Deployment Risk Factors and Postdeployment Health Profiles Associated With Traumatic Brain Injury in Heavy Drinking Veterans

Abstract

Along with post-traumatic stress disorder (PTSD), mild traumatic brain injury (mTBI) is considered one of the “signature wounds” of combat operations in Iraq (Operation Iraqi Freedom [OIF]) and Afghanistan (Operation Enduring Freedom [OEF]), but the role of mTBI in the clinical profiles of Veterans with other comorbid forms of postdeployment psychopathology is poorly understood. The current study explored the deployment risk and postdeployment health profiles of heavy drinking OIF and OEF Veterans as a function of mTBI. Sixty-nine heavy-drinking OIF/OEF Veterans were recruited through a Veterans’ Affairs Medical Center and completed questionnaires and structured interviews assessing war-zone experiences, postdeployment drinking patterns, and PTSD symptoms. Veterans with positive mTBI screens and confirmed mTBI diagnoses endorsed higher rates of combat experiences, including direct and indirect killing, and met criteria for PTSD at a higher rate than Veterans without a history of mTBI. Both PTSD and combat experiences independently predicted screening positive for mTBI, whereas only combat experiences predicted receiving a confirmed mTBI diagnosis. mTBI was not associated with any dimension of alcohol use. These results support a growing body of literature linking mTBI with PTSD.

INTRODUCTION

The type of combat experienced by Veterans of Operation Enduring Freedom (OEF) in Afghanistan and Operation Iraqi Freedom (OIF) is associated with elevated rates of head injuries. Weapons like improvised explosive devices (IEDs) and mines are responsible for a substantial proportion of head injuries sustained in combat,¹ and exposure to blasts or explosions is commonly linked to mild traumatic brain injuries (mTBIs).² Estimates of mTBI prevalence rates among OEF/OIF Veterans range from 15% to 19%.^2,3 Although controversial, researchers have proposed that exposure to blasts may result in an mTBI when changes in atmospheric pressure resulting from the blast-wave, or barotrauma, stretch or displace brain tissue or cause acute gas emboli.⁴ In other words, concussion-type injuries may result from experiences that did not involve blunt force head trauma. Nevertheless, critics of the argument that barotrauma can result in mTBI point out that, in many cases, secondary and tertiary blast injuries involving physical trauma cannot be ruled out, and little evidence exists in the way of clinical studies to support the proposed mechanisms linking blast exposure and TBI.⁵ Despite this debate, the Veterans Health Administration initiated a population screening initiative⁶ that accepts biomechanical causes of mTBI.

Beyond blast injuries, a number of other war-zone experiences may place Veterans at increased risk for mTBI. Although the majority of TBIs are believed to result from IED explosions, other common causes include blunt trauma, falls, and motor vehicle accidents.⁷ In a sample of British troops deployed to Iraq, Fear et al⁸ examined war-zone risk factors associated with postconcussive symptoms, including headaches, dizziness, irritability, and difficulty concentrating, and reported that these symptoms were related not only to proximity of blast exposure but also to psychosocial Stressors like aiding the wounded and neurobiological risk factors like exposure to depleted uranium. In other words, some persistent postconcussive symptoms do not seem to be uniquely related to physical injuries sustained in the war-zone. Furthermore, symptoms that may be attributed to mTBI⁹ overlap considerably with symptoms of post-traumatic stress disorder (PTSD). So, it may be difficult to determine whether certain combat-related symptoms are attributable to mTBI or PTSD.

Given that the injury mechanisms associated with mTBI are also likely to be events that would meet the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR)¹⁰ definition of a traumatic event, and hence could also result in PTSD symptoms, it is possible that postconcussive symptoms are exacerbated by or strongly related to PTSD. Recent studies suggest that between 26% and 44% of OEF/OIF Veterans with a history of mTBI also screen positive for PTSD,^2,11 and PTSD was one of the strongest predictors of postconcussive symptoms in a large survey of OEF/OIF Veterans that left combat theaters by September 2004.¹² Interpreting these relations and the high rates of diagnostic comorbidity between mTBI and PTSD is difficult, however, given that these disorders share several symptoms (e.g., irritability, difficulty concentrating)¹³ and can theoretically result from the same combat experiences.

