Dimensional structure of DSM-5 posttraumatic stress symptoms: Support for a hybrid Anhedonia and Externalizing Behaviors model
Introduction
There has been longstanding debate within the academic literature with regard to the underlying dimensionality of Posttraumatic Stress Disorder (PTSD) (cf. Yufik and Simms, 2010). The most recent, 5th edition of the DSM (DSM-5; American Psychiatric Association, 2014), characterizes PTSD as a heterogenous disorder comprised of four symptom clusters which supersedes the tripartite model utilized by the DSM from 1980 to 2013. A body of confirmatory factor analytic (CFA) studies found that the dimensional structure of DSM-based PTSD symptoms, as represented in the DSM-IV (APA, 1994) through to the DSM-IV-TR (APA, 2000), are best represented by four rather than three symptom clusters (King et al., 1998, Simms et al., 2002). Indeed, two four-factor models of PTSD—the Emotional Numbing model and the Dysphoria model—have been proposed and supported across a variety of trauma-exposed populations from a variety of cultural backgrounds and utilizing different assessment instruments (Elhai and Palmieri, 2011, Gootzeit and Markon, 2011, Yufik and Simms, 2010). The recent proposal of two 6-factor DSM-5 models—the Anhedonia model and the Externalizing Behavior model (Liu et al., 2014, Tsai et al., 2014, respectively)—is reminiscent of earlier debates surrounding the two 4-factor DSM-IV/DSM-IV-TR models. The current study focuses on the assessment of these models in comparison to a 7-factor Hybrid model, which combines key features of both 6-factor models, in order to determine which model better represents the latent structure of DSM-5 PTSD symptoms. This is an important line of research, as it can help shed light on diagnosis, treatment planning, and elucidating the underlying nature of PTSD.
The debate surrounding which one of the two 4-factor DSM-IV-TR models—the Emotional Numbing model (King et al., 1998; re-experiencing, avoidance, numbing, hyperarousal) or the Dysphoria model (Simms et al., 2002; re-experiencing, avoidance, dysphoria, hyperarousal)—best represented the dimensional structure of PTSD was never fully resolved. The Emotional Numbing model was conceived from theoretical and empirical support that Numbing and Avoidance were two distinct factors (Asmundson, Stapleton, & Taylor, 2004), whereas the Dysphoria model was conceived on proposals that certain PTSD items, the dysphoric items, were less specific to the overall PTSD construct (cf. Watson, 2009). Of note, a meta-analytic review of 40 CFA studies concluded that the Dysphoria model provided modestly better fit to the pooled data compared to the Emotional Numbing model (Yufik and Simms, 2010). Given marginal differences in fit, however, it is entirely plausible that a different selection of PTSD studies could have resulted in better fit being demonstrated by the Emotional Numbing model. Ultimately, the two four-factor models differed in their assignment of three PTSD symptoms—sleep difficulties, anger/irritability, and difficulty concentrating, which may not be unique indicators of specific factors (Shevlin et al., 2009).
The most recent development in the study of the dimensional structure of DSM-IV-TR PTSD symptoms (APA, 2000) was the proposal of the Dysphoric Arousal model, which posits a 5-factor model of re-experiencing, avoidance, numbing, dysphoric arousal, and anxious arousal symptoms (Elhai et al., 2011). The key difference from preceding four-factor models was the separation of hyperarousal into two distinct clusters of dysphoric arousal and anxious arousal. This was based on Watson's (2005) proposal that items representing sleep disturbance, irritability, and difficulty concentrating involve general distress and/or dysphoria which is characteristic of depressive disorders, whereas remaining hyperarousal items of hypervigilance and exaggerated startle are conceptually different and more characteristic of fear-based disorders (Elhai et al., 2011). This model quickly gathered empirical support across a variety of samples, which differed with respect to trauma exposure, life stage (adolescence or adulthood), culture, and PTSD assessment instrument (Armour et al., 2013a, Armour et al., 2013b, Armour et al., 2012,; Contractor et al., 2013, Pietrzak et al., 2012, Reddy et al., 2013, Wang et al., 2013). The five factors that comprise the Dysphoric Arousal model have additionally been shown to differentially relate to health and neurobiological variables (Harpaz-Rotem et al., 2014, Pietrzak et al., 2013a, Pietrzak et al., 2013b).
