 (PCD-High, n = 361; PCD/PTSD-Low, n = 691). ISSmod = modified Injury Severity Scale; PCL-C = PTSD Checklist-Civilian Version.

aDepression, PCL-C total score, ISSmod, and operation where wounded.

Clinical algorithms

Clinical algorithms using measures of depression, bodily injury severity, PTSD symptoms, and military operation where wounded categories were used to further determine if these “risk factors” could differentiate participants in the PCD-High and PCD/PTSD-Low group. Cutoff scores and factors were evaluated singularly, and in combination, using the following criterion as “risk factors” for PCD: (i) depression reported as moderate or higher in severity on item 20 of the NSI, (ii) bodily injury severity classified as minor/moderate by the ISSmod score, (iii) endorsement of PCL-C items that met DSM-IV-TR symptom criteria for PTSD based on mild or higher symptom severity, and (iv) having sustained an injury during a military operation related to the GWOT. Variables and cutoffs were selected based on their ability to discriminate between the PCD-High and PCD/PTSD-Low groups in Table 1. OR and RR values for these variables are presented in Table 2 (bottom half of table).

When using depression and PTSD criteria only, the highest OR and RR values were found when using an algorithm that combined “depression and mild PTSD” (OR = 7.75; RR = 2.51), followed by “depression or mild PTSD” (OR = 4.84; RR = 2.65). The base rate of PCD, in the absence of depression and mild PTSD, was 39%. When using depression and PTSD criteria combined with one of the other two remaining risk factors, similar moderate OR and RR values were found when using an algorithm that combined (i) “depression or mild PTSD or injured during GWOT, (ii) “depression or mild PTSD or minor/moderate ISSmod score”, and (iii) “depression or mild PTSD and minor/moderate ISSmod score” (range: OR = 4.12–4.93; RR = 2.29–2.91). Although there was a very high OR when using the algorithm that combines “depression or mild PTSD and injured during GWOT” (OR = 13.64; RR = 2.58), this value should be viewed with caution due to the unacceptably wide 95% CI band (1.70 to 296.32) that makes this value meaningless.

Risk Factors for High Postconcussion and PTSD Symptom Reporting

Exploratory group comparisons

Descriptive statistics and group comparisons of demographic and injury-related characteristics, for the PCD/PTSD-High group and PCD/PTSD-Low group, is presented in Table 3. There were no significant differences between groups for age, number of injury mechanisms, deployment number when injured, mechanism of injury, LOC, PTA, or planned disposition for return to duty. There was however significant differences for all remaining factors. For the continuous variables, the PCD/PTSD-High group had a significantly lower score on ISSmod (p < .001, d = 41, medium effect size), a significantly higher score on NSI item 20-Depression (p < .001, d = 2.07, very large effect size), and had been evaluated a significantly higher number of days postinjury (p < .001, d = .60, medium effect size).

Table 3.

Comparison of demographic and injury severity characteristics between PCD/PTSD-High and PCD/PTSD-Low groups

