Abstract

This study compared the neuropsychological outcome in military personnel following mild-to-moderate traumatic brain injury (TBI). Participants were 83 service members divided into three injury severity groups: uncomplicated mild TBI (MTBI; n = 24), complicated MTBI (n = 17), and moderate TBI (n = 42). Participants were evaluated within 6 months following injury (73% within 3 months) using neurocognitive testing and the Personality Assessment Inventory (PAI). There were no significant differences between the three groups on the majority of neurocognitive measures. Similarly, there were no significant differences between the three groups on the majority of PAI clinical scales (all p > .05), with the exception of two scales. The uncomplicated MTBI group had significantly higher scores on the Anxiety-Related Disorders and Aggression scales compared with the complicated MTBI group, but not the moderate TBI group. Overall, these results suggest that within the first 6 months post injury, there were few detectable differences in the neuropsychological outcome following uncomplicated MTBI, complicated MTBI, or moderate TBI in this military sample.

Introduction

Traumatic brain injuries (TBIs) occur on a broad spectrum of severity ranging from very mild to catastrophic injuries. Although there are no universally accepted classification criteria, closed TBI is traditionally categorized into three severity ranges (i.e., mild, moderate, and severe) based on Glasgow Coma Scale (GCS) scores, duration of loss of consciousness (LOC), and duration of post-traumatic amnesia (PTA) (Carroll, Cassidy, Holm, Kraus, & Coronado, 2004; Mild Traumatic Brain Injury Committee of the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine, 1993; National Center for Injury Prevention and Control, 2003). A commonly used, though not universally agreed upon, system for classifying TBI severity is as follows: (a) Mild traumatic brain injury (MTBI): GCS = 13–15, LOC < 30 min, and PTA < 24 h (all three criteria must be met); (b) Moderate TBI: GCS = 9–12, LOC = 30 min to 24 h, and/or PTA = 1–7 days (any one criteria); and (c) Severe TBI: GCS = 3–8, LOC > 24 h, and/or PTA > 7 days (any one criteria; Iverson & Lange, 2011).

MTBI occurs on a broad spectrum. For example, it is important to note that there is a substantial minority of patients (7%–39%) who present to the emergency department following MTBI who have day-of-injury intracranial abnormalities detected on a computed tomography (CT) scan (e.g., edema, hematoma, or contusion; Borg et al., 2004; French & Dublin, 1977; Iverson, Lovell, Smith, & Franzen, 2000; Jeret et al., 1993; Levin, Williams, Eisenberg, High, & Guinto, 1992; Livingston, Loder, Koziol, & Hunt, 1991; Tellier et al., 1999; Thiruppathy & Muthukumar, 2004). As such, patients classified as sustaining an MTBI using mainstream criteria can theoretically range from those individuals who have sustained a brief alteration of consciousness (e.g., PTA < 1 min) to those who have experienced prolonged alteration in consciousness (e.g., LOC = 10min, PTA = 20 h) and a clearly detectable and significant intracranial abnormality (e.g., subdural hematoma).

The importance of the distinction between those patients with the presence/absence of intracranial abnormality in the MTBI range was made by Williams, Levin, and Eisenberg (1990) who used the terms “complicated” MTBI and “uncomplicated” MTBI to describe these two groups. A complicated MTBI was characterized by injury severity criteria in the mild range (e.g., GCS = 13–15, LOC < 30 min, and PTA < 24 h) and the presence of a visible intracranial abnormality (e.g., edema, hematoma, or contusion) or depressed skull fracture on day-of-injury CT scan (Iverson & Lange, 2011; Iverson, Lange, Gaetz, & Zasler, 2007). An uncomplicated MTBI was characterized by the absence of intracranial abnormalities (or depressed skull fracture), with all other severity criteria in the mild range (Iverson & Lange, 2011; Iverson et al., 2007). In a sample of patients with mild-to-moderate TBIs, Williams and colleagues (1990) found that patients with complicated MTBIs (intracranial abnormality or depressed skull fracture) were more likely to have persistent cognitive and psychological symptoms at 6 months post injury compared with uncomplicated MTBI, and their recovery pattern was more similar to the patients who had sustained a moderate TBI.

Since then, other researchers have made similar comparisons with mixed results. Some studies have reported that patients with complicated MTBIs perform worse on neuropsychological measures and report worse outcomes in the initial days (Kurca, Sivák, & Kucera, 2006), weeks (Borgaro, Prigatano, Kwasnica, & Rexer, 2003; Iverson, Franzen, & Lovell, 1999; Lange, Iverson, Zakrzewski, Ethel-King, & Franzen, 2005), months (van der Naalt, Hew, van Zomeren, Sluiter, & Minderhoud, 1999; Wilson, Hadley, Scott, & Harper, 1996), and years (Temkin, Machamer, & Dikmen, 2003) post injury compared with uncomplicated MTBI. However, other studies report little to no differences on neuropsychological testing between patients with complicated versus uncomplicated MTBI when tested within the first few hours (Hughes et al., 2004; Sadowski-Cron et al., 2006), 2–3 weeks (de Guise et al., 2010), and up to 40 months post injury (Hanlon, Demery, Martinovich, & Kelly, 1999; Hoffman & Harrison, 2009). McCauley, Boake, Levin, Contant, and Song (2001) reported that CT abnormalities were not associated with increased risk for the postconcussion syndrome at 3 months post injury. In contrast, de Guise and colleagues (2010) found that patients with uncomplicated MTBIs reported more postconcussion symptoms than patients with complicated MTBIs 2–3 weeks post injury. In another study, Sadowski-Cron and colleagues (2006) found no differences in cognitive functioning between patients with and without intracranial injuries tested within the first 2 h of admission; however, more subjective headache and memory complaints were reported by patients with intracranial injuries during a 1-year telephone follow-up interview.

In a series of studies by Iverson and colleagues, Iverson (2006) compared the performance of 50 patients with complicated MTBIs and 50 patients with uncomplicated MTBIs on neuropsychological measures, assessed within 2 weeks post injury. The patients were carefully matched on age, education, gender, and mechanism of injury. Patients with complicated MTBIs performed worse than those with uncomplicated MTBI on approximately half of the measures. The effect sizes ranged from small to medium. In a replication study, Lange, Iverson, and Franzen (2009) assessed patients within a week post injury who were carefully matched on age, education, gender, ethnicity, mechanism of injury, and days assessed post injury. Patients with complicated MTBIs performed worse than the uncomplicated MTBI on several measures. The effect sizes ranged from small to medium-large. In a recent study of patients enrolled from an emergency department in Finland, Iverson and colleagues (2012) reported that there was a significant difference in time to return to work. The patients with uncomplicated MTBIs had a median of 6.0 days (range = 0–77) off work compared with a median of 36 days (range = 3–315) for the complicated MTBI group. There were no significant differences between groups on neuropsychological testing conducted at 3–4 weeks following injury. Moreover, there were no differences in the proportion of patients who met criteria for ICD-10 postconcussional disorder at 3–4 weeks post injury.

The United States Department of Defense (DoD) and Department of Veterans Affairs (VA) have adopted a classification system for TBI that varies somewhat from systems used in the past. The VA/DoD uses GCS, LOC, PTA (and “alteration of consciousness”) to classify mild, moderate, and severe TBI. Within the mild range, the use of GCS, LOC, and PTA criteria are similar to mainstream criteria (i.e., GCS = 13–15, LOC < 30 min, and PTA < 24 h). However, the VA/DoD classification system (Department of Veterans Affairs & Department of Defense, 2009) recommends classifying any patient with intracranial abnormality as having a “greater than mild injury” (page 16). As such, using VA/DoD criteria, a patient presenting with intracranial abnormalities on CT or MRI scan is considered to have a moderate TBI at minimum, when GCS, LOC, and PTA falls within the MTBI range.

To date, only a few studies have compared differences in neurocognitive and/or neurobehavioral outcomes between patients with uncomplicated MTBIs versus combined complicated MTBI and moderate TBI groups. Hartikainen and colleagues (2010) found no differences between patients with uncomplicated MTBIs and patients in the combined TBI group on an executive reaction time test or a postconcussion questionnaire, tested 6 months post injury. Goldstein, Levin, Goldman, Clark, and Altonen (2001) found that at 2 months post injury, patients in the combined group (complicated MTBI and moderate TBI) performed worse than patients with uncomplicated MTBIs on 7 of 10 cognitive measures, but not on mood. In a related study that applied more traditional criteria to define MTBI groups, Iverson and colleagues (1999) found that patients with uncomplicated MTBI performed better on a task of verbal fluency when compared with those patients following complicated MTBI or moderate TBI.