The high degree of overlap between residual mTBI symptoms and PTSD has led some researchers to argue that persistent postconcussive symptoms and PTSD are essentially equivalent syndromes. In addition to the overlapping arousal symptoms of increased irritability and difficulty concentrating, mTBI and PTSD may each be characterized by symptoms like emotional numbing and amnesia as well as post-trauma intrusive imagery of traumatic experiences.¹⁴ Moreover, the neuroanatomical regions associated with persistent postconcussive symptoms are generally the same regions implicated in PTSD,¹⁵ and TBI-related biomechanical injuries to these brain regions may at least partially explain why persistent mTBI and PTSD symptom profiles so closely mirror each other.

An additional complication in interpreting diagnostic overlap is that individuals with TBI are at risk for substance misuse,¹⁶ and a few recent studies have attempted to explore whether mTBI is an independent risk factor for substance misuse. In a Veteran sample, postconcussive symptoms were related to heavy drinking,⁸ and evidence from parallel lines of research involving civilian samples with TBI suggests that these individuals experience increased impulsivity and impaired decision making, which could contribute to an increased likelihood of alcohol-related problems.¹⁷ The exact nature of the relation between mTBI and alcohol use among returning Veterans, however, is poorly understood. Carlson et al¹⁸ reported that OEF/OIF Veterans screening positive for mTBI had higher rates of substance use disorders than Veterans without positive mTBI screens. Likewise, Polusny et al¹⁹ reported that mTBI was associated with problematic drinking although this relation dissipated after controlling for PTSD symptoms.

Overall, the emerging literature on combat-related mTBI suggests a complex pattern of relations between mTBI, PTSD, and substance misuse. Veterans with mTBI and co-occurring PTSD and substance use disorders are likely a more clinically severe subset of Veterans, yet little is known about the war-zone experiences and drinking patterns associated with this profile. Moreover, it is unclear how specific routine mTBI screening measures are, particularly within highly comorbid samples. This issue is especially important in Veterans’ Affairs Medical Centers (VAMC) given the large number of Veterans seeking health care through this system and the efforts being made to screen all returning OEF/OIF Veterans for mTBI.⁶ Consequently, the current study aimed to explore differences across several measures of deployment risk factors and postdeployment health outcomes between Veterans screening positive or negative for mTBI on the Veterans Affairs (VA) TBI Clinical Reminder. Given that mTBI screening measures are likely to yield false-positive results and may not specifically detect mTBI-related sequelae,²⁰ we also conducted all analyses using mTBI diagnostic status as derived from VAMC medical records as the grouping variable since diagnostic grouping may be a more specific indicator of mTBI-related problems.

METHOD

Participants

Sixty-nine participants were recruited primarily through the Memphis VAMC. The sample is predominantly male (91.3%, n = 63) with a mean age of 32.23 years (standard deviation [SD] = 8.80). A majority of the sample is Caucasian (65.2%, n = 45) or African American (27.5%, n = 19). The number of OEF/OIF deployments Veterans reported ranged from 1 to 4 (mean [M] = 1.48, SD = 0.70), and Veterans reported spending an average of 14.82 months (SD = 8.56) in a combat zone. Veterans were eligible for participation if they obtained a score of 8 or higher on the Alcohol Use Disorders Identification Test (AUDIT).²¹ Veterans screened via telephone interview were eligible based on a total score of 4 or higher on the consumption items of the AUDIT (AUDIT-C).²² The average AUDIT score for the sample was 12.97 (SD = 6.07).

Measures

VA TBI Clinical Reminder

The VA TBI Clinical Reminder is a brief screen for mTBI administered to all OEF/OIF Veterans seeking health care through the VAMC.⁶ The screen asks an initial prompt question about whether the Veteran received a TBI diagnosis during an OEF or OIF deployment. Veterans with no previous self-reported history of TBI are then asked a series of four questions regarding mTBI-related events and symptoms. Questions are organized into four sections, including events associated with an increased risk of mTBI (e.g., blasts, vehicular accidents), symptoms in the immediate aftermath of the event (e.g., feeling dazed or confused, loss of consciousness), symptoms following the event (e.g., sleep problems, headaches), and current symptoms (e.g., sleep problems, headaches). Negative responses to all of the items in a given section result in a negative screen, whereas a positive screen requires affirmative responses to at least one item in each section. Veterans with a positive screen are referred for additional evaluation in a Polytrauma clinic to determine whether symptoms reported in the clinical reminder are likely the result of mTBI or other physical or psychological conditions, and the results of follow-up evaluations were reviewed to determine whether Veterans received a clinician-confirmed diagnosis of mTBI.