 PCD/PTSD-High
 
PCD/PTSD-Low
 
p d    
 M SD M SD      
Age (in years) 27.5 7.3 26.8 7.0 .104 .10 – – – 
Days postinjury (NSI) 208.8 191.2 107.7 152.3 <.001 .60 – – – 
Bodily injury severity (ISSmod)a 5.2 5.4 8.0 7.9 <.001 .41 – – – 
Number of injury mechanisms 1.2 0.4 1.1 0.4 .339 .05 – – – 
Deployment numberb 1.7 0.9 1.7 1.0 .631 .06 – – – 
PCL-C total score 60.6 10.5 25.9 7.7 <.001 3.93 – – – 
NSI item 20 (Depression) 2.0 1.1 0.3 0.6 <.001 2.07 – – – 
 n n p OR 95% CI RR 95% CI 
Gender 
 Female 28 54.9 23 45.1 .045 1.77 0.97–3.22 1.35 0.98–1.70 
 Male 460 40.8 668 59.2      
Rank 
 Enlisted (E1–E9) 468 42.2 642 57.8 .031 1.79 1.02–3.16 1.46 1.01–2.23 
 Officer (O1–O7) + CW 20 29.0 49 71.0      
Branch of servicec 
 All other 447 43.3 585 56.7 <.001 7.57 5.30–10.84 4.72 3.49–6.48 
 Navy 41 27.9 106 72.1      
Mode of service 
 Reservist/Guard 237 48.1 256 51.9 <.001 1.60 1.26–2.04 1.31 1.14–1.51 
 Regular 251 36.6 435 63.4      
Deployment numberc 
 First/second 348 43.8 447 56.2 .201d 1.27 0.87–1.85 1.15 0.92–1.47 
 Third or more 56 38.1 91 61.9      
 Missing/NA 84 35.4 153 64.6      
Operation woundedc 
 OIF/other GWOT 348 48.7 366 51.3 <.001 2.21 1.71–2.85 1.62 1.38–1.91 
 All other 140 30.1 325 69.9      
Type of operation 
 Combat zone 426 43.3 557 56.7 .001 1.65 1.18–2.32 1.37 1.10–1.73 
 Non-combat zone 62 31.6 134 68.4      
Mechanism of injury 
 Blast 337 42.9 449 57.1 .143 1.20 0.93–1.55 1.12 0.96–1.31 
 Non-blast 151 38.4 242 61.6      
Loss of consciousnessc 
 Present 271 43.4 354 56.6 .276d 1.15 0.89–1.49 1.09 0.93–1.27 
 Absent 165 40.0 248 60.0      
 Unknown/missing 52 36.9 89 63.1      
Posttraumatic amnesiac 
 Present 338 41.2 483 58.8 .874d 1.02 0.76–1.37 1.01 0.86–1.21 
 Absent 106 40.6 155 59.4      
 Unknown/missing 44 45.4 53 54.6      
TBI severityc 
 All other TBI 473 42.3 644 57.7 .005 2.30 1.23–4.36 1.75 1.14–2.92 
 Complicated MTBI 15 24.2 47 75.8      
Intracranial Abn 
 Absent and No CT/MRI 465 42.7 624 57.3 .002 2.17 1.30–3.65 1.67 1.18–2.50 
 Present 23 25.6 67 74.4      
CT completed 
 No 201 47.1 226 52.9 .002d 1.47 1.14–1.89 1.25 1.08–1.44 
 Yes 268 37.7 443 62.3      
 NA/unknown/missing 19 46.3 22 53.7      
Amputations 
 Absent 475 42.6 641 57.4 .001 2.85 1.48–5.58 2.06 1.28–3.61 
 Present 13 20.6 50 79.4      
Bod Inj Sev (ISSmod)c 
 Minor/moderate 407 48.1 440 51.9 <.001 3.78 2.28–6.34 2.45 1.68–3.73 
 Severe or higher 22 19.6 90 80.4      
Immed auditory deficit 
 Present 277 52.0 256 48.0 <.001 2.23 1.75–2.85 1.59 1.38–1.83 
 Absent 211 32.7 435 67.3      
Current auditory deficit 
 Present 239 56.2 186 43.8 <.001d 2.87 2.17–3.81 1.82 1.55–2.14 
 Absent 148 30.9 331 69.1      
 Not applicable 101 36.7 174 63.3      
Planned disposition 
 Further treatment/care 347 42.5 470 57.5 .257 1.16 0.89–1.50 1.09 0.94–1.28 
 Return to duty 141 39.0 221 61.0      
ASD/PTSD (≥mild Sx) 
 Present n/a n/a n/a n/a n/a n/a n/a n/a n/a 
 Absent n/a n/a n/a n/a      
Days postinjuryc 
 3 or more months 308 59.3 211 40.7 <.001 3.89 3.02–5.01 2.17 1.89–2.51 
 <3 months 180 27.3 480 72.7      
Depression (NSI-20) 
 Moderate or higher 329 90.4 35 9.6 <.001 38.78 25.86–58.40 4.63 4.17–5.06 
 None or mild 159 19.5 656 80.5      
Depression (NSI-20) 
 Severe or higher 169 96.6 3.4 <.001 60.48 25.57–152.9 3.04 2.85–3.14 
 None, mild, or moderate 319 31.8 685 68.2      
 PCD/PTSD-High
 
