Posttraumatic stress disorder and depression following trauma: understanding comorbidity

OBJECTIVE: Posttraumatic stress disorder (PTSD) and major depression occur frequently following traumatic exposure, both as separate disorders and concurrently. This raises the question of whether PTSD and depression are separate disorders in the aftermath of trauma or part of a single general traumatic stress construct. This study aimed to explore the relationships among PTSD, depression, and comorbid PTSD/depression following traumatic injury. METHOD: A group of 363 injury survivors was assessed just prior to discharge from hospital and 3 and 12 months postinjury. Canonical correlations were used to examine the relationship between PTSD and depression symptom severity and a set of predictor variables. Multinomial logistic regression was used to identify whether the diagnostic categories of PTSD, depression, and comorbid PTSD/depression were associated with different groups of predictors. RESULTS: The majority of psychopathology in the aftermath of trauma was best conceptualized as a general traumatic stress factor, suggesting that when PTSD and depression occur together, they reflect a shared vulnerability with similar predictive variables. However, there was also evidence that in a minority of cases at 3 months, depression occurs independently from PTSD and was predicted by a different combination of variables. CONCLUSIONS: While PTSD and comorbid PTSD/depression are indistinguishable, the findings support the existence of depression as a separate construct in the acute, but not the chronic, aftermath of trauma.