One common element missing from nearly all studies comparing uncomplicated and complicated MTBI is the inclusion of a moderate TBI group as originally used by Williams and colleagues. As such, the purpose of this study is to compare the neuropsychological outcome following uncomplicated MTBI, complicated MTBI, and moderate TBI in US military service members. It was hypothesized that there would be a linear relation between injury severity and neuropsychological outcome. That is, as injury severity increases (a) neurocognitive performance will decrease (uncomplicated MTBI > complicated MTBI > moderate TBI) and symptom endorsement would increase (moderate TBI > complicated MTBI > uncomplicated MTBI). It is further hypothesized that the neuropsychological outcome in patients following complicated MTBI would be more similar to those patients following moderate TBI, compared with uncomplicated MTBI.

Method

Participants

Participants were 85 patients who sustained an MTBI or moderate TBI and were evaluated at the Walter Reed Army Medical Center (WRAMC), Washington, DC, following medical evacuation from the combat theater for their injuries while deployed during Operation Iraqi Freedom, Operation Enduring Freedom, or other combat operations related to the Global War on Terror. As a general rule, patients were primarily medically evacuated for limb loss or systemic injuries, rather than TBI per se. The sample consisted of three groups categorized by TBI severity: (a) 25 uncomplicated MTBI, (b) 17 complicated MTBI, and (c) 42 moderate TBI (see below for more detail on classification criteria used). Descriptive statistics and injury severity characteristics are presented in Table 1.

Table 1.

Demographic and injury severity characteristics

  Uncomplicated MTBI
 
Complicated MTBI
 
Moderate TBI
 
p-value 
M SD M SD M SD 
Age 27.7 6.9 30.9 10.1 26.6 7.9 .184 
Months post injury 2.7 1.9 2.1 2.0 2.5 1.9 .609 
Estimated premorbid intellectual abilitya 104.5 6.9 106.2 5.3 102.9 6.0 .179 
 N Percent N Percent N Percent χ2 
Gender 
 Men 23 95.8 17 100 40 95.2 1.00b 
 Women 4.2 4.8  
Ethnicity 
 Caucasian 19 79.2 16 94.1 31 73.8 .264b 
 Other 20.8 5.9 11 26.2  
Education 
 GED/12 years 33.3 41.2 20 47.6 .538 
 13+ years 16 66.7 10 58.8 22 52.4  
Intracranial abnormality 
 Absent 24 100 15 35.7 <.001c 
 Present 17 100 15 35.7  
 No scan/missing information 12 28.6  
Loss of consciousness 
 “Present” 5.9 9.5 <.001c 
 <15 min 24 100 16 94.1 24 57.1  
 16–59 min 11.9  
 1–24 h 21.4  
Post-traumatic amnesia 
 “Present” 4.2 <.001c 
 <24 h 23 95.8 17 100 9.5  
 1–7 days 38 90.5  
Amputations 
 No 22 91.7 14 82.4 29 74.4 .583b 
 Yes 8.3 5.9 15.4  
 Missing information 11.8 7.7  
Mechanism of injury 
 Non-blast 14 58.3 47.1 20 51.3 .704 
 Blast 10 41.7 52.9 19 48.7  
Where wounded 
 OIF/OEF 21 87.5 12 70.6 26 63.4 .105b 
 Other GWOT 12.5 29.4 15 36.6  
  Uncomplicated MTBI
 
Complicated MTBI
 
Moderate TBI
 
p-value 
M SD M SD M SD 
Age 27.7 6.9 30.9 10.1 26.6 7.9 .184 
Months post injury 2.7 1.9 2.1 2.0 2.5 1.9 .609 
Estimated premorbid intellectual abilitya 104.5 6.9 106.2 5.3 102.9 6.0 .179 
 N Percent N Percent N Percent χ2 
Gender 
 Men 23 95.8 17 100 40 95.2 1.00b 
 Women 4.2 4.8  
Ethnicity 
 Caucasian 19 79.2 16 94.1 31 73.8 .264b 
 Other 20.8 5.9 11 26.2  
Education 
 GED/12 years 33.3 41.2 20 47.6 .538 
 13+ years 16 66.7 10 58.8 22 52.4  
Intracranial abnormality 
 Absent 24 100 15 35.7 <.001c 
 Present 17 100 15 35.7  
 No scan/missing information 12 28.6  
Loss of consciousness 
 “Present” 5.9 9.5 <.001c 
 <15 min 24 100 16 94.1 24 57.1  
 16–59 min 11.9  
 1–24 h 21.4  
Post-traumatic amnesia 
 “Present” 4.2 <.001c 
 <24 h 23 95.8 17 100 9.5  
 1–7 days 38 90.5  
Amputations 
 No 22 91.7 14 82.4 29 74.4 .583b 
 Yes 8.3 5.9 15.4  
 Missing information 11.8 7.7  
Mechanism of injury 
 Non-blast 14 58.3 47.1 20 51.3 .704 
 Blast 10 41.7 52.9 19 48.7  
Where wounded 
 OIF/OEF 21 87.5 12 70.6 26 63.4 .105b 
 Other GWOT 12.5 29.4 15 36.6  

Notes: N = 83 (24 uncomplicated MTBI, 17 complicated MTBI, and 42 moderate TBI). TBI = traumatic brain injury; MTBI = mild TBI; OIF = Operation Iraqi Freedom; OEF = Operation Enduring Freedom; GWOT = Global War on Terrorism. Same subscript reflects significant differences between groups (p < .05).

aEstimated premorbid Full-Scale Intelligence Quotient using the Wechsler test of adult reading demographics only equation.

bFisher's exact test.

cSome cells were collapsed to calculate the Fisher exact test using a 3 × 2 table.

Participant Selection

Participants were selected from a larger sample of 662 military service members who were evaluated at WRAMC between March 2002 and July 2008 following a suspected or confirmed TBI, and who had agreed to the use of their clinical data for research purposes. Patients were included in the study if the following criteria were met: (a) had sustained a closed TBI (n = 577, 87.2% of sample), (b) had completed a core neuropsychological test battery (n = 448, 67.7% of sample), (c) had been administered the Word Memory Test (n = 562, 84.9% of sample) and had scored above the recommended cutoff score for providing adequate effort (n = 406, 61.3% of sample), (d) had been administered the Personality Assessment Inventory (PAI) (n = 512, 77.3% of sample) and had a valid and interpretable profile (n = 443, 66.9% of sample), (e) had sufficient information available that could “confidently” classify severity of brain injury as uncomplicated MTBI (n = 131, 19.8% of sample), complicated MTBI (n = 44, 6.6% of sample), or moderate TBI (n = 151, 22.8% of sample (note: 107 Severe TBI; 229 Unclassified), and (f) had been assessed by the neuropsychology service between 2 weeks and 6 months of injury (n = 444, 67.1% of sample). The mean time tested post injury was 2.5 months (SD = 1.9; 72.9% tested between 2 weeks and 3 months; 27.1% tested between 4 and 6 months).

Diagnosis of TBI was based on a routine comprehensive clinical evaluation undertaken by medical/healthcare professionals at WRAMC. As part of the standard clinical pathway, all patients treated at WRAMC who are considered to be “at risk” for TBI undertake a TBI evaluation. A low threshold is purposely used to classify patients “at risk” for TBI. Typically, patients are considered “at risk” for TBI if they sustained an injury to any part of their body above the shoulders during a battle or non-battle-related event, or are injured in any way by an event such as a blast, assault, MVA, or fall. For the large majority of patients, these evaluations are completed by a physician's assistant who is trained to evaluate the presence of TBI. In some cases, evaluations are also completed by other healthcare professionals such as neuropsychologists, social workers, and nurses who are trained to evaluate TBI. Evaluations typically include (a) a patient interview, (b) a medical chart review including the in-theater medical records when available, (c) case conferencing, and (d) family interview and gathering of other collateral information (if available). Diagnosis and severity of TBI is based on the presence and duration of LOC, presence and duration of alteration of consciousness, Glasgow Coma Scale (GCS) scores (if available), presence and duration of PTA, and neuroradiological scan results. Self-reported symptoms are routinely obtained during the TBI evaluation but are not used for diagnostic or classification purposes.