PCD/PTSD-Low
 
p d    
 M SD M SD      
Age (in years) 27.5 7.3 26.8 7.0 .104 .10 – – – 
Days postinjury (NSI) 208.8 191.2 107.7 152.3 <.001 .60 – – – 
Bodily injury severity (ISSmod)a 5.2 5.4 8.0 7.9 <.001 .41 – – – 
Number of injury mechanisms 1.2 0.4 1.1 0.4 .339 .05 – – – 
Deployment numberb 1.7 0.9 1.7 1.0 .631 .06 – – – 
PCL-C total score 60.6 10.5 25.9 7.7 <.001 3.93 – – – 
NSI item 20 (Depression) 2.0 1.1 0.3 0.6 <.001 2.07 – – – 
 n n p OR 95% CI RR 95% CI 
Gender 
 Female 28 54.9 23 45.1 .045 1.77 0.97–3.22 1.35 0.98–1.70 
 Male 460 40.8 668 59.2      
Rank 
 Enlisted (E1–E9) 468 42.2 642 57.8 .031 1.79 1.02–3.16 1.46 1.01–2.23 
 Officer (O1–O7) + CW 20 29.0 49 71.0      
Branch of servicec 
 All other 447 43.3 585 56.7 <.001 7.57 5.30–10.84 4.72 3.49–6.48 
 Navy 41 27.9 106 72.1      
Mode of service 
 Reservist/Guard 237 48.1 256 51.9 <.001 1.60 1.26–2.04 1.31 1.14–1.51 
 Regular 251 36.6 435 63.4      
Deployment numberc 
 First/second 348 43.8 447 56.2 .201d 1.27 0.87–1.85 1.15 0.92–1.47 
 Third or more 56 38.1 91 61.9      
 Missing/NA 84 35.4 153 64.6      
Operation woundedc 
 OIF/other GWOT 348 48.7 366 51.3 <.001 2.21 1.71–2.85 1.62 1.38–1.91 
 All other 140 30.1 325 69.9      
Type of operation 
 Combat zone 426 43.3 557 56.7 .001 1.65 1.18–2.32 1.37 1.10–1.73 
 Non-combat zone 62 31.6 134 68.4      
Mechanism of injury 
 Blast 337 42.9 449 57.1 .143 1.20 0.93–1.55 1.12 0.96–1.31 
 Non-blast 151 38.4 242 61.6      
Loss of consciousnessc 
 Present 271 43.4 354 56.6 .276d 1.15 0.89–1.49 1.09 0.93–1.27 
 Absent 165 40.0 248 60.0      
 Unknown/missing 52 36.9 89 63.1      
Posttraumatic amnesiac 
 Present 338 41.2 483 58.8 .874d 1.02 0.76–1.37 1.01 0.86–1.21 
 Absent 106 40.6 155 59.4      
 Unknown/missing 44 45.4 53 54.6      
TBI severityc 
 All other TBI 473 42.3 644 57.7 .005 2.30 1.23–4.36 1.75 1.14–2.92 
 Complicated MTBI 15 24.2 47 75.8      
Intracranial Abn 
 Absent and No CT/MRI 465 42.7 624 57.3 .002 2.17 1.30–3.65 1.67 1.18–2.50 
 Present 23 25.6 67 74.4      
CT completed 
 No 201 47.1 226 52.9 .002d 1.47 1.14–1.89 1.25 1.08–1.44 
 Yes 268 37.7 443 62.3      
 NA/unknown/missing 19 46.3 22 53.7      
Amputations 
 Absent 475 42.6 641 57.4 .001 2.85 1.48–5.58 2.06 1.28–3.61 
 Present 13 20.6 50 79.4      
Bod Inj Sev (ISSmod)c 
 Minor/moderate 407 48.1 440 51.9 <.001 3.78 2.28–6.34 2.45 1.68–3.73 
 Severe or higher 22 19.6 90 80.4      
Immed auditory deficit 
 Present 277 52.0 256 48.0 <.001 2.23 1.75–2.85 1.59 1.38–1.83 
 Absent 211 32.7 435 67.3      
Current auditory deficit 
 Present 239 56.2 186 43.8 <.001d 2.87 2.17–3.81 1.82 1.55–2.14 
 Absent 148 30.9 331 69.1      
 Not applicable 101 36.7 174 63.3      
Planned disposition 
 Further treatment/care 347 42.5 470 57.5 .257 1.16 0.89–1.50 1.09 0.94–1.28 
 Return to duty 141 39.0 221 61.0      
ASD/PTSD (≥mild Sx) 
 Present n/a n/a n/a n/a n/a n/a n/a n/a n/a 
 Absent n/a n/a n/a n/a      
Days postinjuryc 
 3 or more months 308 59.3 211 40.7 <.001 3.89 3.02–5.01 2.17 1.89–2.51 
 <3 months 180 27.3 480 72.7      
Depression (NSI-20) 
 Moderate or higher 329 90.4 35 9.6 <.001 38.78 25.86–58.40 4.63 4.17–5.06 
 None or mild 159 19.5 656 80.5      
Depression (NSI-20) 
 Severe or higher 169 96.6 3.4 <.001 60.48 25.57–152.9 3.04 2.85–3.14 
 None, mild, or moderate 319 31.8 685 68.2      

Notes: n = 1,179 (PCD/PTSD-High, n = 488; PCD/PTSD-Low, n = 691). ISSmod = modified Injury Severity Scale; PCL-C = PTSD Checklist-Civilian Version; NSI = Neurobehavioral Symptom Inventory; OIF = Operation Iraqi Freedom; OEF = Operation Enduring Freedom; GWOT = Global War on Terror; MTBI = mild traumatic brain injury; AOC = alteration of consciousness; TBI = traumatic brain injury; CT = computed tomography; MRI = magnetic resonance imaging.

an = 1,030 (PCD/PTSD-High, n = 439; PCD/PTSD-Low, n = 591).

bn = 942 (PCD/PTSD-High, n = 404; PCD/PTSD-Low, n = 538).

cThese data were derived from a larger number of categories that were collapsed together based on common percentages. These additional data are available on request.

dp-value generated by ignoring missing values.

For the categorical variables, being (i) female, (ii) serving in the military in the enlisted ranks (versus Officer or Chief Warrant officer); in the Army, Marine Corps, Air Force, or Coast Guard (versus Navy); or as a Reservist or National Guard (versus Regular Active Duty), and (iii) been injured while deployed in a combat zone, and in particular, while deployed during OIF and a military operation relating to the GWOT (versus OEF/non-combat) were associated with increased risk of PCD. In addition, the PCD/PTSD-High group was statistically more likely to (iv) be evaluated 3 or more months postinjury, (v) have a CT scan not ordered after injury, (vi) have the absence of intracranial abnormality, (vii) have had an auditory deficit at the time of evaluation and at the time of injury, (viii) have had no amputations, (ix) have sustained a minor/moderate bodily injury (versus a more severe bodily injury), and (x) have sustained a TBI that was classified as uncomplicated MTBI, equivocal MTBI, or moderate TBI (versus complicated MTBI) (range: p < .001 to p = .045; OR = 1.47–7.57; RR = 1.25–4.72). Of particular mention, the PCD/PTSD-High group was also statistically more likely to report the presence of depression as moderate or higher (p < .001, OR = 38.78, RR = 4.63) or severe or higher (p < .001, OR = 60.48, RR = 3.04).

