Mild traumatic brain injury, PTSD symptom severity, and behavioral dyscontrol: a LIMBIC-CENC study

Background Behavioral dyscontrol occurs commonly in the general population and in United States service members and Veterans (SM/V). This condition merits special attention in SM/V, particularly in the aftermath of deployments. Military deployments frequently give rise to posttraumatic stress disorder (PTSD) and deployment-related mild TBI traumatic brain injury (TBI), potentially leading to manifestations of behavioral dyscontrol. Objective Examine associations among PTSD symptom severity, deployment-related mild traumatic brain injury, and behavioral dyscontrol among SM/V. Design Secondary cross-sectional data analysis from the Long-Term Impact of Military-Relevant Brain Injury Consortium – Chronic Effects of Neurotrauma Consortium prospective longitudinal study among SM/V (N = 1,808). Methods Univariable and multivariable linear regression models assessed the association and interaction effects between PTSD symptom severity, as assessed by the PTSD Checklist for the Diagnostic and Statistical Manual, 5th edition (PCL-5), and deployment-related mild TBI on behavioral dyscontrol, adjusting for demographics, pain, social support, resilience, and general self-efficacy. Results Among the 1,808 individuals in our sample, PTSD symptom severity (B = 0.23, 95% CI: 0.22, 0.25, p < 0.001) and deployment-related mild TBI (B = 3.27, 95% CI: 2.63, 3.90, p < 0.001) were significantly associated with behavioral dyscontrol in univariable analysis. Interaction effects were significant between PTSD symptom severity and deployment mild TBI (B = −0.03, 95% CI: −0.06, −0.01, p = 0.029) in multivariable analysis, indicating that the effect of mild TBI on behavioral dyscontrol is no longer significant among those with a PCL-5 score > 22.96. Conclusion Results indicated an association between PTSD symptom severity, deployment-related mild TBI, and behavioral dyscontrol among SM/V. Notably, the effect of deployment-related mild TBI was pronounced for individuals with lower PTSD symptom severity. Higher social support scores were associated with lower dyscontrol, emphasizing the potential for social support to be a protective factor. General self-efficacy was also associated with reduced behavioral dyscontrol.


Introduction
Behavioral dyscontrol is a challenging clinical problem that cuts across traditional diagnostic boundaries.Wotzel and Arciniegas provide an overview of the literature that encompasses a range of terms describing behavioral dyscontrol following injury, which include emotional lability, irritability, anger, aggression, and challenges in selfregulation (1).These various symptoms denoting behavioral dyscontrol present clinically challenging sequelae that frequently impede rehabilitation efforts, disrupt social support networks and compromise optimal recovery (1,2).The absence of a standardized or universally accepted definition and the limitations in delineating mental and behavioral presentations following TBI contribute to the complexity of behavioral dyscontrol (1).Although a multitude of factors can influence the development and severity of behavioral dyscontrol, posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) have been identified as important contributors (2, 3).Veterans who have served in combat deployments are at risk of experiencing TBI and developing PTSD, which also increases their risk for behavioral dyscontrol (4).Understanding potential links among PTSD, deployment mild TBI, and behavioral dyscontrol can inform postdeployment healthcare delivery for Service members and Veterans (SM/Vs).
Deployment-related mild TBI can disrupt neural pathways crucial for impulse control (2).Due to heterogeneity in injury, mild TBI may manifest in various behavioral dyscontrol symptoms, including explosive outbursts, verbal and physical aggression, impaired judgment and planning abilities, and limited self-awareness (1,2,5).Similarly, some Veterans with PTSD report experiencing challenges with self-regulation, which may also be associated with symptoms of behavioral dyscontrol such as agitation and explosive behavior (1,2,5).
The present analysis aimed to investigate the associations between history of deployment-related mild TBI, PTSD symptoms, and behavioral dyscontrol in a cohort of combat SM/Vs.Given that prior work identified poorer outcomes for SM/Vs with TBI and high PTSD symptom severity, we hypothesized that behavioral dyscontrol would be highest among those with deployment-related mild TBI and high PTSD symptom severity (6)(7)(8).

Design
This cross-sectional study utilized data from the baseline visit of the longitudinal, multi-center Prospective Longitudinal Study (PLS) conducted by the Long-term Impact of Military-relevant Brain Injury Consortium-Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC) (9).The primary objective of the PLS is to assess the effects of mild TBI (s) and other comorbidities on neurological and psychological outcomes among combat-exposed SM/Vs (10).During the baseline visit, participants completed a comprehensive assessment, which included structured interviews, questionnaires, neuropsychological testing, and biometric measurements (11).