For the purposes of this study, the classification of brain injury severity was based primarily on the duration of LOC, duration of PTA, and the presence/absence of intracranial abnormality identified by CT or MRI scans undertaken within the first few days and/or weeks following injury. GCS scores are often not available shortly after combat-related injuries and were not uniformly available for use. TBI injury severity was defined as follows: (a) uncomplicated MTBI: PTA < 24 h, LOC < 15 min, and the absence of intracranial abnormality; (b) complicated MTBI: PTA < 24 h, LOC < 15 min, and the presence of intracranial abnormality; and (c) moderate TBI: LOC = 16 min to 24 h, PTA 1–7 days, and the presence or absence of intracranial abnormality (or no neuroimaging information available). For the moderate TBI group, some patients did not have PTA and LOC that both fell within the moderate TBI criteria. In these circumstances, when the duration of LOC < 15 min (i.e., mild classification) and PTA > 24 h (i.e., moderate classification), the patient was classified as having sustained a moderate TBI. It was our preference to use an LOC criterion of <30 min to classify MTBI consistent with commonly used military and civilian diagnostic criteria (Carroll et al., 2004; Department of Veterans Affairs & Department of Defense, 2009; Mild Traumatic Brain Injury Committee of the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine, 1993). However, the available information regarding LOC was limited to categorical data that did not allow us to differentiate between LOC greater or less than 30 min (i.e., available data = LOC < 15 min and LOC 16–60 min).

The protocols under which these data were collected were approved by the Institutional Review Board of WRAMC, Washington, DC. This study was completed in accordance with the guidelines of the Declaration of Helsinki.

Measures and Procedures

Measures were selected from a larger neuropsychological test battery (approximately 6 h) designed to provide objective documentation of neurocognitive and psychological functioning. Measures of psychological functioning included the PAI (Morey, 1991). The PAI generates 4 validity scales, 18 clinical scales, and 31 clinical subscales. Measures of interest from the PAI included 14 of the 18 clinical scales (i.e., somatic complaints, anxiety, anxiety-related disorders, depression, mania, paranoia, schizophrenia, borderline features, antisocial features, alcohol problems, drug problems, Aggression, Suicidal Ideation, and Stress). Participants were not included if their T-scores exceeded the recommended cutoff on any of the four validity scales: Inconsistency (T > 72), Infrequency (T > 74), Negative Impression Management (T > 91), or Positive Impression Management (T > 68). For some analyses, clinical scale elevations were classified into dichotomous categories based on T-scores cutoff in the manual. For the clinical scales, 60T or higher was classified as “mild or higher,” and 70T of higher was classified as “moderate or higher.”

Neurocognitive measures included the (a) Trail Making Test (TMT; Reitan, 1992): Part A and Part B; (b) California Verbal Learning Test—2nd Edition (CVLT-II; Delis, Kramer, Kaplan, & Ober, 2000): Total Trials 1–4 and Long Delay Free Recall; (c) Conners' Continuous Performance Test—2nd Edition (CPT-II; Conners, 2002): Omissions and Commissions; and (d) selected subtests from the Wechsler Adult Intelligence Scale—Third Edition (Wechsler, 1997): Similarities, Letter-Number Sequencing, Digit Symbol-Coding, Block Design, and Matrix Reasoning. As part of the standard test battery, patients also completed the Wechsler Test of Adult Reading (The Psychological Corporation, 2001) to estimate premorbid intellectual ability, and the Word Memory Test (WMT; Green, 2003) to evaluate effort during testing. Patients were classified as having provided “poor effort” when their performance on the WMT fell below the cutoff scores recommended in the manual.

For all neurocognitive measures, raw scores were converted to standard scores (e.g., z-scores, T-scores, scaled scores) using the following published norms: (a) TMT Part A and B completion time normative data by Heaton, Miller, Taylor, and Grant (2004), (b) WAIS-III manual for selected subtests (Wechsler, 1987), (c) CVLT-II manual for total and delay scores (Delis et al., 2000), and (d) CPT-II computer-generated report for Omissions and Commissions (Conners, 2002). With the exception of the WAIS-III subtests, all scores are presented as T-scores (M = 50, SD = 10). The CVLT-II Long Delay Free Recall z-score was converted to a T-score. Scaled scores (M = 10, SD = 3) on the WAIS-III subtests were retained unmodified.

Results

Demographics and Injury Variables

Descriptive statistics of demographic and injury variables by group are presented in Table 1. It is acknowledged that the probability of Type 1 error increases when multiple statistical comparisons are made and a more conservative p-value of <.01 might be typically used here (or Bonferroni correction). However, the small sample size reduces statistical power and the application of a p-value of <.01 was considered too stringent. Thus, it was decided to apply a more liberal statistical approach by interpreting findings using p < .05.

There were no significant main effects for age (p = .184), months tested post injury (p = .609), estimated premorbid intellectual ability (p = .179), gender (p = .999), ethnicity (p = .264), education (p = .538), amputations (p = .583), mechanism of injury (p = .704), or geographical location of injury (p = .105). As expected, there were significant main effects for intracranial abnormality, duration of LOC, and duration of PTA (all p < .001). These group differences are a direct consequence of sample selection.

Tukey's post hoc comparisons (i.e., continuous variables) revealed no significant differences between groups on all variables. There was, however, a non-significant trend towards the complicated MTBI group having higher scores on estimated premorbid intellectual ability when compared with the moderate TBI group (p = .058, d = 0.56, medium effect size), but not the uncomplicated MTBI group (p > .05, d = 0.27, small effect size). Medium effect sizes were also found for age when comparing the (a) uncomplicated MTBI and complicated MTBI group (d = 0.40), and (b) moderate TBI and complicated TBI groups (d = 0.51).

Pairwise comparisons (using χ2 analyses or Fisher exact tests) for the remaining variables (i.e., categorical variables) revealed no significant differences (p > .05) for all comparisons with the exception of geographical location of injury. There was a significantly higher proportion (p = .036) of patients in the uncomplicated MTBI group (87.5%) who were injured while deployed during Operation Iraqi Freedom or Operation Enduring Freedom compared with the moderate TBI group (63.4%), but not the complicated MTBI group (70.6%). Although not statistically significant (p = .075), for ethnicity, 94.1% of patients in the complicated MTBI group who were Caucasian compared with 73.8% in the moderate TBI group (73.8%).

Neurocognitive Measures

Descriptive statistics, group comparisons, and effect sizes (Cohen, 1988) for the 11 cognitive measures, by group, are presented in Table 2. There were no significant main effects (ANOVA) for the majority of the measures (range: p = .056 to .988), with the exception of CVLT-II Delayed Free Recall (p = .017). Pairwise comparisons revealed that the complicated MTBI group performed significantly better on CVLT-II Delayed Free Recall compared with both the uncomplicated MTBI group (p < .05, d = 0.86, large effect size) and moderate TBI group (p < .05, d = 0.75, large effect size). The complicated MTBI group also performed significantly better on CPT-II Omissions compared with the moderate TBI group (p < .05, d = 0.74, large effect size). There were no other significant pairwise comparisons between groups for the remaining measures.

Table 2.

Descriptive statistics, group comparisons, and effect sizes by group: Neurocognitive measures

  1. Uncomplicated MTBI
 
2. Complicated MTBI
 
3. Moderate TBI
 
ANOVA
 
Cohen's effect sizes (d)a
 
M SD M SD M SD p-value Pairwise comparisons 1 versus 2 2 versus 3 1 versus 3 
WAIS-III Similarities 10.8 2.4 10.9 2.8 10.4 2.3 .725 — 0.05 0.20 0.16 
WAIS-III Letter-Number Sequencing 9.5 2.6 10.9 2.7 10.5 2.8 .210 — 0.54 0.17 0.36 
WAIS-III Digit Symbol-Coding 8.6 2.5 8.5 2.4 8.6 2.7 .988 — 0.02 0.04 0.02 
WAIS-III Block Design 11.8 3.1 11.9 2.9 11.2 2.7 .643 — 0.04 0.24 0.19 
WAIS-III Matrix Reasoning 11.7 2.8 12.1 2.3 11.9 2.6 .885 — 0.16 0.10 0.06 
CVLT-II Total 45.5 9.8 49.9 12.0 45.6 8.5 .255 — 0.42 0.46 0.02 
CVLT-II Long Delayed Free Recall 39.6 12.8 50.0 11.0 41.2 11.9 .017 2 > 1 and 3 0.86 0.75 0.13 
TMT Part A 48.7 11.5 48.9 9.6 48.7 7.7 .995 — 0.03 0.03 0.00 
TMT Part B 50.2 9.0 50.4 7.4 49.0 10.2 .806 — 0.02 0.16 0.13 
CPT-II Omissionsb 55.2 17.6 47.5 7.0 60.1 21.1 .056 2 < 3 0.59 0.74 0.25 
CPT-II Commissionsb 52.3 9.8 48.7 8.6 52.0 11.9 .516 — 0.38 0.30 0.02 
  1. Uncomplicated MTBI
 