Logistic regression analyses

To examine which factors provide the most unique contribution towards the prediction of postconcussion and PTSD symptom reporting, logistic regression analyses was undertaken to determine if those statistically significant and clinical meaningful factors (i.e., p < .05 and OR ≥ 2 or Cohen's d ≥ .30) identified in Table 3 could differentiate those participants in the PCD/PTSD-High and PCD/PTSD-Low groups. Variables that fit this initial criterion were as follows: (i) ISSmod score, (ii) amputations, (iii) ISSmod severity classification, (iv) NSI item 20-Depression, (v) moderate or higher depression classification, (vi) severe of higher depression classification, (vii) days tested postinjury, (viii) days tested postinjury category, (ix) branch of service, (x) operation where wounded, (xi) auditory deficit at the time of evaluation, (xii) auditory deficit at the time of injury, and (xiii) TBI severity classification. Due to the overlap of some variables, a final list of eight factors was selected: (i) ISSmod score (excluded amputations, ISSmod severity classification), (ii) NSI item 20-Depression (excluded moderate or higher depression classification, severe of higher depression classification), (iii) days tested postinjury (excluded days tested postinjury category), (iv) branch of service, (v) operation where wounded, (vi) auditory deficit at the time of evaluation, (vii) auditory deficit at the time of injury, and (viii) TBI severity classification. All categorical variables were dummy coded to reflect the presence/absence (1/0) of the target risk factor: i.e., branch of service (not Navy), military operation where wounded (OIF/GWOT), auditory deficit at time of evaluation (present), auditory deficit at time of injury (present), and TBI severity (not complicated TBI).

For the logistic regression analysis, all eight factors were entered simultaneously as the dependent variables and group membership as the independent variable. Of the eight factors entered, five factors were significant predictors of group membership (i.e., days postinjury [p < .001], current auditory deficit [p = .001], ISSmod [p < .001], military operation where wounded [p = .037], and NSI item 20-Depression [p < .001]), accounting for 65.6% of the variance (Nagelkerke R2; p < .001). Overall, 84.9% of participants were correctly classified using this criterion (78.1% PCD/PTSD-High; 89.7% PCD/PTSD-Low). When this analysis was repeated by including only the five significant factors, the results were virtually identical (p < .001, Nagelkerke R2 = 65.4%; Classification accuracy: 78.3% PCD/PTSD-High; 89.9% PCD/PTSD-Low).

A series of five exploratory logistic regression analyses was undertaken using each of the five factors separately as the dependent variable and group membership as the independent variable. All five models were significant predictors of group membership (all p < .001). The highest classification rates were found when using depression (67.4% PCD/PTSD-High; 94.9% PCD/PTSD-Low; R2 = 60.0%), followed by current auditory deficit (49.0% PCD/PTSD-High; 73.1% PCD/PTSD-Low; R2 = 6.7%), days postinjury (33.2% PCD/PTSD-High; 86.1% PCD/PTSD-Low; R2 = 10.4%), ISSmod scores (24.0% PCD/PTSD-High; 81.9% PCD/PTSD-Low; R2 = 5.7%), and military operation when wounded (0% PCD/PTSD-High; 100% PCD/PTSD-Low; R2 = 4.6%). OR and RR values for the classification rates from all logistic regression analyses previously are presented in Table 4 (top half of table). High OR and RR values were found when combining all five factors together (OR = 31.97, RR = 7.73). However, equally high OR and RR values were found when using depression alone (OR = 38.78, RR = 13.31). Consistently, low OR and RR values were found when using all other factors individually (all ORs < 3.08; all RRs < 2.39).

Table 4.

Comparison of classification accuracy of selected factors to identify the PCD/PTSD-High versus PCD/PTSD-Low group

  PCD/PTSD-High
 
PCD/PTSD-Low
 
p OR 95% CI RR 95% CI 
n n 
Logistic regression analyses 
 Model: all 8 factorsa 
  Present 384 78.7 104 21.3 <.001 32.76 23.28–46.17 7.77 6.34–9.57 
  Absent 70 10.1 621 89.9      
 Model: only 5 of 8 factorsb 
  Present 382 78.3 106 21.7 <.001 31.97 22.75–45.01 7.73 6.30–9.52 
  Absent 70 10.1 621 89.9      
 Model: depression 
  Present 329 90.4 35 9.6 <.001 38.78 25.86–58.40 4.63 4.17–5.06 
  Absent 159 19.5 656 80.5      
 Model: days postinjury 
  Present 162 33.2 326 66.8 <.001 3.08 2.29–4.14 2.39 1.90–3.03 
  Absent 96 13.9 595 86.1      
 Model: current auditory deficit 
  Present 239 49.0 249 51.0 <.001 2.61 2.03–3.35 1.82 1.56–2.12 
  Absent 186 26.9 505 73.1      
 Model: ISSmod minor/moderate 
  Present 117 24.0 371 76.0 <.001 1.43 1.06–1.92 1.33 1.05–1.67 
  Absent 125 18.1 566 81.9      
 Model: wounded OEF/GWOT 
  Present 488 100 – – – – – 
  Absent 691 100      
Clinical algorithms 
 Dep (Mod + ) + 1 or more of 4 factorsc 
  Present 326 90.8 33 9.2 <.001 40.13 26.53–60.96 4.60 4.15–5.00 
  Absent 162 19.8 658 80.2      
 Dep (Mod+) + 2 or more of 4 factors 
  Present 287 93.8 19 6.2 <.001 50.50 30.26–85.20 4.07 3.75–4.32 
  Absent 201 23.0 672 77.0      
 Dep (Mod+) + 3 or more of 4 factors 
  Present 206 97.6 2.4 <.001 100.22 39.36–278.7 3.35 3.16–3.44 
  Absent 282 29.1 686 70.9      
 Dep (Mod+) + 4 of 4 factors 
  Present 71 100 <.001 – – 2.66 2.46–2.66 
  Absent 417 37.6 691 62.4      
  PCD/PTSD-High
 
