Posttraumatic stress disorder and depressive symptoms: joined or independent sequelae of trauma?

The nature of co-morbidity between posttraumatic stress disorder (PTSD) and depression has been the subject of much controversy. This study addresses this issue by investigating associations between probable PTSD and depressive symptoms in a prospective, longitudinal sample of combat veterans.

Symptoms of PTSD and depression were assessed at 3 points of time (i.e., 1991, 2003, 2008) over a period of 17 years utilizing the PTSD Inventory and the SCL-90 (Derogatis, 1977). Two groups of combat veterans, 275 former prisoners of war (ex-POWs) and 219 matched combatants (controls), were assessed. Data were analyzed using descriptive statistics, latent variable modeling, and confirmatory factor analysis.

A series of χ(2) tests revealed that the prevalence proportions of depressive symptoms and probable PTSD were higher among ex-POWs compared to controls at all time points. The prevalence of depressive symptoms was higher than the prevalence of PTSD symptoms in both groups at the each of the times. Latent Trajectories Modeling (LTM) indicated that while ex-POWs' PTSD symptom severity increased over time, the severity of symptoms remained stable among controls. Parallel Process Latent Growth Modeling (PLGM) revealed a positive bi-directional relationship whereby PTSD symptoms mediated the affect of captivity on depressive symptoms and depressive symptoms mediated the affect of captivity on PTSD symptoms over time. Utilizing Confirmatory Factor Analysis (CFA), a single factor model emerged for depressive and PTSD symptoms.

The findings suggest that while depression and PTSD seem to be different long-term manifestations of traumatic stress, accounted for in part by the severity of the trauma, they both may be parts of a common general traumatic stress construct. Clinical and theoretical implications of these findings are discussed.