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Two studies suggest that reductions in posttraumatic symptoms (Aderka et al., 2013) and cognitions (Zalta et al., 2014) precede reductions in depressive symptoms during prolonged exposure (PE) therapy for posttraumatic stress disorder (PTSD) in female assault survivors. The present study explored the temporal relationship between posttraumatic and depressive symptoms in a randomized trial of D-Cycloserine (DCS) versus placebo augmented virtual reality exposure (VRE) therapy for chronic World Trade Center-related PTSD following the September 11, 2001 terrorist attacks. Twenty-five male and female participants were randomly assigned to receive either 100 mg DCS (N = 13) or placebo (N = 12) 90 min before 12 weekly VRE sessions. Participants contributed a total of 280 weekly PTSD Checklist (PCL; Weathers et al., 1993) and Beck Depression Inventory-second edition (BDI-II; Beck et al., 1996) symptom scores. Two sets of mediation analyses for longitudinal mixed models assessed the effects of 1) lagged PCL on BDI-II (Model 1), and 2) lagged BDI-II on PCL (Model 2) in the VRE-DCS and VRE-Placebo treatment groups, respectively. Results revealed reciprocal relations between posttraumatic and depressive symptoms during VRE treatment, although reductions in posttraumatic symptoms led to subsequent reductions in depressive symptoms to a greater extent than the converse. These effects were stronger in the DCS-enhanced group. Findings suggest that VRE primarily decreases posttraumatic symptoms, which in turn leads to decreased depressive symptoms, and that DCS may strengthen these effects.

This study investigated rates of subthreshold PTSD and associated impairment in comparison to no PTSD and full PTSD and prospectively followed the course of subthreshold symptoms over 3 years. 3360 workers dispatched to the WTC site following 9/11 completed clinician interviews and self-report measures at three time points each one year apart. At Time 1, 9.7% of individuals met criteria for subthreshold PTSD. The no PTSD, subthreshold PTSD, and full PTSD groups exhibited significantly different levels of impairment, rates of current MDD diagnosis, and self-reported symptoms of depression. At Time 2, 29% of the initial sample with subthreshold PTSD continued to meet criteria for subthreshold or full PTSD; at Time 3, this was true for 24.5% of the initial sample. The study lends credence to the clinical significance of subthreshold PTSD and emphasizes that associated impairment may be significant and longstanding. It also confirms clinical differences between subthreshold and full PTSD.