PCD/PTSD-Low
 
p OR 95% CI RR 95% CI 
n n 
Logistic regression analyses 
 Model: all 8 factorsa 
  Present 384 78.7 104 21.3 <.001 32.76 23.28–46.17 7.77 6.34–9.57 
  Absent 70 10.1 621 89.9      
 Model: only 5 of 8 factorsb 
  Present 382 78.3 106 21.7 <.001 31.97 22.75–45.01 7.73 6.30–9.52 
  Absent 70 10.1 621 89.9      
 Model: depression 
  Present 329 90.4 35 9.6 <.001 38.78 25.86–58.40 4.63 4.17–5.06 
  Absent 159 19.5 656 80.5      
 Model: days postinjury 
  Present 162 33.2 326 66.8 <.001 3.08 2.29–4.14 2.39 1.90–3.03 
  Absent 96 13.9 595 86.1      
 Model: current auditory deficit 
  Present 239 49.0 249 51.0 <.001 2.61 2.03–3.35 1.82 1.56–2.12 
  Absent 186 26.9 505 73.1      
 Model: ISSmod minor/moderate 
  Present 117 24.0 371 76.0 <.001 1.43 1.06–1.92 1.33 1.05–1.67 
  Absent 125 18.1 566 81.9      
 Model: wounded OEF/GWOT 
  Present 488 100 – – – – – 
  Absent 691 100      
Clinical algorithms 
 Dep (Mod + ) + 1 or more of 4 factorsc 
  Present 326 90.8 33 9.2 <.001 40.13 26.53–60.96 4.60 4.15–5.00 
  Absent 162 19.8 658 80.2      
 Dep (Mod+) + 2 or more of 4 factors 
  Present 287 93.8 19 6.2 <.001 50.50 30.26–85.20 4.07 3.75–4.32 
  Absent 201 23.0 672 77.0      
 Dep (Mod+) + 3 or more of 4 factors 
  Present 206 97.6 2.4 <.001 100.22 39.36–278.7 3.35 3.16–3.44 
  Absent 282 29.1 686 70.9      
 Dep (Mod+) + 4 of 4 factors 
  Present 71 100 <.001 – – 2.66 2.46–2.66 
  Absent 417 37.6 691 62.4      

Notes: n = 1,179 (PCD/PTSD-High, n = 488; PCD/PTSD-Low, n = 691). Dep (Mod+) = endorsement of NSI Item 20 (Depression) at a moderate level or higher.

aFactors included in Model 1 = NSI Item 20 (Depression item), days tested postinjury, number of prior blasts, intracranial abnormality, immediate auditory deficit, current auditory deficit, ISSmod, operation where wounded.

bFactors included in Model 1 = NSI Item 20 (Depression item), days tested postinjury, current auditory deficit, ISSmod, operation where wounded.

cFactors include days tested postinjury, current auditory deficit, ISSmod, operation where wounded.

Clinical algorithms

Clinical algorithms using the five factors identified previously (i.e., depression, current auditory deficit, days postinjury, bodily injury severity, and military operation where wounded) were used to further determine if these “risk factors” could differentiate participants in the PCD/PTSD-High and PCD/PTSD-Low groups. Cutoff scores and factors were evaluated singularly, and in combination, using the following criterion as a risk factor for the presence of PCD/PTSD: (i) depression reported as moderate or higher in severity on item 20 of the NSI, (ii) bodily injury severity classified as minor/moderate by the ISSmod score, (iii) having sustained an injury during OIF or the GWOT, (iv) auditory deficit present at the time of evaluation, and (v) evaluated three or more months postinjury. Variables and cutoffs were selected based on their ability to discriminate between the PCD/PTSD-High and PCD/PTSD-Low groups from Table 3. Because depression accounted for the majority of variance in previous analyses, clinical algorithms were derived based on a combination of depression and one or more of the four remaining factors. OR and RR values for these algorithms are presented in Table 4 (bottom half of table).

The PCD/PTSD-High group was significantly more likely to report depression and the presence of at least one other risk factor, for all clinical algorithms evaluated (all p < .001). The highest classification rates were found when combining depression with “two or more” factors (OR = 50.50, RR = 4.07), followed by “one or more” factors (OR = 40.13, RR = 4.60). Note that there was a very high OR when combining depression with “three or more” factors (OR = 100.22, RR = 3.35). However, this value should also be viewed with caution due to the unacceptably wide 95% CI band (39.36–278.7) that makes this value meaningless.