2. Complicated MTBI
 
3. Moderate TBI
 
ANOVA
 
Cohen's effect sizes (d)a
 
M SD M SD M SD p-value Pairwise comparisons 1 versus 2 2 versus 3 1 versus 3 
WAIS-III Similarities 10.8 2.4 10.9 2.8 10.4 2.3 .725 — 0.05 0.20 0.16 
WAIS-III Letter-Number Sequencing 9.5 2.6 10.9 2.7 10.5 2.8 .210 — 0.54 0.17 0.36 
WAIS-III Digit Symbol-Coding 8.6 2.5 8.5 2.4 8.6 2.7 .988 — 0.02 0.04 0.02 
WAIS-III Block Design 11.8 3.1 11.9 2.9 11.2 2.7 .643 — 0.04 0.24 0.19 
WAIS-III Matrix Reasoning 11.7 2.8 12.1 2.3 11.9 2.6 .885 — 0.16 0.10 0.06 
CVLT-II Total 45.5 9.8 49.9 12.0 45.6 8.5 .255 — 0.42 0.46 0.02 
CVLT-II Long Delayed Free Recall 39.6 12.8 50.0 11.0 41.2 11.9 .017 2 > 1 and 3 0.86 0.75 0.13 
TMT Part A 48.7 11.5 48.9 9.6 48.7 7.7 .995 — 0.03 0.03 0.00 
TMT Part B 50.2 9.0 50.4 7.4 49.0 10.2 .806 — 0.02 0.16 0.13 
CPT-II Omissionsb 55.2 17.6 47.5 7.0 60.1 21.1 .056 2 < 3 0.59 0.74 0.25 
CPT-II Commissionsb 52.3 9.8 48.7 8.6 52.0 11.9 .516 — 0.38 0.30 0.02 

Notes: N = 83 (24 uncomplicated MTBI, 17 complicated MTBI, and 42 moderate TBI). TBI = traumatic brain injury; MTBI = mild TBI; WAIS-III = Wechsler Adult Intelligence Scale-III; CVLT-II = California Verbal Learning Test-II; TMT = Trail Making Test; CPT = Conner's Continuous Performance Test-II; ACT = Auditory Consonant Trigrams.

aCohen's effect sizes: Small (0.2), medium (0.5), and large (0.8).

bHigh T-scores indicate worse performance on this test.

Comparison of the prevalence of the number of low scores was undertaken by considering all 11 measures simultaneously. The cumulative percentages of the number of low scores (using <16th, <10th, and <5th percentile as cutoff scores) by group are presented in Table 3. Using χ2 analyses, there were no significant differences in the percentage of patients that had multiple low scores across groups, with the exception of two comparisons: (a) 45.2% of the moderate TBI group had 2 or more low scores <16th percentile compared with 17.6% of the complicated MTBI group (p < .05) and (b) 11.8% of the complicated MTBI group had 1 or more low scores < 5th percentile compared with 47.6% of the moderate TBI group and 54.8% of the uncomplicated MTBI group (both p < .05).

Table 3.

Number of low neurocognitive test scores by group

Number of low scoresa 1. Uncomplicated MTBI (Cum %) 2. Complicated MTBI (Cum %) 3. Moderate TBI (Cum %) Pairwise Comparison % difference
 
1 versus 2 3 versus 2 1 versus 3 
<16th percentile 
 6 or more 8.3 — — — 8.3 8.3 
 5 or more 8.3 — 2.4 — 8.3 2.4 5.9 
 4 or more 16.7 5.9 9.5 — 10.8 3.6 7.2 
 3 or more 20.8 5.9 21.4 — 14.9 15.5 −0.6 
 2 or more 29.2 17.6 45.2 3 > 2 11.6 27.6 −16.0 
 1 or more 62.5 52.9 76.2 — 9.6 23.3 −13.7 
 Zero low scores 100.0 100.0 100.0 — — — — 
<10th percentile 
 5 or more 4.2 — 2.4 — 4.2 2.4 1.8 
 4 or more 8.3 — 7.1 — 8.3 7.1 1.2 
 3 or more 12.5 5.9 11.9 — 6.6 6.0 0.6 
 2 or more 25.0 17.6 31.0 — 7.4 13.4 −6.0 
 1 or more 58.3 41.2 66.7 — 17.1 25.5 −8.4 
 Zero low scores 100.0 100.0 100.0 — — — — 
<5th percentile 
 5 or more 4.2 — — — 4.2 4.2 
 4 or more 4.2 — 2.4 — 4.2 2.4 1.8 
 3 or more 12.5 5.9 7.1 — 6.6 1.2 5.4 
 2 or more 16.7 5.9 21.4 — 10.8 15.5 −4.7 
 1 or more 45.8 11.8 47.6 1 and 3 > 2 34.0 35.8 −1.8 
 Zero low scores 100.0 100.0 100.0 — — — — 
Number of low scoresa 1. Uncomplicated MTBI (Cum %) 2. Complicated MTBI (Cum %) 3. Moderate TBI (Cum %) Pairwise Comparison % difference
 
1 versus 2 3 versus 2 1 versus 3 
<16th percentile 
 6 or more 8.3 — — — 8.3 8.3 
 5 or more 8.3 — 2.4 — 8.3 2.4 5.9 
 4 or more 16.7 5.9 9.5 — 10.8 3.6 7.2 
 3 or more 20.8 5.9 21.4 — 14.9 15.5 −0.6 
 2 or more 29.2 17.6 45.2 3 > 2 11.6 27.6 −16.0 
 1 or more 62.5 52.9 76.2 — 9.6 23.3 −13.7 
 Zero low scores 100.0 100.0 100.0 — — — — 
<10th percentile 
 5 or more 4.2 — 2.4 — 4.2 2.4 1.8 
 4 or more 8.3 — 7.1 — 8.3 7.1 1.2 
 3 or more 12.5 5.9 11.9 — 6.6 6.0 0.6 
 2 or more 25.0 17.6 31.0 — 7.4 13.4 −6.0 
 1 or more 58.3 41.2 66.7 — 17.1 25.5 −8.4 
 Zero low scores 100.0 100.0 100.0 — — — — 
<5th percentile 
 5 or more 4.2 — — — 4.2 4.2 
 4 or more 4.2 — 2.4 — 4.2 2.4 1.8 
 3 or more 12.5 5.9 7.1 — 6.6 1.2 5.4 
 2 or more 16.7 5.9 21.4 — 10.8 15.5 −4.7 
 1 or more 45.8 11.8 47.6 1 and 3 > 2 34.0 35.8 −1.8 
 Zero low scores 100.0 100.0 100.0 — — — — 

Notes: N = 83 (24 uncomplicated MTBI, 17 complicated MTBI, and 42 moderate TBI). TBI = traumatic brain injury; MTBI = mild TBI.

aA total of 11 were considered for these analyses.

Demographic and Neurocognitive Measures

Given the known influence of demographic and injury variables on neuropsychological performance, the influence of select variables on the neurocognitive measures were examined using Pearson correlation and ANCOVA. Variables were selected if they met the following criteria: (a) there was a substantial pairwise difference on the variable between any two groups (i.e., defined by p < .05 or d > 0.40) or a trend towards significance (i.e., p < .08) and (b) the variable was considered to have the potential for influencing the test performance. The following variables were selected for further analyses: age, ethnicity, and premorbid intellectual ability (but not geographical location of injury).

There were significant correlations found for (a) ethnicity with CPT-II Commissions (r = −.30, p = .006) and (b) estimated premorbid intellectual ability with Similarities (r = .33, p = .003), Block Design (r = .39, p < .001), CVLT Total (r = .22, p = .047), and CVLT-II Delayed Free Recall (r = .25, p = .024). Group comparisons using ANCOVA with estimated premorbid intellectual ability as a covariate revealed no significant main effects for all measures (range: p = .111 to p = .950) except CVLT-II Delayed Free Recall (p = .032). Pairwise comparisons revealed that the complicated MTBI group performed significantly better on this measure compared with both the uncomplicated MTBI group (p = .016) and moderate TBI group (p = .032) when controlling for the influence of premorbid intellectual ability.

Visual inspection of descriptive statistics and additional exploratory analyses were conducted on premorbid intellectual ability and ethnicity. Visual inspection of mean neurocognitive test scores and exploratory t-tests were conducted using ethnicity as the independent variable. There was not a systematic trend for minorities to perform more poorly than Caucasian. Exploratory bivariate correlations, within each TBI group, were conducted between estimated premorbid intelligence and neurocognitive test performance. Within the complicated MTBI group, the correlation between premorbid intelligence and the CVLT-II Delayed Free Recall score was r = .50 (p = .39).

