Examining the latent structure mechanisms for comorbid posttraumatic stress disorder and major depressive disorder

Background: Posttraumatic stress disorder (PTSD) is a complex psychiatric illness that can be difficult to diagnose, due in part to its comorbidity with major depressive disorder (MDD). Given that researchers have found no difference in prevalence rates of PTSD and MDD after accounting for overlapping symptoms, the latent structures of PTSD and MDD may account for the high comorbidity. In particular, the PTSD Negative Alterations in Cognition and Mood (NACM) and Hyperarousal factors have been characterized as non-specific to PTSD. Therefore, we compared the factor structures of the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) PTSD and MDD and examined the mediating role of the PTSD NACM and Hyperarousal factors on the relationship between MDD and PTSD symptom severity. Methods: Participants included 598 trauma-exposed veterans (M-age = 48.39, 89% male) who completed symptom self-report measures of DSM-5 PTSD and MDD. Results: Confirmatory factor analyses indicated an adequate-fitting four-factor DSM-5 PTSD model and two-factor MDD model. Compared to other PTSD factors, the PTSD NACM factor had the strongest relationship with the MDD Affective factor, and the PTSD NACM and Hyperarousal factors had the strongest association with the MDD Somatic factor. Further, the PTSD NACM factor explained the relationship between MDD factors and PTSD symptom severity. More Affective and Somatic depression was related to more NACM symptoms, which in turn were related to increased severity of PTSD. Limitations: Limitations include the reliance on self-report measures and the use of a treatment-seeking, trauma-exposed veteran sample which may not generalize to other populations. Conclusions: Implications concerning the shared somatic complaints and psychological distress in the comorbidity of PTSD and MDD are discussed.