The proposal and developing evidence base of the Dysphoric Arousal model coincided with the release of DSM-5 (APA, 2014). Given that the DSM-5 was published in May 2013, it was preceded by the wealth of empirical evidence supporting either the Emotional Numbing model or the Dysphoria model. The Dysphoric Arousal model had likely not gained sufficient momentum to be considered for DSM-5. Thus, it was no surprise that the DSM-5 criteria for PTSD included a 4-factor PTSD model. In this model, however, a number of the existing symptoms were revised and three additional symptoms were added. Therefore, the 4-factor model of PTSD in the DSM-5 is not a direct replication of the Emotional Numbing or Dysphoria model. Of note, this model most closely resembles the Emotional Numbing model. Specifically, the DSM-5 model of PTSD includes re-experiencing (RE), avoidance (AV), negative alterations in cognitions and mood (NACM; similar to the numbing model's numbing factor), and alterations in arousal and reactivity (AR; similar to the numbing model's hyperarousal factor) symptom clusters (Friedman et al., 2011).
Since the publication of the DSM-5, several researchers have investigated the fit of the DSM-5 4-factor model in data gleaned from a national sample of U.S. adults, a clinical sample of U.S. veterans, undergraduate psychology students, and primary care patients (Armour et al., 2014, Biehn et al., 2013, Contractor et al., 2014, Elhai et al., 2012, Miller et al., 2013). The general trend in these studies has been to compare the DSM-5 model to a modified DSM-5 model, which more closely represents the DSM-IV-TR Dysphoria model. To date, the DSM-5 model has received the most support; however, Miller et al. (2013) found support for a DSM-5 Dysphoria model in their national sample of U.S. adults and clinical sample of veterans. Thus, these findings mirror those of the two DSM-IV-TR 4-factor models in that neither model is conclusively preferential.
Recently, two separate research teams simultaneously published new DSM-5 PTSD models comprised of 6-factors (Liu et al., 2014, Tsai et al., 2014). Liu et al. (2014) assessed PTSD's latent structure using data from Chinese earthquake survivors (N = 1196) who were assessed for PTSD using the PTSD checklist for DSM-5 (PCL-5). In total, six competing DSM-5 models were assessed, including the DSM-5 four-factor model, a Dysphoria version of this model, a Dysphoric Arousal version of the DSM-5 model, and a newly proposed 6-factor Anhedonia model. The latter model incorporated both the separation of hyperarousal as per the Dysphoric Arousal model, as well as the separation of the new NACM factor into two distinct constructs of ‘negative alterations in cognitions and mood’ and ‘anhedonia’; representing positive and negative affect (Watson, 2005, Watson, 2009, Watson et al., 2011). The 6-factor Anhedonia model was found to better fit these data compared to all assessed alternative models.
Tsai et al. (in press), assessed PTSD's latent structure using PCL-5 data from a nationally representative sample of U.S. veterans (N = 1484). Once again, these researchers aimed to build on the Dysphoric Arousal model by incorporating dysphoric arousal and anxious arousal factors whilst further evaluating the addition of a new “externalizing behaviors” factor comprised of irritable or aggressive behavior and self-destructive or reckless behavior (a new symptom added to PTSD's Criterion E in DSM-5). The symptoms in this factor are deemed externalizing given they assess self-initiating aggressive behaviors which are thought to represent deficits in emotion regulation and impulse control (Friedman, 2013, Roberton et al., 2012). These are distinct from other symptoms located in the E criterion which measure thoughts, feelings, and passive experiences. Three competing models were tested in this study: the DSM-5 model, the DSM-5 Dysphoria model, and a newly proposed 6-factor ‘Externalizing Behaviors’ model, and assessed in the total sample, a subsample of female veterans only, and a subsample of veterans with lifetime PTSD. Results revealed that the 6-factor Externalizing Behaviors model provided a better fit to the data compared to the two alternative models across all three samples. Symptom mappings of the DSM-5 (APA, 2014), Anhedonia (Liu et al., 2014), and Externalizing Behaviors (Tsai et al., in press) models are shown in Table 1.
The two 6-factors models are similar in that both group the same items together to represent re-experiencing, avoidance, and anxious arousal symptoms. However, whereas the Externalizing model includes a NACM factor comprised of seven PTSD symptoms, the Anhedonia model proposes that this factor is comprised of only four PTSD items. The remaining three items are used to create an anhedonia factor. Similarly, the Anhedonia model suggest a dysphoric arousal factor comprised of four symptoms whereas the Externalizing Behaviors model proposes the inclusion of only two symptoms; the remaining two items comprise the externalizing behaviors factor.