Participants
The PLS is conducted across 11 recruitment sites.Enrollment is ongoing, with over 2,000 SM/Vs enrolled.Participants were recruited primarily through targeted mailings.Eligible individuals included SM/Vs who had deployed to a combat zone, were at least 18 years of age, and had no history of moderate to severe TBI or major neurological or psychiatric illnesses resulting in a significant longterm decrease in functional status (e.g., schizophrenia, spinal cord injury) (9).Common comorbidities, including PTSD and depression, were permitted.The study obtained approval from the regional Institutional Review Boards of the participating facilities, and written consent was obtained from all participants before any procedures were conducted.The available sample size for the presented analyses at the time of database extraction was N = 2,069.Participants were excluded from these analyses for missing data on key measures (n = 118) and for noncredible symptom-reporting profiles on the mild Brain Injury Atypical Symptoms (mBIAS) questionnaire (10) (n = 143).These exclusions left a final analytic sample size of N = 1,808.Within this cohort, 278 experienced TBI during deployment only, 680 TBI from both deployment and non-deployment settings, 507 had TBI solely in non-deployment settings, and 343 individuals had no history of TBI.

Measures
The primary outcome, behavioral dyscontrol, was assessed by selfreport using the 10-item Traumatic Brain Injury Quality of Life (TBIQOL) questionnaire, which measures emotional and behavioral dyscontrol, including disinhibition, emotional lability, irritability, impatience, and impulsiveness (11,12)-the primary characteristics of behavioral dyscontrol.The total score ranges from 10 to 50, with higher scores indicating higher levels of dyscontrol (12).

Independent variables
History of deployment-related mild TBI was evaluated using the Virginia Commonwealth University Retrospective Concussion Diagnostic Interview (VCU-rCDI)-a structured interview developed for the PLS to facilitate the classification of all potential concussive events (PCEs) experienced throughout an individual's lifetime (13).PCEs are first identified via a modified OSU TBI ID interview version (13).Each PCE is evaluated with the VCU-rCDI to determine if it meets the criteria for mild TBI and to gather information on setting, mechanism, and other clinical characteristics (13).Diagnostic determinations were consistent with the VA/ Department of Defense (DoD) standard definition of mild TBI and the American Congress of Rehabilitation Medicine guidelines (14,15).Variables utilized for this analysis included deployment and non-deployment designation for each mild TBI based on whether the TBI occurred during a combat deployment or some other time during life.
PTSD symptom severity was assessed using the PTSD Checklist for the Diagnostic and Statistical Manual, 5th edition (PCL-5) (16).This 20-item self-report measure utilizes a 5-point Likert scale to evaluate how bothered an individual has been by symptoms associated with PTSD in the past 30 days.Total scores range from 0 to 80, with greater scores indicating greater symptom severity (16).Participants scoring 33 or higher on the PCL-5 were classified as positive for probable PTSD (16).

Covariates
Previous studies have identified key symptoms associated with PTSD, mild TBI, and behavioral dyscontrol (17,18) that were chosen as covariates for the present analysis.
The Euroqol 5 measures pain/discomfort on a 5-point ordinal scale, allowing respondents to assess their current pain as none, slight, moderate, severe, or extreme (19).Meanwhile, the TBI Qol Pain Interference Short-Form comprises a 10-item questionnaire prompting participants to rate the extent of pain interference across functions like family life, daily tasks, mental health, and overall quality of life.Responses are noted on a 5-point ordinal scale (1-5), and total scores range from 10 to 50 points, with higher scores reflecting greater interference (19).
General Self-Efficacy (GSE) was measured using a 10-item selfreported questionnaire that measures an individual's perceived ability to solve problems and achieve their goals (20).Response options range from 1 (Not at all true) to 5 (Exactly true), with a total score range of 10-50 (20).
The Deployment Risk and Resilience Inventory-2 (DRRI-2) Social Support subscale is a comprehensive self-report assessment tool designed to evaluate the degree of social support available to individuals, particularly those who have experienced military deployment and related challenges (21).It encompasses a range of factors that contribute to an individual's perception of social support, including emotional, instrumental, and informational assistance from family members, friends, and peers (21).The subscale aims to quantify the extent to which individuals perceive themselves as having access to a robust support network during and after deployment.Respondents are asked to rate their level of agreement or frequency on a Likert-type scale from 1 to 5, where higher scores indicate higher levels of perceived social support (21).
Lifetime Mild TBI history is assessed in LIMBIC-CENC PLS using a validated process, cataloging each participant's potential concussive events through a modified Ohio State University TBI Identification (OSU TBI-ID) (12).A retrospective Concussion Diagnostic Interview generates a preliminary algorithm based TBI diagnosis, which undergoes rigorous review against medical records by a centralized expert committee.Final determinations align with the VA/DoD common definition of mild TBI.
Blast mechanisms are classified as blast-related or not, and if blastrelated, as pure blast or mixed blast-blunt.Subclassifications for analysis include 1-2 mild TBIs vs. 3+ (repetitive mild TBI), mild TBIs with or without PTA, blast-related or not, and pure blast vs. non-blast/ mixed blast-blunt mild TBIs (12).
We also included sociodemographic factors (age, sex, education, and race/ethnicity) selected based on the existing literature to adjust for their potential impact in multivariable analysis.