mTBI Diagnosis

Veterans were categorized as receiving a clinician-confirmed mTBI diagnosis in one of two ways. First, Veterans were coded as having a clinician-confirmed mTBI if the Polytrauma evaluation included a statement clearly indicating that the findings are consistent with a diagnosis of TBI (e.g., “Are the findings consistent with a diagnosis of TBI? [Yes/No]”). Second, we used an approach adopted in other studies¹⁶ where Veterans were coded as having a clinician-confirmed mTBI if the evaluating clinician at the time of the Polytrauma consult assigned the Veteran a TBI-related International Classification of Diseases-9 code. One Veteran was referred to a rehabilitation clinic following his Polytrauma evaluation and received a TBI-related International Classification of Diseases-9 code at that appointment and was subsequently coded as having a confirmed mTBI diagnosis. We used the definition of mTBI adopted by the American Congress of Rehabilitation Medicine (loss of consciousness less than 30 minutes or post-traumatic amnesia less than 24 hours following the TBI)²³ to determine whether Veterans with confirmed diagnoses met criteria for mTBI versus more severe TBIs. Information documented in the Polytrauma evaluations indicated that all Veterans with confirmed diagnoses sustained mTBIs. To assess interrater agreement, two trained coders collected a subset of the chart data, including both mTBI screening and Polytrauma evaluation results, and the coders demonstrated excellent interrater agreement (Cohen’s κ = 0.99, p < 0.01).

Deployment Risk and Resilience Inventory

War-zone stressors were assessed using three scales from the Deployment Risk and Resilience Inventory (DRRI).²⁴ One scale measuring combat experiences consists of 15 items assessing whether Veterans experienced different combat-related events during deployment. Events on the scale include encountering land mines and/or booby traps and being in a vehicle that was under fire. Responses to these items are made using dichotomous “yes” or “no” options. The scale assessing perceived threat consists of 15-items scored on a 5-point, Likert-type scale where 1 = Strongly disagree and 5 = Strongly agree. Questions on the scale include items such as “I thought I would never survive” and “I was concerned that my unit would be attacked by the enemy.” Another scale was included to assess perceived exposure to nuclear, biological, and chemical (NBC) agents in the war zone. This scale consists of 20 items scored using three response options: “yes,” “no,” and “don’t know.” This scale also includes two items assessing proximity to exploding shells or missiles. The DRRI has shown good psychometric properties in a sample of OIF Veterans,²⁵ and each scale in the current study demonstrated good internal consistency (α ranges from 0.84 to 0.89).

Drinker Inventory of Consequences

The Drinker Inventory of Consequences (DrInC)²⁶ is a 50-item measure that assesses five dimensions of alcohol-related problems, including physical, intrapersonal, interpersonal, social responsibility, and impulse control. In addition to assessing the lifetime occurrence of various alcohol-related problems, the DrInC also assesses the frequency of alcohol-related problems in the past 3 months. The DrInC demonstrated good reliability in the current sample (α = 0.94).

Timeline Follow-Back

The Timeline Follow-Back (TLFB)²⁷ is a semistructured method for assessing drinking patterns over the past month. The method involves showing participants a calendar covering the last 30 days and asking them to retrospectively report how many standard drinks they consumed each day as well as the amount of time spent drinking on that day. For the current study, the TLFB was used to derive indices of past month drinking including the number of drinking days, mean number of drinks per drinking day, total binge drinking days, and the total number of drinks during the past month. The measure has shown good reliability and validity.²⁷

Clinician-Administered PTSD Scale

The Clinician-Administered PTSD Scale (CAPS)²⁸ is a structured clinical interview consisting of 17 items that assess each of the PTSD symptoms defined in the DSM-IV-TR.¹⁰ Each item consists of two parts assessing the frequency and intensity of the symptom where frequency and intensity are measured on separate 5-point scales. Scores from the 17 items can be used to derive dichotomous diagnostic categories as well as a continuous measure of PTSD symptom severity.