Psychological Measures

Descriptive statistics, group comparisons, and Cohen's effect sizes for the 14 PAI clinical scales by group are presented in Table 4. There were no significant main effects (ANOVA) across groups for any measure (all p > .05). Exploratory pairwise comparisons revealed that the uncomplicated MTBI group had significantly higher scores on the Anxiety-Related Disorders (p < .05, d = 0.74 large effect size) and Aggression scales (p < .05, d = 0.72 large effect size), compared with the complicated MTBI group. A medium effect size between these groups was also noted on the Anxiety (p > .05, d = 0.58), Paranoia (p > .05, d = 0.47) and Alcohol Problems (p > .05, d = 0.46) scales. Other notable effect sizes were found when comparing the complicated MTBI and moderate TBI groups on the Anxiety (d = 0.38), Anxiety-Related disorders (d = 0.40), and the Antisocial Features scale (d = 0.39; moderate TBI > complicated MTBI for all scales); and between the uncomplicated MTBI and moderate TBI groups on the Aggression scale (d = 0.38; uncomplicated MTBI > moderate TBI).

Table 4.

Descriptive statistics, group comparisons, and effect sizes by group: PAI validity and clinical scales

  1. Uncomplicated MTBI
 
2. Complicated MTBI
 
3. Moderate TBI
 
ANOVA
 
Cohen's effect sizes (d)a
 
M SD M SD M SD p-value Pairwise comparison 1 versus 2 2 versus 3 1 versus 3 
Validity scales 
 Inconsistency 49.8 7.9 47.5 8.3 49.1 8.0 .662 — 0.28 0.20 0.08 
 Infrequency 50.6 6.5 49.8 8.8 51.4 8.2 .759 — 0.12 0.20 0.10 
 Negative Impression Management 53.1 9.9 50.8 11.0 49.9 7.4 .373 — 0.23 0.10 0.29 
 Positive Impression Management 50.3 8.9 52.8 11.1 52.4 9.2 .634 — 0.25 0.05 0.23 
Clinical scales 
 Somatic Complaints 58.6 10.2 56.4 10.5 55.8 10.3 .563 — 0.22 0.05 0.27 
 Anxiety 52.6 10.6 47.1 7.8 50.7 10.1 .213 — 0.58 0.38 0.19 
 Anxiety-Related Disorders 52.6 11.1 45.2 8.3 49.7 12.2 .122 1 > 2 0.74 0.40 0.25 
 Depression 55.8 10.8 57.0 15.9 54.5 11.7 .775 — 0.09 0.19 0.11 
 Mania 52.4 8.4 50.6 11.9 51.9 9.7 .836 — 0.19 0.13 0.05 
 Paranoia 56.7 10.2 51.8 10.2 53.5 8.2 .226 — 0.47 0.19 0.35 
 Schizophrenia 54.0 12.2 52.2 13.3 52.0 10.5 .782 — 0.14 0.02 0.18 
 Borderline Features 54.4 10.5 51.5 10.4 52.6 10.4 .659 — 0.28 0.10 0.17 
 Antisocial Features 54.9 10.8 54.5 7.6 58.4 10.9 .285 — 0.04 0.39 0.32 
 Alcohol Problems 48.2 6.7 51.8 9.1 49.2 7.5 .327 — 0.46 0.33 0.13 
 Drug Problems 47.1 5.1 48.9 5.6 49.0 7.3 .474 — 0.35 0.01 0.30 
 Aggression 57.9 9.7 50.5 11.0 54.0 11.0 .092 1 > 2 0.72 0.31 0.38 
 Suicide 47.8 6.6 47.5 6.3 46.7 5.0 .371 — 0.06 0.14 0.20 
 Stress 56.1 12.2 53.6 11.6 54.2 10.8 .749 — 0.20 0.05 0.17 
  1. Uncomplicated MTBI
 
2. Complicated MTBI
 
3. Moderate TBI
 
ANOVA
 
Cohen's effect sizes (d)a
 
M SD M SD M SD p-value Pairwise comparison 1 versus 2 2 versus 3 1 versus 3 
Validity scales 
 Inconsistency 49.8 7.9 47.5 8.3 49.1 8.0 .662 — 0.28 0.20 0.08 
 Infrequency 50.6 6.5 49.8 8.8 51.4 8.2 .759 — 0.12 0.20 0.10 
 Negative Impression Management 53.1 9.9 50.8 11.0 49.9 7.4 .373 — 0.23 0.10 0.29 
 Positive Impression Management 50.3 8.9 52.8 11.1 52.4 9.2 .634 — 0.25 0.05 0.23 
Clinical scales 
 Somatic Complaints 58.6 10.2 56.4 10.5 55.8 10.3 .563 — 0.22 0.05 0.27 
 Anxiety 52.6 10.6 47.1 7.8 50.7 10.1 .213 — 0.58 0.38 0.19 
 Anxiety-Related Disorders 52.6 11.1 45.2 8.3 49.7 12.2 .122 1 > 2 0.74 0.40 0.25 
 Depression 55.8 10.8 57.0 15.9 54.5 11.7 .775 — 0.09 0.19 0.11 
 Mania 52.4 8.4 50.6 11.9 51.9 9.7 .836 — 0.19 0.13 0.05 
 Paranoia 56.7 10.2 51.8 10.2 53.5 8.2 .226 — 0.47 0.19 0.35 
 Schizophrenia 54.0 12.2 52.2 13.3 52.0 10.5 .782 — 0.14 0.02 0.18 
 Borderline Features 54.4 10.5 51.5 10.4 52.6 10.4 .659 — 0.28 0.10 0.17 
 Antisocial Features 54.9 10.8 54.5 7.6 58.4 10.9 .285 — 0.04 0.39 0.32 
 Alcohol Problems 48.2 6.7 51.8 9.1 49.2 7.5 .327 — 0.46 0.33 0.13 
 Drug Problems 47.1 5.1 48.9 5.6 49.0 7.3 .474 — 0.35 0.01 0.30 
 Aggression 57.9 9.7 50.5 11.0 54.0 11.0 .092 1 > 2 0.72 0.31 0.38 
 Suicide 47.8 6.6 47.5 6.3 46.7 5.0 .371 — 0.06 0.14 0.20 
 Stress 56.1 12.2 53.6 11.6 54.2 10.8 .749 — 0.20 0.05 0.17 

Notes: N = 83 (24 uncomplicated MTBI, 17 complicated MTBI, and 42 moderate TBI). TBI = traumatic brain injury; MTBI = mild TBI.

aCohen's effect sizes: small (0.2), medium (0.5), and large (0.8). The PAI subscales were not available in the database.

The percentages of patients with elevated PAI scales “mild or greater” and “moderate or greater” in each group are presented in Table 5. Overall, there were no significant main effects for all PAI scales across the three groups. Exploratory pairwise comparisons (using χ2 analyses) for all scales revealed only two significant differences. The uncomplicated MTBI group had a significantly higher (p < .05) proportion of individuals who elevated the Anxiety-Related Disorders scale (33.3%) compared with the complicated MTBI group (5.9%). In addition, the uncomplicated MTBI group had a higher (p < .05) proportion of individuals who elevated the Paranoia scale (41.7%) compared with the moderate TBI group (16.7%). Although not statistically significant, other notable pairwise comparisons included mild or higher scale elevations on the Aggression scale between uncomplicated MTBI (45.8%) and complicated MTBI (23.5%) groups (22.3% difference); and the Antisocial features scale between the moderate TBI (50.0%) and complicated MTBI (29.4%) groups (20.6% difference).

Table 5.

Percentage of individuals with elevated PAI clinical scales by group

  1. Uncomplicated MTBI (%) 2. Complicated MTBI (%) 3. Moderate TBI (%) Pairwise Comparison % difference
 
1 versus 2 2 versus 3 1 versus 3 
Mild or highera 
 Somatic Complaints 33.3 47.1 28.6 — 13.8 18.5 −4.7 
 Anxiety 25.0 17.6 23.8 — −7.4 −6.2 −1.2 
 Anxiety-Related Disorders 33.3 5.9 19.0 1 > 2 −27.4 −13.1 −14.3 
 Depression 29.2 29.4 28.6 — 0.2 0.8 −0.6 
 Mania 16.7 29.4 28.6 — 12.7 0.8 11.9 
 Paranoia 41.7 29.4 16.7 1 > 3 −12.3 12.7 −25.0 
 Schizophrenia 20.8 35.3 26.2 — 14.5 9.1 5.4 
 Borderline Features 20.8 23.5 23.8 — 2.7 −0.3 3.0 
 Antisocial Features 33.3 29.4 50.0 — −3.9 −20.6 16.7 
 Alcohol Problems 8.3 23.5 7.1 — 15.2 16.4 −1.2 
 Drug Problems 11.8 9.5 — 11.8 2.3 9.5 
 Aggression 45.8 23.5 33.3 — −22.3 −9.8 −12.5 
 Suicide 8.3 5.9 2.4 — −2.4 3.5 −5.9 
 Stress 33.3 17.6 23.8 — −15.7 −6.2 −9.5 
Moderate or highera 
 Somatic Complaints 20.8 11.8 11.9 — −9.0 −0.1 −8.9 
 Anxiety 8.3 4.8 — −8.3 −4.8 −3.5 
 Anxiety-Related Disorders 8.3 11.9 — −8.3 −11.9 3.6 
 Depression 12.5 23.5 16.7 — 11 6.8 4.2 
 Mania 4.2 11.8 — 7.6 11.8 −4.2 
 Paranoia 8.3 5.9 4.8 — −2.4 1.1 −3.5 
 Schizophrenia 16.7 17.6 7.1 — 0.9 10.5 −9.6 
 Borderline Features 16.7 5.9 4.8 — −10.8 1.1 −11.9 
 Antisocial Features 12.5 11.8 21.4 — −0.7 −9.6 8.9 
 Alcohol Problems 5.9 2.4 — 5.9 3.5 2.4 
 Drug Problems — 
 Aggression 8.3 5.9 7.1 — −2.4 −1.2 −1.2 
 Suicide — 
 Stress 16.7 11.8 9.5 — −4.9 2.3 −7.2 
  1. Uncomplicated MTBI (%) 2. Complicated MTBI (%) 3. Moderate TBI (%) Pairwise Comparison % difference
 