Statistical methods
Demographic and clinical outcomes are reported using means and standard deviation (SD), medians and interquartile ranges (IQR), ranges for continuous variables, and counts and percentages for categorical variables.To compare these variables between deploymentrelated mild TBI exposure (yes/no) group, we used non-parametric Wilcoxon rank sum tests for continuous variables and chi-square or Fisher's exact tests for categorical variables, as appropriate.There were no independent or interaction effects of non-deployment-related mild TBI on behavioral dyscontrol; therefore, non-deployment TBI was excluded from the analysis.Univariable and multivariable linear regression models assessed independent and interactive associations between variables of interest and behavioral dyscontrol.The multivariable model included the interaction term and adjusted for age, sex, ethnicity, race, Euroqol 5 -pain dimension scores, DRRI-2 Social Support scores, and GSE scores.Multicollinearity was considered tolerable if the generalized variance inflation factor (GVIF) was <2.24 (22).Johnson-Neyman analysis probed significant interaction effects.We report Betas (B) with 95% confidence intervals (CI) for each

Results
In our analytic sample of 1,808 individuals, 53% (n = 958) had deployment-related mild TBI, and 47% (n = 850) had no history of deployment mild TBI.Studying both deployment-and non-deployment-related mild TBI is fundamental for a comprehensive understanding of the diverse causes, mechanisms, and long-term impacts of TBI and the individuals affected by these injuries (24,25).Table 1 presents the demographic characteristics of the sample, stratified by deployment-related mild TBI status.Most participants were male (87.0%) and White (73.0%), with a median age of 39 years (IQR: 33, 48).There were significant differences in behavioral dyscontrol scores between SM/Vs with (M = 23.6,SD = 6.8) versus without (M = 20.4,SD = 6.9) history of deployment-related mild TBI.Social support scores were higher among SM/Vs without (M = 40.1,SD = 7.9) compared to those with a history of deploymentrelated mild TBI (M = 38.1,SD = 8.1).Finally, SM/Vs without a history of deployment-related mild TBI reported greater self-efficacy (M = 32.7,SD = 4.7) than SM/Vs with a history of deployment-related mild TBI (M = 31.4,SD = 4.8).
Among SM/Vs who experienced both blast and non-blast deployment-related mild TBI, but no PTSD, dyscontrol scores were found to be 1.04 points higher compared to those with blast-only deployment-related mild TBI (B = 1.04, 95% CI: 0.09, 1.98, p = 0.005).
Figure 2 interaction effect between deployment-related mild TBI status and PTSD symptom severity scores on behavioral dyscontrol.The slope of PTSD severity scores is steeper in SM/Vs without deployment-related mild TBI than those with no deployment-related mild TBI have lower observed behavioral dyscontrol total scores.