Procedure

Data for the present investigation were collected as part of a brief alcohol intervention study. Only data collected at the baseline assessment appointment (before intervention) were included in the present analyses. Participants were screened primarily through Memphis VAMC programs, including an OEF/OIF combat clinic serving as a gateway for Veterans seeking VA health care services. The OEF/OIF combat clinic includes a shared medical appointment where Veterans receive information on VA services. The majority of Veterans enrolled in this project were approached by research staff during these shared appointments and subsequently completed screening packets at that time. Some Veterans were recruited via flyers posted throughout the medical center and distributed in VAMC clinics. The flyers provided a telephone number and Veterans who called that number were informed about the study and screened over the phone. Eligible Veterans who enrolled in the project completed an assessment session with a clinical psychology doctoral student who administered a series of structured clinical interviews and self-report questionnaires. All students were supervised by a licensed clinical psychologist. Chart reviews of participants’ medical files were conducted to collect health information for Veterans enrolled in the project. All procedures were approved by the University of Memphis and Memphis VAMC Internal Review Boards, and Veterans provided informed consent before participation.

RESULTS

Before running analyses, we checked the data for potential outliers and examined the distributional property assumptions of each variable for possible violations of the assumption of univariate normality. Severely skewed or kurtotic variables were corrected using log or square-root transformations. The only severely skewed or kurtotic (and corrected) variables were derived from the DrInC and TLFB.

In all, 65 Veterans received documented screening for mTBI using the VA TBI Clinical Reminder and 25 (38.5%) of these screened positive for mTBI. Records for one Veteran indicated a positive screen for mTBI although items endorsed on the screen were not recorded. Of the remaining 24 Veterans with positive screens, 3 (12.5%) screened positive by reporting that they received a TBI diagnosis during an OEF/OIF deployment and did not complete the remaining items. Twenty-one Veterans screened positive by endorsing at least one item on each of the four questions, and the most common mTBI-related experiences reported during deployment were blasts and explosions (n = 18, 85.7%), vehicular accidents or crashes (n = 15, 71.4%), and falls (n = 8, 38.1%). The most common symptoms reported immediately after experiencing an mTBI-related event were “feeling dazed, confused, or seeing stars” (n = 19, 90.5%), losing consciousness (n = 7, 33.3%), and not remembering the event (n = 5, 23.8%). In terms of problems after the event, most Veterans with a positive screen reported sleep problems (n = 15, 71.4%) along with headaches (n = 12, 57.1%), irritability (n = 13, 61.9%), memory problems (n=11, 52.4%), balance problems or dizziness (n = 9, 42.9%), or sensitivity to bright light (n = 7, 33.3%). Of these symptoms, sleep problems seemed to be the most persistent with most of these Veterans reporting sleep problems during the week before completing the screening (n = 16, 76.2%). Other problems reported within the week before completing the screening were irritability (n = 14, 66.7%), headaches (n = 11, 52.4%), and memory problems (n = 10, 47.6%), with equal rates of dizziness and sensitivity to bright light (n = 6, 28.6%). Twenty-one (84.0%) Veterans screening positive for mTBI ultimately completed a Polytrauma evaluation, and just over half of these Veterans (n = 13, 52.0%) were diagnosed with mTBI. This proportion represents 20.0% of 65 participants receiving mTBI screens.

Deployment Risk Profiles

In terms of combat experiences, Veterans with both positive screens and confirmed mTBI diagnoses tended to report more combat experiences than Veterans without a history of mTBI (see Table I). Using two items on the DRRI, a higher proportion of Veterans with positive mTBI screens reported being within 1 km of an exploding artillery shell (n = 20, 80.0%) than Veterans with negative screens (n = 21, 52.5%; χ²(2) = 7.02, p = 0.03). A nonsignificant trend emerged such that a larger proportion of Veterans with a confirmed mTBI diagnosis endorsed being within 1 km of an exploding artillery shell (n=11, 84.6%) than Veterans without a confirmed diagnosis (n = 30, 57.7%; χ²(2) = 5.77, p = 0.06). Although one Veteran who screened negative for mTBI did not respond to this item, a nonsignificant trend emerged such that a higher proportion of Veterans with a positive mTBI screen endorsed being within 5 km of an exploding missile (n = 15, 60.0%) than Veterans with a negative screen (n = 16, 41.0%; χ²(2) = 5.51, p = 0.06). This trend held when comparing rates among Veterans with a confirmed mTBI (n = 7, 53.8%) and those without a confirmed mTBI (n = 24, 47.1%; χ²(2) = 5.46, p = 0.07).