Discussion

The purpose of this study was to identify risk factors of high postconcussion and posttraumatic stress symptom reporting in a large sample of U.S. military service members following mild-to-moderate TBI. There were four factors that were considered to be statistically and meaningfully related to postconcussion symptom endorsement: (i) low bodily injury severity, (ii) posttraumatic stress symptoms, (iii) depression, and (iv) being wounded during a military operation related to the GWOT. However, when examining these four variables in statistical and clinical prediction models, posttraumatic stress symptoms and depression symptoms were clearly most strongly associated with clinically elevated postconcussion symptom reporting. Although the presence of both depression (endorsed as moderate or higher) and posttraumatic stress symptoms (endorsed as mild or higher) resulted in the greatest risk of postconcussion symptom reporting (i.e., OR = 7.75. RR = 2.51), only a small percentage of people who reported clinically elevated levels of postconcussion symptoms actually met this criteria (16.3%). Of greater preference were the clinical algorithms that included criteria using (i) posttraumatic stress symptoms alone and (ii) depression or posttraumatic stress symptoms combined. Although there was a slight decrease in OR and RR values when using these algorithms, a high risk of elevated postconcussion symptom reporting remained when these factors were present (i.e., OR = 4.24, RR = 2.40 and OR = 4.84, RR = 2.65, respectively). In addition, there was an increased prevalence of those people who reported clinically elevated postconcussion symptoms who met these criteria (53.2% and 60.1%, respectively).

With regard to identifying risk factors of posttraumatic stress symptoms in military personnel with TBI, we could not achieve this goal as elegantly as desired. Ideally, we would have compared the asymptomatic control group (i.e., PCD/PTSD-Low) with those patients who reported posttraumatic stress symptoms in the absence of postconcussion symptoms (i.e., PTSD-High). However, the prevalence of posttraumatic stress symptom reporting alone was very small in this sample (3.8%, n = 60) and these comparisons were not feasible. As a suitable alternative, however, we compared the asymptomatic control group with those individuals who reported both posttraumatic stress and postconcussion symptoms (i.e., PCD/PTSD-High). As a general rule, we consider the vast majority of patients in the PCD/PTSD-High group to consist of individuals whose clinical presentation primarily manifests from posttraumatic stress-related symptomatology. The relation between posttraumatic stress and postconcussion symptom reporting has been reported by many researchers (Cooper et al., 2011; Hoge, et al., 2008; Pietrzak, Johnson, Goldstein, Malley, & Southwick, 2009; Polusny et al., 2011; Schneiderman et al., 2008). Logically, this relation is not surprising when we consider the large overlap of many posttraumatic stress and postconcussion symptoms. Although there are a large number of symptoms that are unique to PTSD (e.g., flashbacks, etc.), there are no clearly unique symptoms of PCD. Practically, this tends to result in a systematic, expectancy bias towards the endorsement of postconcussion-like symptoms regardless of diagnosis. For example, if a patient sustains a mild TBI and experiences “true” postconcussion symptoms, they will endorse many symptoms on a postconcussion checklist, but will not endorse those symptoms that are unique to PTSD on a PTSD checklist. As such, these patients will be flagged as endorsing symptoms consistent with PCD but not PTSD. On the other hand, if a patient has a diagnosis of PTSD, they will endorse many symptoms on a PTSD checklist, and will also likely endorse many symptoms on a postconcussion checklist due to the large number of overlapping and non-specific symptoms on a postconcussion checklist. As such, these patients will be flagged as endorsing symptoms consistent with PTSD and PCD. The data from our own sample support this tenet. Of the 488 patients who endorsed PTSD symptoms, 89.1% also endorsed PCD symptoms. In contrast, of the 849 patients who endorsed PCD symptoms, 57.5% also endorsed PTSD symptoms. Of course, there is a possibility that many patients with PCD may also have concurrent PTSD. However, endorsement of PTSD rarely occurred in the absence of concurrent PCD symptom endorsement.

With regard to risk factors of posttraumatic stress symptom reporting in this sample, there were eight broad factors that were considered to be statistically and meaningfully related to concurrent posttraumatic stress and postconcussion symptom endorsement. However, when examining these eight variables in statistical and clinical prediction models, only five variables were predictors of concurrent posttraumatic stress and postconcussion symptom endorsement: (i) low bodily injury severity, (ii) depression, (iii) a longer period of time when evaluated postinjury, (iv) being wounded during OIF or an operation related to the GWOT, and (v) reporting to experience an auditory deficit at the time of evaluation. That said, of these five factors, the presence of depression (endorsed as moderate or higher) clearly resulted in the greatest risk of endorsing concurrent posttraumatic stress and postconcussion symptoms at a clinically significant level (OR = 38.78, RR = 13.31; 7.2% false positives). Although there was an increase in some OR and RR values when combining depression with other factors, depression by itself was very highly predictive of concurrent posttraumatic stress and postconcussion symptoms and had lower false-positive rates than any other algorithm.

