UNDERSTANDING PTSD AND MAJOR DEPRESSIVE DISORDER CO-OCCURRENCE: STRUCTURAL RELATIONS AMONG DISORDER CONSTRUCTS AND TRAIT AND SYMPTOM DIMENSIONS by LOREN M. POST Submitted in partial fulfillment of the requirements for the degree of Master of Arts Thesis Advisor: Dr. Norah C. Feeny Department of Psychology CASE WESTERN RESERVE UNIVERSITY January, 2010 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of _____________________________________________________ candidate for the ______________________degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. 1 Table of Contents Abstract............................................................................................................................... 4 Introduction......................................................................................................................... 5 Method .............................................................................................................................. 18 Results............................................................................................................................... 24 Discussion......................................................................................................................... 27 References......................................................................................................................... 44 2 List of Tables Table 1: Mean, Standard Deviation, and Range on Model Measures .............................. 37 Table 2: Zero Order Correlations Among Measured Variables........................................ 38 Table 3: Completely Standardized Factor Loadings of Model Indicators........................ 39 Table 4: Unstandardized and Standardized Structural Regression Coefficients for Final Model....................................................................................................................... 40 3 List of Figures Figure Captions................................................................................................................. 41 Figure 1: Hypothesized Model: Relations Among PTSD and Major Depressive Disorder Constructs and Trait and Symptom Dimensions ............................................... 42 Figure 2: Final Model: Relations Among PTSD and Major Depressive Disorder Constructs and Trait and Symptom Dimensions with Standardized Coefficients............ 43 4 Understanding PTSD and Major Depressive Disorder Co-occurrence: Structural Relations Among Disorder Constructs and Trait and Symptom Dimensions Abstract by LOREN M. POST PTSD and major depressive disorder co-occur at high rates. This co-occurrence has been associated with greater disorder severity and functional impairment. In order to better understand the nature of this co-occurrence, this study examined the structural relations among the disorders and trait and symptom dimensions within the framework of the integrative hierarchical model of anxiety and depression. Results suggest that PTSD and major depressive disorder are best conceptualized as two distinct, yet strongly related constructs. The trait negative affect/neuroticism construct had a direct effect on both PTSD and major depressive disorder, partly explaining the overlap between the disorders. The trait positive affect/extraversion construct had a unique, negative direct effect on major depressive disorder and PTSD had a unique, direct effect on the physical concerns symptom construct. A clearer understanding of the trait vulnerabilities and symptoms involved in co-occurrence may help to inform both diagnostic classification and treatment. 5 Introduction Posttraumatic stress disorder (PTSD) is classified as an anxiety disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR; American Psychiatric Association, 2000). As with most of the anxiety disorders, PTSD has high rates of lifetime association and co-occurrence (defined as “the simultaneous presence in an individual of two diagnoses, which are not necessarily correlated to an appreciable extent within the population;” Lilienfeld, Waldman, & Israel, 1994, p. 78) with major depressive disorder (e.g., Breslau, Davis, Andreski, & Peterson, 1991). In the National Comorbidity Survey (Kessler, Sonnega, Bromet, Hughes, & Nelson, 1995) for example, across all disorders, major depressive disorder showed the highest rate of lifetime association with PTSD among women (48.5%) and the second highest rate among men (47.9%). High rates of co-occurring PTSD and major depressive disorder have also been found across different trauma exposed populations, such as combat veterans (95% lifetime and 50% co-occurring; Bleich, Koslowsky, Dolev, & Lerer, 1997), motor-vehicle accident survivors (53% co-occurring; Blanchard, Buckley, Hickling, & Taylor, 1998), and physical assault survivors (49% co-occurring; Nixon, Resick, & Nishith, 2004). Moreover, there appears to be a synergistic aspect to the co-occurrence of PTSD and major depressive disorder, as individuals with co-occurring PTSD and major depressive disorder tend to display more severe symptoms of both disorders and worse functional impairment than individuals with either PTSD or major depressive disorder alone (Blanchard et al., 1998; Momartin, Silove, Manicavasagar, & Steel, 2004; Nixon et al., 2004; Shalev et al., 1998). Further, this co-occurrence is associated with a number of negative correlates and outcomes including increased risk for attempted suicide 6 (Oquendo et al., 2005), a more chronic course of impairment and psychopathology (Breslau et al., 1991), and attenuated treatment response (Green et al., 2006). Thus, a closer examination of PTSD and major depressive disorder co-occurrence is warranted in order to better understand the shared and unique vulnerability and symptom dimensions driving the high rates of co-occurrence and related disorder severity. To date, examining the nature of the co-occurrence of PTSD and major depressive disorder has been approached in several ways. There has been exploration of the overlapping PTSD and major depressive disorder diagnostic criteria (i.e., insomnia, impaired concentration, and anhedonia) possibly contributing to the high rates of diagnostic co-occurrence. For instance, among a sample of combat veterans, Bleich et al. (1997) demonstrated that when shared symptoms were eliminated from the diagnostic criteria, there were relatively small changes in the diagnostic frequency for each disorder. Indeed, of those originally diagnosed with lifetime and current major depressive disorder, 98% and 93% were still diagnosed as such, respectively, after overlapping symptom removal. The rates of maintaining the PTSD diagnosis were lower, with 70% still diagnosed as having lifetime PTSD and 55% still diagnosed as having current PTSD. Such findings suggest that PTSD may be more often accounted for by major depressive disorder than major depressive disorder is by PTSD. Overall, however, symptom overlap appears to have only a moderate effect on rates of PTSD, as over half of the participants maintained their lifetime and current diagnosis. Therefore, these results suggest that PTSD may be a distinct diagnosis co-occurring with major depressive disorder, despite symptom overlap. In further examining symptom overlap, Blanchard and colleagues (1998) investigated the possibility that co-occurrence may be due to the fact that after 7 accounting for the three symptoms shared with PTSD only two of the remaining six major depressive disorder symptom criteria are needed for the diagnosis of major depressive disorder. Therefore, in diagnosing co-occurring major depressive disorder among individuals with PTSD, it was suggested that four to five additional major depressive disorder symptom criteria, as opposed to just two, be met. However, Blanchard et al. (1998) found that individuals with PTSD who endorsed more major depressive disorder symptoms (i.e., 7-9) compared to those who endorsed fewer major depressive disorder symptoms (i.e., 5-6) displayed similar levels of subjective distress and impairment. Because co-occurrence has been associated with disorder severity (e.g., Kessler, Chiu, Demler, & Walters, 2005), these results suggest that symptom overlap is an insufficient explanation for PTSD and major depressive disorder co-occurrence. Beyond the explanation that observed high rates of co-occurring PTSD and major depressive disorder are due to overlapping symptoms, others have investigated whether PTSD and major depressive disorder represent two distinct constructs, or whether their co-occurrence represents a single general traumatic stress construct. For instance, Blanchard and colleagues (1998) conducted factor analyses using measures of PTSD and major depressive disorder symptomatology to evaluate and compare how a single-factor model of posttraumatic stress symptoms (i.e., unitary response to trauma) and a two- factor model of posttraumatic stress symptoms (i.e., PTSD and major depressive disorder) fit the data for their traumatized population. The model fit indices were improved by the two-factor