TABLE I.

TBI Status and Rates of Combat Experiences

DRRI Combat Experiences Scale Items	TBI Screening			TBI Evaluation
	Positive (n = 25)	Negative (n = 40)	Statistic (df)	Confirmed (n =13)	Nonconfirmed (n = 52)	Statistic (df)
Went on Combat Patrols or Missions	96.0%	72.5%	χ2(1) = 5.64**	100%	76.9%	χ2(1) = 3.68*
Self or Unit Members Encountered Land or Water Mines and/or Booby Traps	84.0%	60.0%	χ2(1) = 4.16**	92.3%	63.5%	χ2(1) = 4.06**
Self or Unit Received Hostile Incoming Fire	96.0%	82.5%	χ2(1) = 2.60	100%	84.6%	χ2(1) = 2.28
Self or Unit Received “Friendly” Incoming Fire	40.0%	22.5%	χ2(1) = 2.28	38.5%	26.9%	χ2(1) = .67
Was in a Vehicle That was Under Fire	92.0%	45.0%	χ2(1) = 14.59***	92.3%	55.8%	χ2(1) = 5.96**
Self or Unit Members were Attacked by Terrorists or Civilians	92.0%	70.0%	χ2(1) = 4.41**	92.3%	75.0%	χ2(1) = 1.84
Part of a Land or Naval Artillery Unit That Fired on the Enemy	48.0%	17.5%	χ2(1) = 6.92***	46.2%	25.0%	χ2(1) = 2.25
Part of an Assault on Entrenched or Fortified Positions	76.0%	22.5%	χ2(1) = 17.96***	92.3%	30.8%	χ2(1) = 16.06***
Took Part in an Invasion That Involved Naval or Land Forcesa	50.0%	25.0%	χ2(1) = 4.16**	58.3%	28.8%	χ2(1) = 3.76*
Unit Engaged in Battle in Which it Suffered Casualtiesb	79.2%	35.0%	χ2(1) = 11.72***	84.6%	43.1%	χ2(1) = 7.14***
Witnessed a Unit or Ally Unit Member Being Seriously Wounded or Killed	88.0%	50.0%	χ2(1) = 9.72***	92.3%	57.7%	χ2(1) = 5.45**
Personally Witnessed Enemy Troops Being Seriously Wounded or Killeda	83.3%	32.5%	χ2(1) = 15.52***	91.7%	42.3%	χ2(1) = 9.51***
Wounded or Injured in Combatb	33.3%	2.5%	χ2(1)= 11.80***	46.2%	5.9%	χ2(1) = 13.90***
Fired Weapon at the Enemyb	87.5%	42.5%	χ2(1) = 12.59***	92.3%	51.0%	χ2(1) = 7.34***
Killed or Perceived Killing Someone in Combatc	65.0%	30.8%	χ2(1) = 6.34**	90.0%	32.7%	χ2(1) = 11.19***

^aBecause of missing data, sample sizes on this item include 24 Veterans screening positive for TBI and 12 Veterans with confirmed TBI.

^bBecause of missing data, sample sizes on this item include 24 Veterans screening positive for TBI and 51 Veterans with nonconfirmed TBI.

^cBecause of missing data, sample sizes on this item include 20 Veterans screening positive for TBI, 39 Veterans screening negative for TBI, 10 Veterans with confirmed TBI, and 49 Veterans with nonconfirmed TBI.

^*p < 0.10;

^**p < 0.05;

^***p < 0.01.