The results of this study prompt a number of discussion points. First, the strong relation between posttraumatic stress, depression, and postconcussion symptoms in this study are consistent with other studies in both military and civilian populations. Past studies have found that PTSD and depression largely explain the relationship between a history of mild TBI and postconcussion symptom reporting, along with other general health symptoms (Hoge, et al., 2008; Pietrzak et al., 2009; Polusny et al., 2011; Schneiderman et al., 2008). Cooper and colleagues (2011) found that mild TBI patients with high levels of posttraumatic stress symptoms reported significantly more postconcussion symptoms than those reporting low levels of posttraumatic stress symptoms. Brenner and colleagues (2010) found that those service members diagnosed with mild TBI alone or PTSD alone had greater postconcussion symptom reporting than those with neither diagnosis. A diagnosis of both mild TBI and PTSD was more strongly associated with postconcussion symptom reporting than either mild TBI alone or PTSD alone. In a sample of civilian mild TBI patients and non-brain injured trauma controls, acute traumatic stress symptoms reported within 14 days postinjury was a significant predictor of postconcussion symptom reporting at 3 months postinjury, regardless of the presence or absence of mild TBI. Moreover, PTSD symptom reporting at 3 months following injury was more strongly associated with postconcussion symptoms than acute traumatic stress, indicating that the severity of traumatic stress and postconcussion symptoms strengthened over time (Meares et al., 2011). The influence of depression on postconcussion symptom reporting is also well documented in civilian populations (Iverson, 2005; Lange et al., 2011).

Second, the relation between decreased bodily injury severity and increased concurrent posttraumatic stress/postconcussion symptom reporting is also consistent with recent studies. That is, more serious bodily injuries have been found to be associated with lower, not increased, posttraumatic stress and postconcussion symptom reporting in U.S. military service members (French et al., 2012; French et al., in press; Kennedy, Cullen, Amador, Huey, & Leal, 2010). In a recent series of studies, French and colleagues demonstrated an inverse severity–response relation between bodily injury severity and symptom reporting on the PCL-C and NSI in 137 military service members from the Walter Reed Army Medical Center (Washington, DC). Greater bodily injury severity was associated with lower scores on the NSI and PCL-C (French et al., 2012). In a follow-up study using a much larger sample of 579 U.S. military personnel from multiple military medical facilities, French and colleagues (in press) replicated these findings and further elucidated that this inverse relation was largely influenced by injuries to the extremities and the face. Hypothesized explanations to account for lower symptom reporting in those who are more severely injured included (i) underreporting of symptoms, (ii) increased peer support, (iii) disruption of fear conditioning due to acute morphine use, or (iv) delayed expression of symptoms.

Third, with regard to time tested following injury, participants who were tested more than 3 months postinjury were more likely to endorse clinically significant posttraumatic stress and postconcussion symptoms compared to those participants evaluated within the first 3 months. Given the known relation between postconcussion, posttraumatic stress, and depressive symptoms in a military population (Brenner et al., 2010; Cooper et al., 2011; Hoge, et al., 2008; Meares et al., 2011; Pietrzak et al., 2009; Polusny et al., 2011; Schneiderman et al., 2008), it is possible that these findings reflect, in part, the tendency for mental health problems to intensify with time (Hoge, et al., 2004; Marx et al., 2009; Milliken et al., 2007; Seal et al., 2008). For example, in a sample of service members returning from Iraq, Millikin and colleagues found that less mental health distress was reported by service members immediately upon return from deployment compared to 4–10 months later (Milliken et al., 2007). Despite this possibility, however, it is considered more likely that these results reflect a sample selection bias. Patients who were seen at military medical treatment facilities for a TBI evaluation many months following injury are typically symptomatic. They are referred to the hospital for this reason. As such, there would be very few people who are referred to the hospital due to a remote TBI who are not symptomatic. In contrast, most of those patients who are evaluated within the first few months postinjury are medically evacuated from combat theater and were treated at the hospital soon after injury. As such, some of these patients were highly symptomatic whereas others were not.

Fourth, with regard to the remaining identified risk factors, participants who reported experiencing auditory deficit at the time of evaluation, and who were wounded during OIF or other GWOT, were more likely to report clinically elevated concurrent posttraumatic stress and postconcussion symptoms compared with those that did not. For self-reported auditory deficits, the clinical implications of this findings, and how this might increase the likelihood of posttraumatic stress and postconcussion symptoms, is unclear. More likely than not, this finding is simply a proxy for the strong relation between depression, posttraumatic stress, and postconcussion symptoms. In our sample, higher rates of depression were found in those service members who experienced auditory deficits (p < .001). Although the effect sizes were only small-medium (d = .33 and .32), increased symptoms of depression in those individuals with self-reported auditory deficits likely accounts for this finding. It may however also be a marker of blast proximity. That is, those who were close to blast events were more likely to having hearing difficulties. This close proximity to an explosion may be more emotionally traumatic. Additionally, hearing difficulties are known to worsen social isolation and withdrawal (Ciorba, Bianchini, Pelucchi, & Pastore, 2012), possibly complicating emotional difficulties. With regard to the military operation at the time when wounded, it is likely that the increased number of deaths and wounded service members during OIF accounts for this finding. As of July 2013, there were a larger number of deaths and wounded service members per year during OIF (deaths = 505; wounded = 3,649) compared with OEF (deaths = 191, wounded = 1,613) (Department of Defense, 2013) (Calculated based on the reported total number of deaths and wounded service members during OIF (4,422 and 31,927) and OEF (2,245 and 18,957)). Exposure to combat situations, witnessing emotionally traumatic events, and being wounded during combat has been shown to increase vulnerability to the development of PTSD and other mental health problems and service use in returning OEF and OIF service members (Hoge, et al., 2004; Lapierre et al., 2007; Sareen et al., 2007). In a sample of service members tested pre- and post-deployment to Iraq, deployment stressors and combat severity were associated with PTSD symptoms when compared with non-deployed service members (Vasterling et al., 2010).