1 versus 2 2 versus 3 1 versus 3 
Mild or highera 
 Somatic Complaints 33.3 47.1 28.6 — 13.8 18.5 −4.7 
 Anxiety 25.0 17.6 23.8 — −7.4 −6.2 −1.2 
 Anxiety-Related Disorders 33.3 5.9 19.0 1 > 2 −27.4 −13.1 −14.3 
 Depression 29.2 29.4 28.6 — 0.2 0.8 −0.6 
 Mania 16.7 29.4 28.6 — 12.7 0.8 11.9 
 Paranoia 41.7 29.4 16.7 1 > 3 −12.3 12.7 −25.0 
 Schizophrenia 20.8 35.3 26.2 — 14.5 9.1 5.4 
 Borderline Features 20.8 23.5 23.8 — 2.7 −0.3 3.0 
 Antisocial Features 33.3 29.4 50.0 — −3.9 −20.6 16.7 
 Alcohol Problems 8.3 23.5 7.1 — 15.2 16.4 −1.2 
 Drug Problems 11.8 9.5 — 11.8 2.3 9.5 
 Aggression 45.8 23.5 33.3 — −22.3 −9.8 −12.5 
 Suicide 8.3 5.9 2.4 — −2.4 3.5 −5.9 
 Stress 33.3 17.6 23.8 — −15.7 −6.2 −9.5 
Moderate or highera 
 Somatic Complaints 20.8 11.8 11.9 — −9.0 −0.1 −8.9 
 Anxiety 8.3 4.8 — −8.3 −4.8 −3.5 
 Anxiety-Related Disorders 8.3 11.9 — −8.3 −11.9 3.6 
 Depression 12.5 23.5 16.7 — 11 6.8 4.2 
 Mania 4.2 11.8 — 7.6 11.8 −4.2 
 Paranoia 8.3 5.9 4.8 — −2.4 1.1 −3.5 
 Schizophrenia 16.7 17.6 7.1 — 0.9 10.5 −9.6 
 Borderline Features 16.7 5.9 4.8 — −10.8 1.1 −11.9 
 Antisocial Features 12.5 11.8 21.4 — −0.7 −9.6 8.9 
 Alcohol Problems 5.9 2.4 — 5.9 3.5 2.4 
 Drug Problems — 
 Aggression 8.3 5.9 7.1 — −2.4 −1.2 −1.2 
 Suicide — 
 Stress 16.7 11.8 9.5 — −4.9 2.3 −7.2 

Notes: N = 83 (24 uncomplicated MTBI, 17 complicated MTBI, and 42 moderate TBI). TBI = traumatic brain injury; MTBI = mild TBI.

aFor the clinical scales, 60T or higher was classified as “mild or higher,” and 70T or higher was classified as “moderate or higher.”

The cumulative percentages of the number of elevated PAI scales endorsed as “mild or greater” in each group is presented in Table 6. Chi-square analyses revealed that there were no significant differences in the percentage of patients who had multiple elevated clinical scales across groups. The largest difference (18.5%) between groups was found between the uncomplicated MTBI and moderate TBI groups when using a criterion of 2 or more elevated scales; though this differences was not significant (p > .05: uncomplicated MTBI = 45.8%, moderate TBI = 64.3%).

Table 6.

Number of elevated PAI clinical scales by group

Number of scalesa 1. Uncomplicated MTBI (Cum %) 2. Complicated MTBI (Cum %) 3. Moderate TBI (Cum %) Pairwise Comparison % difference
 
1 versus 2 2 versus 3 1 versus 3 
Mild or higherb 
 12 or more 4.2 5.9 2.4 — 1.7 3.5 −1.8 
 11 or more 8.3 5.9 2.4 — −2.4 3.5 −5.9 
 10 or more 12.5 11.8 4.8 — −0.7 7.0 −7.7 
 9 or more 25.0 11.8 9.5 — −13.2 2.3 −15.5 
 8 or more 25.0 17.6 9.5 — −7.4 8.1 −15.5 
 7 or more 25.0 17.6 19.0 — −7.4 −1.4 −6 
 6 or more 25.0 17.6 23.8 — −7.4 −6.2 −1.2 
 5 or more 25.0 35.3 28.6 — 10.3 6.7 3.6 
 4 or more 37.5 41.2 33.3 — 3.7 7.9 −4.2 
 3 or more 45.8 41.2 52.4 — −4.6 −11.2 6.6 
 2 or more 45.8 58.8 64.3 — 13 −5.5 18.5 
 1 or more 70.8 64.7 71.4 — −6.1 −6.7 0.6 
 0 symptoms 100.0 100.0 100.0 — 
Moderate or higherb 
 8 or more 4.2 — 2.4 — −4.2 −2.4 −1.8 
 7 or more 4.2 — 2.4 — −4.2 −2.4 −1.8 
 6 or more 12.5 5.9 2.4 — −6.6 3.5 −10.1 
 5 or more 12.5 11.8 2.4 — −0.7 9.4 −10.1 
 4 or more 16.7 11.8 4.8 — −4.9 7.0 −11.9 
 3 or more 16.7 17.6 19.0 — 0.9 −1.4 2.3 
 2 or more 25.0 23.5 23.8 — −1.5 −0.3 −1.2 
 1 or more 41.7 41.2 45.2 — −0.5 −4.0 3.5 
 0 symptoms 100.0 100.0 100.0 — 
Number of scalesa 1. Uncomplicated MTBI (Cum %) 2. Complicated MTBI (Cum %) 3. Moderate TBI (Cum %) Pairwise Comparison % difference
 
1 versus 2 2 versus 3 1 versus 3 
Mild or higherb 
 12 or more 4.2 5.9 2.4 — 1.7 3.5 −1.8 
 11 or more 8.3 5.9 2.4 — −2.4 3.5 −5.9 
 10 or more 12.5 11.8 4.8 — −0.7 7.0 −7.7 
 9 or more 25.0 11.8 9.5 — −13.2 2.3 −15.5 
 8 or more 25.0 17.6 9.5 — −7.4 8.1 −15.5 
 7 or more 25.0 17.6 19.0 — −7.4 −1.4 −6 
 6 or more 25.0 17.6 23.8 — −7.4 −6.2 −1.2 
 5 or more 25.0 35.3 28.6 — 10.3 6.7 3.6 
 4 or more 37.5 41.2 33.3 — 3.7 7.9 −4.2 
 3 or more 45.8 41.2 52.4 — −4.6 −11.2 6.6 
 2 or more 45.8 58.8 64.3 — 13 −5.5 18.5 
 1 or more 70.8 64.7 71.4 — −6.1 −6.7 0.6 
 0 symptoms 100.0 100.0 100.0 — 
Moderate or higherb 
 8 or more 4.2 — 2.4 — −4.2 −2.4 −1.8 
 7 or more 4.2 — 2.4 — −4.2 −2.4 −1.8 
 6 or more 12.5 5.9 2.4 — −6.6 3.5 −10.1 
 5 or more 12.5 11.8 2.4 — −0.7 9.4 −10.1 
 4 or more 16.7 11.8 4.8 — −4.9 7.0 −11.9 
 3 or more 16.7 17.6 19.0 — 0.9 −1.4 2.3 
 2 or more 25.0 23.5 23.8 — −1.5 −0.3 −1.2 
 1 or more 41.7 41.2 45.2 — −0.5 −4.0 3.5 
 0 symptoms 100.0 100.0 100.0 — 

Notes: N = 83 (24 uncomplicated MTBI, 17 complicated MTBI, and 42 moderate TBI). TBI = traumatic brain injury; MTBI = mild TBI.

aThere are 14 PAI clinical scales (validity scales excluded).

bFor the clinical scales, 60T or higher was classified as “mild or higher,” and 70T of higher was classified as “moderate or higher.”