A series of logistic regression analyses examined the relative contributions of subjective and traumatic war-zone stressors in predicting mTBI screening and diagnostic status. Results are presented in Table II. No war-zone stressors emerged as statistically significant predictors of mTBI screening status, but the DRRI combat experiences scale emerged as a statistically significant predictor of receiving an mTBI diagnosis. Given that the DRRI combat experiences scale was the only statistically significant predictor of either screening positive for mTBI or receiving an mTBI diagnosis, two separate analyses were conducted with the DRRI combat experiences scale and CAPS total severity scores entered as predictors of mTBI screening and diagnostic status. Results of the logistic regression analyses revealed that both combat experiences and CAPS severity scores were unique predictors of screening positive for mTBI when both were simultaneously entered into the model without other war-zone stressors. In contrast, only the combat experiences scale emerged as a statistically significant predictor of receiving an mTBI diagnosis.

TABLE II.

Logistic Regression Analyses with War-zone and Mental Health Risk Factors Predicting TBI Status

Model and Predictors	β	SE	Wald Statistic	OR
TBI Screening Status
Model 1
Combat Experiences	0.20	0.11	3.20*	1.22
Perceived Threat	0.07	0.05	2.35	1.07
NBC Exposure	0.15	0.08	3.57*	1.16
Constant	−9.19	2.61	12.38***
Model 2
Combat Experiences	0.27	0.10	7.56***	1.31
CAPS Total Severity	0.04	0.02	7.15***	1.05
Constant	−5.27	1.25	17.71***
TBI Evaluation Status
Model 1
Combat Experiences	0.39	0.19	4.03**	1.48
Perceived Threat	−0.04	0.05	0.65	0.96
NBC Exposure	0.13	0.09	2.07	1.14
Constant	−6.37	2.51	6.43**
Model 2
Combat Experiences	0.38	0.16	5.69**	1.46
CAPS Total Severity	0.02	0.02	1.53	1.02
Constant	−6.35	1.79	12.57***

^*p < 0.10;

^**p < 0.05;

^***p < 0.01.

Rates of PTSD were compared between Veterans with and without a positive mTBI screen and Veterans with and without a confirmed mTBI diagnosis. Using the Frequency-1/Intensity-2 scoring rule on the CAPS²⁸ to derive PTSD diagnoses. Veterans with a positive mTBI screen were more likely to meet criteria for PTSD (n = 21, 84.0%) than Veterans with a negative screen (n = 18, 45.0%; χ²(1) = 9.75, p = 0.002). Veterans with confirmed mTBI diagnoses were also more likely to meet criteria for PTSD (n = 11, 84.6%) than Veterans without an mTBI diagnosis (n = 28, 53.8%; χ²(1) = 4.10, p = 0.04). Regarding PTSD severity scores derived from the CAPS, Veterans screening positive for mTBI had a higher mean CAPS score (M = 70.80, SD = 24.11) than Veterans with a negative screen (M = 41.80, SD = 21.45; t(63) = −5.06, p < 0.001). Veterans with a confirmed mTBI diagnosis also had a higher mean CAPS score (M = 72.00, SD = 23.78) than Veterans without a confirmed mTBI diagnosis (M = 48.19, SD = 25.11; t(63) = −3.09, p = 0.003).

TBI and Alcohol Use

In terms of alcohol use, Veterans with positive mTBI screens were compared to Veterans with negative mTBI screens on a number of alcohol-related consumption and consequences variables. Results are presented in Table III. No statistically significant differences emerged as a function of TBI status on any of the variables of interest. Veterans with confirmed mTBI diagnoses were compared to Veterans without a confirmed mTBI diagnosis and, similarly, no statistically significant differences emerged between these groups on any measure of alcohol use.

TABLE III.