This study has several methodological limitations. First, this was a sample of convenience. Although we evaluated the influence of multiple factors on posttraumatic stress and postconcussion symptom reporting, we were restricted to the factors that were available in the database. There are other known factors (Iverson, Silverberg, Lange, & Zasler, 2012) that could not be included here (e.g., social-psychological factors such as symptom attribution, diagnosis threat, and good-old-days bias). Of particular mention is the absence of variables to evaluate poor effort or symptom exaggeration in this sample, or information regarding compensation seeking status. In civilians, compensation seeking is common in patients who report persisting symptoms after mild TBI (Ardolf, Denney, & Houston, 2007; Mittenberg, Patton, Canyock, & Condit, 2002). In previous research by Lange and colleagues (2013), symptom exaggeration and poor effort were very strong risk factors for postconcussion symptom reporting in military service members. In that study, individuals who failed effort measures and/or measures of symptom exaggeration had a very high likelihood that they would meet DSM-IV-TR symptom criteria for PCD depending on the measures used (OR = 8.1–18.1; RR = 2.1–2.6). The relation between postconcussion symptom reporting and symptom exaggeration/poor effort is also consistent with previous research (Iverson, Lange, Brooks, & Rennison, 2010; Lange et al.,2010,, 2012; Tsanadis et al., 2008; Tsanadis, Montoya, Millis, Hanks, & Fichtenberg, 2007).

Second, we used one single item from the NSI to evaluate depression. The use of this single item is considered rudimentary and insufficient as a means for evaluating the complexities of the depressive disorder. Without doubt, a more comprehensive measure of depression would have been preferred. In addition, this predictor variable was not independent of group membership. This item was used as part of the criteria to classify our sample into PCD-Present versus PCD-Absent groups. However, this is just one of many items from the NSI that was used to classify PCD based on the DSM-IV-TR criteria and it did not have a meaningful influence on group membership. In our sample of 1,600 service members, 849 were classified as PCD-Present, and 751 as PCD-Absent. When these groups are reclassified by excluding the depression item, only 1% of the sample (n = 16) were reclassified from the PCD-Present category (n = 833) to the PCD-Absent category (n = 767). The difference is not considered meaningful or to have affected the results of the study. Despite the limitations of the depression variable, we considered this an important variable to include because of the strong relation with posttraumatic stress and postconcussion symptom reporting found in previous studies (Cooper et al., 2011; Hoge, et al., 2008; Pietrzak et al., 2009; Polusny et al., 2011; Schneiderman et al., 2008). Third, although not considered a limitation per se, it is important to acknowledge that the TBI severity classification system used here is not consistent with DoD clinical guidelines. As such, it is important for clinicians who use DoD clinical guidelines to view these results within the context of the classification system used in this study. For example, the “equivocal” and “uncomplicated” MTBI classifications used here are equivalent to the “mild TBI” DoD classification. Similarly, the “complicated MTBI” and “moderate TBI” classifications used here are equivalent to the “moderate TBI” DoD classification.

In sum, this study identified a number of “risk” factors for postconcussion and posttraumatic stress symptom reporting. However, caution must be provided when interpreting the clinical relevance of these factors. Although bodily injury severity, military operation where wounded, time evaluated postinjury, and the presence of auditory deficits after injury were considered to be statistically associated with postconcussion and/or posttraumatic stress symptom reporting, these “risk factors” were not considered to be clinically meaningful or reliable predictors of symptomatology. However, there was a very clear and clinically meaningful association between (i) depression and the prediction of posttraumatic stress symptoms and/or postconcussion symptoms and (ii) posttraumatic stress symptoms and the prediction of postconcussion symptoms. There are many factors that can account for postconcussion symptom reporting. TBI severity was not one of these factors. Clinicians evaluating individuals who have been exposed to combat and report emotional or physical symptoms should be aware of the complex interplay between bodily injury, exposure to emotionally traumatic events, and other factors in the expression and maintenance of symptoms.

Funding

This work was not supported by any grant funding.

Conflict of Interest

None declared.

Acknowledgments

Portions of these data were presented at the annual conference of the International Brain Injury Association, San Francisco, CA: March 2014.

The views expressed in this manuscript are those of the authors and do not reflect the official policy of the Department of the Navy, Department of the Army, Department of Defense, or the U.S. Government.

Some authors are employees of the U.S. Government and military service members. This work was prepared as part of their official duties. Title 17, USC, § 105 provides that “Copyright protection under this title is not available for any work of the United States Government.” Title 17, USC, § 101 defines a U.S. Government work as a work prepared by a military service member or employee of the U.S. Government as part of that person's official duties.

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