In the current study, we propose a hybrid model that combines key features of both the Anhedonia and Externalizing 6-factor DSM-5 PTSD models, including RE, AV, negative affect, anhedonia, externalizing behavior, anxious arousal, and dysphoric arousal. As a result, the hybrid model is based on theoretical and empirical evidence which proposes that hyperarousal should consist of anxious and dysphoric arousal; that negative and positive affect are two distinct constructs; and that externalizing behaviors characterized by difficulties with emotion regulation and impulse control and may constitute a separate factor distinct from other PTSD symptoms representing passive experiences, thoughts, and feelings (Friedman, 2013, Steiner et al., 1997, Watson, 2005, Watson, 2009, Watson et al., 2011).
Models assessed herein were the current DSM-5 model, the DSM-5 Dysphoria model, the DSM-5 Dysphoric Arousal model, the Anhedonia model, the Externalizing Behaviors model, and a newly proposed 7-factor Hybrid model. We evaluated these models using CFAs in two diverse samples: a nationally representative U.S. veteran sample and a trauma-exposed U.S undergraduate student sample. We hypothesized that the 7-factor Hybrid model would evidence superior fit given that it combines a number of theoretically and empirically support revisions to PTSD's latent structure. This model can be viewed in Fig. 1.
Section snippets
U.S. veterans
The National Health and Resilience in Veterans Study (NHRVS) is a nationally representative survey of 1484 U.S. veterans that was conducted between September to October 2013. Participants completed a 60-min anonymous web-based survey. The NHRVS sample was drawn from a research panel of more than 80,000 households maintained by GfK Knowledge Networks, Inc., a survey research firm that owns and uses KnowledgePanel®, a probability-based, online non-volunteer access survey panel of a nationally
U.S. veterans
The Trauma History Screen (THS; Carlson et al., 2011) is a self-report measure that assesses the lifetime occurrence of 14 potentially traumatic events. These events include early life events such as physical or sexual assault during childhood; as well as events that more commonly occur in adulthood, such as motor vehicle accident and unexpected loss of a loved one. An additional potentially traumatic event, life-threatening illness or injury item, was added to the THS in the NHRVS. Potentially
Results
Based on DSM-5 diagnostic criteria in the NHRVS veteran sample, 143 (weighted = 12.0%) screened positive for lifetime PTSD and 64 (weighted = 5.2%) for past-month PTSD. In the Midwestern sample 4.02% of the undergraduate sample would meet the criteria for a probable PTSD diagnosis.
Discussion
The current study assessed six distinct DSM-5 PTSD models comprising between 4- and 7-factors of PTSD, across two diverse samples of veterans and university students. Our newly proposed 7-factor hybrid model was deemed to provide superior fit to both samples compared to all the other models. The 7-factor hybrid model was derived from theoretical and empirical evidence and consolidates previous work supporting findings that hyperarousal symptoms consist of anxious and dysphoric arousal (Elhai
Role of the funding source
The funding source had no role in study design; in the collection, analysis and interpretation of data; in the writing of the report; or in the decision to submit the paper for publication.
Contributors
CA conducted the literature review, conceptualized the study design, assisted with the analysis, wrote the first draft of the manuscript, and handled subsequent drafts after receiving co-authors feedback.
JT conducted the veteran analysis and commented on drafts.
TD conducted the student analysis and commented on drafts.
RC assisted with the student analysis and commented on drafts.
TB collected the student data and commented on drafts.
JE assisted with the analysis and commented on drafts.
RP
Conflict of interest
Dr. Pietrzak is a scientific consultant to Cogstate, Ltd. for work that bears no relationship to the present study. None of the other authors report any conflicts of interest.
Acknowledgments
The National Health and Resilience in Veterans Study was funded by the U.S. Department of Veterans Affairs National Center for Posttraumatic Stress Disorder (PTSD). Preparation of this report was supported in part by the Clinical Neurosciences Division of the National Center for PTSD and a private donation. The views and opinions expressed in this report are those of the authors and should not be construed to represent the views of sponsoring organizations, agencies, or the U.S. government.
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