TBI Status and Postdeployment Drinking Outcomes

	TBI Screening			TBI Evaluation
	Positive M(SD) (n = 25)	Negative M(SD) (n = 40)	Statistic (df)	Confirmed M(SD) (n = 13)	Nonconfirmed M(SD) (n = 52)	Statistic (df)
DrInC—Recent (Total)a	9.28 (9.32)	8.67 (7.99)	t(63) = 0.12	7.38 (8.31)	9.29 (8.53)	t(63) = 1.37
Physicala	2.16 (2.27)	2.40 (2.23)	t(63) = 0.66	1.77 (1.92)	2.44 (2.30)	t(63) = 1.27
Interpersonala	2.24 (2.59)	1.53 (1.62)	t(63) = −0.76	1.54 (1.90)	1.87 (2.11)	t(63) = 0.76
Intrapersonala	1.36 (2.18)	1.40 (1.85)	t(63) = 0.41	1.00 (1.47)	1.48 (2.07)	t(63) = 0.69
Impulse Controla	2.84 (3.16)	2.43 (2.44)	t(63) = −0.13	2.31 (3.25)	2.65 (2.60)	t(63) = 0.98
Social Responsibilityb	0.88 (1.45)	0.88 (1.22)	t(63) = 0.19	0.77 (1.09)	0.90 (1.36)	t(63) = 0.20
TLFB
Number of Drinking Daysa	9.88 (9.52)	11.10 (8.71)	t(63) = 0.70	7.69 (8.13)	11.37 (9.10)	t(63) = 1.68*
Drinks Per Drinking Daya	6.66 (4.15)	5.63 (3.14)	t(59) = −0.94	6.15 (3.32)	5.99 (3.64)	t(59) = −0.24
Binge Drinking Daysb	5.84 (8.93)	5.13 (6.44)	t(63) = −0.22	4.54 (7.95)	5.62 (7.36)	t(63) = 0.74
Total Drinks Past Monthb	75.14 (110.36)	64.83 (69.29)	t(63) = 0.37	58.74 (100.07)	71.31 (83.95)	t(63)= 1.54

Because 4 individuals were abstinent in terms of past month drinking, sample sizes for Drinks Per Drinking Day analyses were n = 23 and n = 38 for Veterans screening positive and negative for TBI, respectively, and n = 11 and n = 50 for Veterans with confirmed and nonconfirmed TBI, respectively.

^aSquare-root transformations used for t-test comparisons.

^bLog transformations used for t-test comparisons.

^*p < 0.10;

^**p < 0.05;

^***p < 0.01.

DISCUSSION

The current study extends a growing body of literature on deployment risk factors for mTBI and postdeployment health outcomes prevalent among Veterans with a history of mTBI. In this sample of heavy drinking OEF/OIF Veterans, rates of positive mTBI screens were twice as high as rates reported in other samples of OEF/OIF Veterans seeking VA health care,¹⁸ whereas rates of confirmed mTBI diagnoses were consistent with more general estimates of mTBI prevalence in this Veteran cohort.^2,3 The most common mTBI-related events reported during deployment were exposure to blasts and explosions and vehicular accidents and crashes, although the use of screening data precludes our ability to determine whether or not these events occurred separately or simultaneously (i.e., the Veteran was exposed to an IED blast while in a moving vehicle), restricting our ability to explore the cumulative effects of multiple mTBI-related events.

The current study clearly suggests, however, that Veterans screening positive for mTBI and ultimately receiving confirmed mTBI diagnoses are exposed to a myriad of combat experiences at rates exceeding those of Veterans who did not screen positive for mTBI, including events expected to be causally related to mTBI like encountering mines or booby traps. The two DRRI items assessing proximity to exploding artillery shells and missiles, events presumably associated with mTBI, discriminated between Veterans with a history of mTBI (i.e., positive mTBI screens or confirmed mTBI) and those without a history of mTBI in the expected direction, given that 80% of Veterans with positive mTBI screens and approximately 85% of Veterans with confirmed mTBIs reported being within 1 km of an exploding artillery shell. These trends were only significant when comparing Veterans with positive and negative mTBI screens, however, and it is important to note that the DRRI was constructed based on the experiences of Gulf War I Veterans.²⁴ Consequently, the wording on these two items may not accurately capture the kinds of blast experiences frequently encountered by OEF/OIF troops.

One possible explanation for the higher rates of various combat experiences reported by Veterans with positive mTBI screens and confirmed mTBI diagnoses is that, because these Veterans experienced more combat situations, they may have been at increased risk for mTBI-related experiences like blast exposure. These multiple risk exposures may at least partly explain the high rates of comorbidity between mTBI and PTSD. The observed relations between combat experiences, PTSD, and mTBI status also suggest the possibility that individuals may endorse mTBI “symptoms” which are not, in fact, because of a neurological injury, but which are instead attributable to psychological phenomena like PTSD. In other words, the domain of observable variables utilized by these indices of mTBI may have considerable overlap with other constructs including PTSD. For example, Iverson²⁰ comments on these conceptual issues by noting that individuals may endorse having experienced a vehicular accident on the screener without having experienced a physical or psychological injury at the time of the accident. Iverson²⁰ further notes that many of the immediate symptoms of brain injury assessed by the screener (i.e., symptoms in the immediate aftermath of the event) are also quite common in psychologically traumatized individuals.