An algorithm was developed to examine psychological distress on four specific clinical scales: Depression, Anxiety, Anxiety-Related Disorders, and Aggression. Having two or more of these clinical scales elevated (i.e., 65T or higher) was considered a marker for significant psychological distress. The percentages of each group who scored in this range were as follows: uncomplicated mild = 20.8%, complicated mild = 11.5%, and moderate = 19.0%.

Psychological and Neurocognitive Measures

To explore the influence of personality variables on neurocognitive test performance, a series of exploratory ANCOVAs were undertaken by comparing the three groups on those cognitive variables (from Table 2) that had significant main effects (i.e., CVLT-II Delay) or that had substantial pairwise differences (defined by p < .05 or d > 0.40) between groups (i.e., CVLT-II Total, CPT-II Commissions, and WAIS-III Letter-Number Sequencing) using selected PAI scales as covariates. PAI scales were selected (from Table 4) if there were two or more substantial (i.e., d = 0.38 or higher) pairwise differences between groups (i.e., Anxiety, Anxiety-Related Disorders, and Aggression).

When statistically controlling for psychological variables using the three PAI scales separately, significant main effects remained for CVLT Delayed Free Recall when using the Anxiety (p = .029), Anxiety-Related Disorders (p = .033), and Aggression scales (p = .023) as a covariate. There were no significant main effects for the remaining measures. Pairwise comparisons revealed that the complicated MTBI group performed significantly better on CVLT-II Delayed Free Recall compared with both the uncomplicated MTBI group and moderate TBI group when using Anxiety, Anxiety-Related Disorders, and Aggression scales as covariates (range: p = .008 to p = .020). The complicated MTBI group also performed significantly better on CPT-II Omissions compared with the moderate TBI group when using Anxiety (p = .039), Anxiety-Related Disorders (p = .030), and Aggression scale (p = .018) as a covariate.

Secondary Analysis: Moderate TBI Group with Abnormal Imaging

Due to the lack of differences between the moderate TBI group and the two MTBI groups, we completed a series of secondary exploratory analyses using a redefined moderate TBI group. For this group, we included only those individuals with known abnormal CT scans. Of the original 42 participants in the moderate TBI group, only 15 were retained (i.e., 15 normal CT, 9 with no scan, and 3 with missing information).

For the neurocognitive measures, there were no significant main effects (ANOVA) for the majority of the test scores (range: p = .151 to .996) with the exception of CVLT-II Delayed Free Recall (p = .026). Select pairwise comparisons (i.e., moderate TBI group vs. the two MTBI groups only) revealed no significant differences on any measure (all p > .05). There were, however, a number of medium to medium-large effect sizes found between the complicated MTBI and moderate TBI groups for CVLT-II Total (d = 0.47), CVLT-II Delayed Free Recall (d = 0.49), TMT Part B (d = 0.40), and CPT-II Omissions (d = 0.67); and the uncomplicated MTBI and moderate TBI groups for Letter Number Sequencing (d = 0.54) and TMT Part B (d = 0.42).

For the psychological measures, there were no significant main effects for any measures (range: p = .053 to .805). Select pairwise comparisons revealed no significant differences on the majority of measures (all p > .05), with the exception of the Somatic Complaints scale (p < .05, d = 0.83, uncomplicated MTBI > moderate TBI). Although not significantly different, there were a number of medium to medium-large effect sizes found between the complicated MTBI and moderate TBI groups on the Somatic Complaints (d = 0.59), Antisocial Features (d = 0.62), and Aggression (d = 0.39) scales; and between the uncomplicated MTBI and moderate TBI groups on the Anxiety (d = 0.49), Anxiety-Related Disorders (d = 0.56), Paranoia (d = 0.48), Antisocial Features (d = 0.49), Alcohol Problem (d = 0.64), and Drug Problem (d = 0.55) scales.

Discussion

The purpose of this study was to compare cognitive and psychological outcomes following uncomplicated MTBI, complicated MTBI, and moderate TBI in US military service members. The hypotheses were twofold. First, it was hypothesized that there would be a linear relation between injury severity and neuropsychological outcome. As injury severity increased, neurocognitive performance would decrease (i.e., uncomplicated MTBI > complicated MTBI > moderate TBI) and symptom endorsement would increase (i.e., moderate TBI > complicated MTBI > uncomplicated MTBI). Secondly, it was hypothesized that the neuropsychological outcomes of patients following complicated MTBI would be more similar to those who had sustained a moderate TBI, compared with those who sustained an uncomplicated MTBI. Overall, the results do not support these hypotheses. There were very few differences between the groups on cognitive testing or on a diverse range of mental health and physical symptoms, as assessed by the PAI. When differences were present, they were not consistently in the direction predicted by the hypotheses.

The three groups were compared on a comprehensive psychological test, the PAI. As seen in Table 4, some of the groups had mildly elevated scores, relative to the general population (M = 50, SD = 10), on scales measuring physical symptoms, depression, paranoia, aggression, and stress. The groups, on the whole, did not have large elevations on these scales. As seen in Table 5, some of the groups had a substantial minority (e.g., >15%) of patients who had highly elevated scores (i.e., >T70), particularly on the Somatic Complaints, Depression, Schizophrenia (this scale includes the “Thought Disorder” subscale, which includes several items relating to cognitive functioning), Borderline Features (this scale includes an “Affective Instability” subscale), Antisocial Features (this scale includes a “Stimulus Seeking” subscale with questions relating to risk-taking and bold behavior), and Stress clinical scales. If we conceptualize significant distress as having two or more PAI clinical scales above a T score of 70, then approximately 25% of each group scored in this range (Table 6). If we conceptualize significant psychological distress as having two or more scores of T65 or higher on the Depression, Anxiety, Anxiety-Related Disorders, or Aggression scales, the percentages of each group who scored in this range were as follows: uncomplicated mild = 20.8%, complicated mild = 11.5%, and moderate = 19.0%. Given that most of these patients were medically evacuated from Iraq or Afghanistan 2–26 weeks prior, it is notable that 75% or more were not endorsing high levels of psychological distress on the PAI.

When the three groups were compared on the PAI, when differences emerged, the complicated MTBI group tended to endorse “fewer” symptoms than the uncomplicated MTBI group and the moderate TBI group. Effect sizes ranged from medium to large. In general, however, the differences between the three groups on psychological testing were small—and the groups appeared to be more similar than dissimilar on psychological outcome measures.

These findings are somewhat consistent with a recent study (de Guise et al., 2010) that found that an uncomplicated MTBI group reported more symptoms on the Rivermead Postconcussion Questionnaire (RPSQ), 2–3 weeks post injury, compared with a complicated MTBI group (d = 0.45, medium effect size). Symptoms that most differed between groups were headaches, nausea, depression, restlessness, frustration, memory, and attention. No differences, however, were found on the Beck Depression Inventory-Second Edition (BDI-II) or the Beck Anxiety Inventory (de Guise et al., 2010). Similarly, Iverson and colleagues (2012) found that patients who had sustained an uncomplicated MTBI reported more symptoms on the RPSQ and BDI-II 3–4 weeks post injury compared with those patients following complicated MTBI (BDI-II, d = 0.52; RPSQ, d = 0.43, both medium effect sizes; Note: p > .05). Thomas and Youngjohn (2009) found no differences between uncomplicated and complicated MTBI groups on the MMPI-2 or MMPI-2-RF scales, with the exception of one scale. The complicated MTBI group had higher scores on RC3 (Cynicism) compared with the uncomplicated MTBI group (d = 0.74, large effect size; note: statistical comparisons between these two groups were not reported by the authors. Effect sizes were calculated and interpreted here. All other effect sizes were d < 0.20).

Inconsistent with the hypotheses, the three groups performed similarly on neuropsychological testing. Without question, their performance was much more similar than it was dissimilar. There were only a small number of differences between the groups. Surprisingly, when differences did exist, the complicated MTBI group actually performed “better” than the uncomplicated MTBI group, as illustrated by the effect sizes in Table 2. These findings are both consistent and inconsistent with previous studies. Some previous studies found little to no differences between uncomplicated and complicated MTBI groups on the majority of neurocognitive measures (de Guise et al., 2010; Hanlon et al., 1999; Hoffman & Harrison, 2009; Hughes et al., 2004; Iverson, 2006; Iverson et al., 2012; Lange et al., 2009; McCauley et al., 2001; Sadowski-Cron et al., 2006), whereas other studies report that patients with complicated MTBIs perform worse on neurocognitive measures compared with uncomplicated MTBI patients (Borgaro et al., 2003; Iverson et al., 1999; Kurca et al., 2006; Lange et al., 2005; van der Naalt et al., 1999; Williams et al., 1990; Wilson et al., 1996). However, we note that the tendency for the complicated MTBI group to perform comparably or better than the uncomplicated MTBI group has also recently been reported by Iverson and colleagues (2012).

