Post-traumatic stress disorder and depression co-occurrence: Structural relations among disorder constructs and trait and symptom dimensions.

Objectives: Post-traumatic stress disorder (PTSD) and major depressive disorder (MDD) in response to trauma co-occur at high rates. A better understanding of the nature of this co-occurrence is critical to developing an accurate conceptualization of the disorders. This study examined structural relations among the PTSD and MDD constructs and trait and symptom dimensions within the framework of the integrative hierarchical model of anxiety and depression.

Design: Study participants completed clinician-rated and self-report measures during a pre-treatment assessment.

Methods: The sample consisted of 200 treatment-seeking individuals with a primary DSM-IV PTSD diagnosis. Structural equation modelling was used to examine the relationship between the constructs.

Results: The trait negative affect/neuroticism construct had a direct effect on both PTSD and MDD. The trait positive affect/extraversion construct had a unique, negative direct effect on MDD, and PTSD had a unique, direct effect on the physical concerns symptoms construct. An alternative model with the PTSD and MDD constructs combined into an overall general traumatic stress construct produced a decrement in model fit.

Conclusions: These findings provide a clearer understanding of the relationship between co-occurring PTSD and MDD as disorders with shared trait negative affect/neuroticism contributing to the overlap between them and unique trait positive affect/extraversion and physical concerns differentiating them. Therefore, PTSD and MDD in response to trauma may be best represented as two distinct, yet strongly related constructs.

Practitioner Points: In assessing individuals who have been exposed to trauma, practitioners should recognize that co-occurring PTSD and MDD appears to be best represented as two distinct, yet strongly related constructs. Negative affect may be the shared vulnerability directly influencing both PTSD and MDD; however, in the presence of both PTSD and MDD, low positive affect appears to be more specifically related to MDD and fear of physical sensations to PTSD, which is information that could be used by practitioners in the determination of treatment approach. Overall, these findings are clinically relevant in that they may inform assessment, treatment planning, and ultimately diagnostic classification.