Discussion
We hypothesized that SM/Vs with greater PTSD symptom severity and deployment-related mild TBI would report increased behavioral dyscontrol.Our results partially supported this hypothesis, demonstrating that PTSD symptom severity and deployment-related mild TBI were associated with behavioral dyscontrol in univariable and multivariable models adjusting for race, ethnicity, and sex.Further, results indicated a significant interaction effect between deploymentrelated mild TBI and PTSD symptoms, in which the effect of deployment-related mild TBI was significant only among those with lower severity of PTSD symptoms (PCL-5 scores of 0-23).This finding suggests a clear effect of deployment-related mild TBI when PTSD symptoms are lower, but that when PTSD symptoms are more severe, PTSD symptoms likely account for effects on behavioral dyscontrol.Moreover, those with high social support and self-efficacy scores also reported significantly lower scores on behavioral dyscontrol.
The observed elevation in dyscontrol scores among SM/Vs with both blast and non-blast deployment-related mild TBI, as opposed to those with blast-only TBI, provides a noteworthy point of discussion in the broader context of TBI research.The documented difference in dyscontrol scores, even after adjusting for other relevant factors, underscores the complexity of deployment-related mild TBI-related outcomes and the importance of considering injury mechanisms.The distinct neurological effects associated with blast and non-blast injuries may contribute uniquely to dyscontrol, reflecting the complex interplay between injury characteristics and resulting behavioral sequelae.Moreover, the absence of PTSD symptoms in the studied population emphasizes the specific impact of TBI subtypes on dyscontrol, independent of comorbid psychological conditions.
The association between elevated social support scores and diminished behavioral dyscontrol scores among SM/Vs emphasizes the potential importance of social support as a protective factor.Existing research demonstrates that social support from the military unit, friends, and family buffer the relationship between stressor exposure and posttraumatic stress symptoms.Social support from familial, peer, or community relationships is a stabilizing force that helps SM/V navigate the complexities of life after military service (26).Support networks can offer emotional reassurance, facilitate coping strategies, and provide a sense of belonging and understanding (26).Wilks and colleagues analyzed 2,467 Iraq/Afghanistan-era Veterans and found that TBI was associated with suicidal ideation, and social support was negatively associated with suicide ideation.Conversely, limited social support has been linked to heightened levels of stress, increased symptom severity, and a more challenging rehabilitation journey (27, 28).These findings, coupled with the findings in our study, help explain the connections between PTSD symptom severity and behavioral dyscontrol symptoms, and may bolster the need for additional social and family support as treatment adjuncts to lower the risk of these adverse outcomes.
Similarly, our results suggest that greater self-efficacy may also be protective and lead to decreased behavioral dyscontrol.The ability to effectively navigate challenges impacts cognitive, behavioral, affective, and functional outcomes and demonstrates a significant protective influence (29,30).Research consistently demonstrates that high levels of self-efficacy increase resiliency among SM/Vs and are closely associated with better mental health outcomes (29,30).Selfefficacy may also be an important factor in treatment.In one study of     Increasing patients' level of self-efficacy may be important for successful treatment of psychological distress in SM/Vs (30).Greater self-efficacy is associated with better mental health outcomes, such as enhanced coping skills, increased resilience, and reduced levels of anxiety and depression (29).The perception of being capable of resolving problems and attaining personal goals may empower SM/Vs to exert greater control over their actions and reactions, subsequently mitigating symptoms of behavioral dyscontrol (31).

Study strengths
The present analysis has several inherent strengths.The sample size was substantial, representing 1,808 well-characterized SM/Vs with combat exposure from the LIMBIC-CENC multi-center cohort.This ensured robustness as we rigorously evaluated their lifetime mild TBI histories and benefited from the extensive data collected in the comprehensive assessments.The study controlled for symptom validity by excluding participants with non-credible symptom profiles on a validated measure.

Study limitations
While our study sheds light on the effects of PTSD and deployment-related mild TBI on behavioral dyscontrol, it is essential to acknowledge several limitations.A significant limitation is that many of the study measures were self-reported and therefore cannot provide definitive clinical diagnoses.Additionally, inherent to the cross-sectional design, causal inferences and temporal dynamics remain constrained.Notably, the study lacks a systematic assessment of structural brain abnormalities, medications, and psychological evaluations at baseline which may have explained variance in our results.

Implications for future research
Further research is warranted to identify how self-efficacy and social support influence behavioral dyscontrol in SM/Vs with PTSD and/or deployment-related mild TBI.Longitudinal studies can contribute to understanding the temporal relationship between self-efficacy and behavioral dyscontrol symptoms, elucidating whether changes in self-efficacy precede or follow improvements in behavioral regulation.Investigating the influence of social Examining the types of support (e.g., emotional, instrumental, informational) and the sources of support (e.g., family, friends, healthcare providers) can provide a comprehensive understanding of how different aspects of social support impact behavioral regulation (32).A thorough exploration is critical to understanding the complex relationship of deployment-related mild TBI, PTSD symptom severity, and related psychosocial constructs in shaping behavioral dyscontrol among SM/Vs.Future research using longitudinal designs should provide a more comprehensive understanding of the temporal dynamics between deployment-related mild TBI, PTSD, and dyscontrol, which may influence the observed associations between these conditions.

Conclusion
PTSD and mild TBI are commonly diagnosed during or following military deployments, and both are associated with behavioral dyscontrol in SM/Vs.The present analysis demonstrated that PTSD symptom severity and deployment-related mild TBI were each associated with behavioral dyscontrol in univariable and multivariable models adjusting for race, ethnicity, and sex.Deployment-related mild TBI primarily contributes to behavioral dyscontrol in the absence of prominent PTSD symptom severity.The findings highlight the complex relationship between PTSD symptoms and mild TBI resulting from deployment, particularly with regard to behavioral dyscontrol.Consequently, there is a pressing need for a comprehensive understanding and targeted interventions within clinical, research, and policy spheres, given the interdependence of these conditions.

TABLE 1
Summary of demographic variables stratified by deployment-related mild TBI.

TABLE 2
Behavioral dyscontrol score by deployment-related mild and PTSD.The number of mild TBI is the same as number of lifetime TBI if none of the TBIs are moderate-severe. a