Several factors may explain why the complicated MTBI group performed comparable with, or better than, the uncomplicated MTBI group on neuropsychological testing. First, when examining the demographic and injury variables across the three groups (Table 1), the complicated MTBI group tended to have a number of small differences on a combination of dispositional/demographic variables that might contribute to slightly better cognitive test performance. For example, the complicated MTBI group had higher estimated premorbid intellectual ability (d = 0.27, small affect size) and a higher percentage of Caucasians that belonged to the group. It is unlikely, however, that the minority status influenced these results because this variable was analyzed as a covariate and the significant results remained. Moreover, the visual inspection of mean neurocognitive test scores and exploratory t-tests were conducted using ethnicity as the independent variable, and there was not a systematic trend for minorities to perform more poorly than Caucasians. It is possible, however, that there was a bias in the complicated MTBI group in that this group had slightly higher estimated premorbid intelligence. The level of intelligence is positively correlated with neuropsychological test performance. Notably, within the complicated MTBI group, the correlation between estimated premorbid intelligence and the CVLT-II Delayed Free Recall score was r = .50 (p = .39). Moreover, as seen in Table 2, the CVLT-II scores for the complicated MTBI group were close to the healthy population mean (i.e., M = 50, SD = 10), whereas the scores for the other two groups were below the mean. Therefore, the better performance on the CVLT-II in the complicated MTBI group might be an artifact driven by a higher level of intelligence in this group.

Second, when we consider the results from the PAI, the uncomplicated MTBI group tended to report more psychological distress compared with the complicated MTBI group. Psychological distress could have a negative influence on cognitive test performance, which may contribute to the somewhat lower scores in the uncomplicated MTBI group. However, when the neurocognitive test performance was compared by taking into account the influence of psychological distress on neurocognitive test performance using ANCOVA, the differences between these two groups remained. Therefore, it is unlikely that psychological distress contributed to these findings in a major way.

Finally, there may be some bias in the way subjects were distributed across the groups. That is, the groups that had neuropsychological testing may not be completely representative of the larger pool of patients in each severity group. This may be especially notable in the uncomplicated MTBI group. Because the subjects had consented to use “clinical” data for research purposes, we are limited to those subjects who were referred for complete neuropsychological examinations. In clinical practice at the hospital, individuals with intracranial abnormalities, or moderate TBIs, would generally be more likely to get testing than would someone with an uncomplicated MTBI, unless other clinical or administrative factors drove the referral for testing. In other words, these may be subjects with other bodily injuries or clinical presentations that warranted further testing, limiting the generalizability of that group. Relatedly, those with moderate TBI at the more severe end of the spectrum may have been transferred for intensive inpatient rehabilitation elsewhere (e.g., VA polytrauma rehabilitation center) before neuropsychological evaluation. We did examine the idea that the moderate group may have suffered moderate brain injuries at the milder end of that spectrum. Of the 42 patients in the moderate TBI group, 15 had no intracranial abnormality, 9 had no CT scan completed (reasons unknown), and three had missing information. Only 15 of the sample had the presence of intracranial abnormality (38%). However, when only those individuals with intracranial abnormality were included in the moderate TBI group, contrary to expectations, the lack of differences between the moderate TBI group and the two MTBI groups remained. Ironically, when we compare the results of the original moderate TBI group with the moderate TBI subgroup, the subgroup who had an intracranial abnormality actually performed “better” on neuropsychological testing than the larger more heterogeneous group.

It is possible, but unknowable, that psychological factors influenced the motivational behavior of some of these service members during neuropsychological testing. For example, individuals who have sustained an uncomplicated MTBI, who know their diagnosis and expect to have cognitive problems arising from this injury, might subtly underperform on testing (not poor effort, per se, but subtle underperformance). This social psychological phenomenon, conceptualized as “diagnosis threat,” has been reported in two studies with university students who have a history of head trauma (Suhr & Gunstad, 2002, 2005). Alternatively, some service members who are told that they have an abnormality visible on a CT or MRI scan might actually have increased motivation on neuropsychological testing because they realize how important it is to perform optimally on these tests. These possible psychological factors influencing motivation during testing are speculative.

This study has several limitations. First, patients were classified into uncomplicated and complicated MTBI groups based on intracranial abnormality detected using CT scans, MRI scans, or both. In addition, some of the CT/MRI scans were performed soon after injury, while others were performed weeks post injury. Past studies that have examined complicated and uncomplicated MTBI groups have typically classified patients based on day-of-injury CT scans. MRI is known to be more sensitive in detecting intracranial abnormality, especially farther from the point of injury (Bigler, 2005), and the use of MRI scans to define groups may have resulted in the creation of two different groups when compared with those groups defined by past studies. For example, in previous studies, a patient with a normal CT scan would be classified in the uncomplicated MTBI group. However, in the current study, it is possible that an individual with a normal CT scan may be included in the complicated MTBI group, rather than the uncomplicated MTBI group, based on an abnormal MRI scan. As such, the inclusion of this person in the complicated MTBI group will tend to decrease the overall injury severity of the group because of the inclusion of individuals with more subtle intracranial abnormality than can be detected by CT scans alone. Unfortunately, information regarding CT versus MRI scans was not available for the vast majority of patients in the sample.

Second, information pertaining to the type, size, location, or severity of intracranial abnormality was not recorded, limiting the information available to evaluate severity. Intracranial abnormalities vary considerably in type, size, and location, and lesion characteristics can impact neuropsychological functioning (Bigler, 2007). Third, different norming approaches were used to score the neurocognitive tests. For example, (a) TMT scores are generated using norms adjusted for age, gender, education, and ethnicity; (b) CVLT scores are generated using norms adjusted for age and gender; and (c) WAIS-III scores are generated using norms adjusted for age only. Nonetheless, it is doubtful whether the different norming approaches would have affected the results.

Fourth, as a general rule, this sample consisted of patients who were primarily medically evacuated for bodily injuries, rather than TBI per se. As such, evaluation of the effects of MTBI, versus other factors, is very difficult. Particularly relevant to this population, recent research has shown that co-occurring bodily injury influences symptom reporting and mental health comorbidity, such as posttraumatic stress disorder. Service members with MTBI and bodily injury tend to report fewer PTSD and postconcussion symptoms than MTBI alone, and there tends to be a linear relation between bodily injury severity and symptom reporting. As bodily injury severity increases, symptom reporting decreases (French et al., 2011; Kennedy, Cullen, Amador, Huey, & Leal, 2010; Lange et al., 2011). We attempted to control for bodily injury severity in this study by using categorical information regarding amputations. However, the use of this information is not considered adequate for this purpose. Ideally, bodily injury severity scores using the Abbreviated Injury Severity scale should be used for this purpose. Unfortunately, bodily injury severity scores were not available for this sample. Future research should consider including an assessment of the impact of bodily injury severity on neuropsychological testing and symptom reporting across MTBI groups.

Finally, the generalizability of these results to all MTBIs may be limited due to the lack of information available to classify injury severity. For the most part, we attempted to classify MTBI based on ACRM and WHO criteria (e.g., GCS 13–15 after 30 min, LOC < 30 min, and PTA < 24 h). However, we were not able to use GCS scores because these scores are often not available shortly after combat-related injuries. In addition, we were not able to strictly apply the LOC criterion consistent with ACRM/WHO criteria. The available information regarding LOC was limited to categorical data that did not allow us to differentiate between LOC greater or less than 30 min (i.e., available data = LOC < 15 min and LOC 16–60 min). As such, we elected to apply a cutoff score of LOC < 15 min to differentiate mild from moderate TBI. However, it is important to note that individuals classified as moderate TBI were required to have the duration of PTA of 24 h or more. As such, the possibility of misclassification of TBI severity is considered inconsequential and unlikely to affect the generalizability of these results.

In conclusion, these results suggest that the psychological and cognitive outcome of service members with uncomplicated MTBIs, complicated MTBIs, and moderate TBIs was similar. There was not a clear trend for service members with more severe injuries to have worse psychological or cognitive outcome. This is the first study comparing outcomes in military service members comprising these three groups, so replication and extension of these findings are needed. Future studies involving these three groups should include better measures of postconcussion symptoms and traumatic stress, quantify bodily injuries, and examine the type, size, and location of imaging abnormalities.

Conflict of Interest

None declared.

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Author notes

Portions of these data were presented at the American Academy of Clinical Neuropsychology annual conference, July 2011, Washington DC, USA. The views expressed in this article are those of the authors and do not reflect the official policy of the Department of Defense or U.S. Government.