In the current sample, the rate of PTSD among Veterans with positive mTBI screens was much higher than those reported in other samples of OIF Veterans,¹⁹ and this rate was similar among Veterans with confirmed mTBI diagnoses. Although the rate of PTSD among Veterans with a history of mTBI was much higher in this sample than rates reported in prior studies, it is important to note that the rate of PTSD was also higher among individuals without a history of mTBI compared to general estimates of PTSD prevalence in this Veteran population.³ The higher rate of PTSD in this sample may be explained by several factors. First, our sample consists of Veterans who were seeking medical care, and rates of PTSD are typically higher among Veterans seeking VA health care²⁹ compared to more general samples. An additional factor likely contributing to these higher rates of PTSD is that our sample consists entirely of heavy drinking Veterans, and rates of PTSD tend to be higher among Veterans with substance misuse.³⁰

Moreover, PTSD severity was a significant predictor of screening positive for mTBI but not for ultimately receiving an mTBI diagnosis. These findings are somewhat consistent with previous research suggesting that emotional factors like anxiety can affect neuropsychological functioning.³¹ So, individuals with more severe PTSD symptoms may be more likely to report cognitive or physiological problems on screeners for mTBI, whereas these problems may not necessarily be found to be directly related to mTBIs during more thorough clinical evaluations. From a psychometric standpoint, these findings suggest that the VA TBI Clinical Reminder may lack specificity. However, as with any screening instrument, sensitivity may be more important than specificity for the purpose of identifying Veterans needing further clinical evaluation.²⁰ Nevertheless, the use of such instruments for research may yield highly variable estimates of mTBI given the lack of specificity of events and symptoms used to identify mTBI.

In terms of drinking outcomes, Veterans in this sample evidenced riskier drinking patterns than those reported in the broader military population, although this observation is expected given that all Veterans in this study screened positive for heavy drinking on the AUDIT or AUDIT-C. In a population-based sample of previously deployed OEF and OIF Veterans, Ramchand et al³² reported that deployed Veterans consumed alcohol, on average, approximately 7 days per month, consumed an average of 2 drinks per drinking occasion, and reported binge drinking an average of 2 times over the course of a month. In comparison, Veterans in our sample tended to consume over twice the number of drinks per drinking day and report over twice the number of monthly binge drinking episodes as Veterans in this broader sample. However, this pattern of drinking did not seem to vary as a function of mTBI status.

Veterans with positive mTBI screens and confirmed mTBI diagnoses did not differ from Veterans without a history of mTBI on any index of alcohol use, including drinking-related consequences, quantity or frequency of past month use, or number of binge drinking days. These findings stand in contrast to other recent studies¹⁹ in suggesting that, among heavy drinking Veterans, a history of mTBI is not uniquely associated with different patterns of alcohol use. The fact that our sample was composed entirely of heavy drinking Veterans, though, restricts the range of variability in drinking outcomes, which may have limited our ability to detect differences between the mTBI groups. Nevertheless, these findings do suggest that heavy drinking Veterans screen positive for mTBI at a higher rate than indicated by prevalence estimates derived from general population-based samples of OEF/OIF Veterans (15%–19%).^2,3 Higher rates of screening positive for mTBI in this sample may reflect increased sensitivity to cognitive and somatic problems associated with alcohol use among heavy drinkers. This finding underscores the importance of screening Veterans who report hazardous drinking for other conditions like PTSD and mTBI.

The current study has several limitations coupled with several notable strengths. In terms of limitations, the current study is cross-sectional and retrospective recall of war-zone experiences and drinking may have been influenced by more severe PTSD and neurobehavioral symptoms. Many Veterans with a history of PTSD and mTBI also suffer from chronic pain and other health conditions that were not assessed in the current study but may have influenced the present findings. Furthermore, the small sample size may have limited the ability to detect actual group differences in deployment and postdeployment outcomes. Notable strengths include the use of clinical interviews for measures of PTSD and alcohol use as well as the comprehensive clinical evaluation of TBI. Future studies should attempt to explore associations between mTBI and psychosocial outcomes using more widely representative samples of Veterans.