0925 A Multilevel Time-lagged Mediation of Nightmare and PTSD Symptom Severity Across Time in a Combined Treatment

Abstract Introduction This study sought to contribute to understanding the role of sleep disturbances as a potential hallmark of PTSD through examining the relationship between changes in post-trauma nightmare (PTNM) severity (nightmare frequency and distress) and symptoms of PTSD over time during a combined treatment for PTSD and PTNMs. Methods Individuals diagnosed with PTSD and having at least weekly nightmares (n = 84) were randomized into one of three treatment conditions: 12-session Cognitive Processing Therapy (CPT) only (n = 31), CPT followed by 5-session Exposure, Relaxation, and Rescripting Therapy (ERRT) condition (n = 29; CPT+ERRT), or ERRT followed by CPT (n = 24; ERRT+CPT). Multilevel time-lagged mediation models were analyzed to examine if nightmare severity (frequency and distress) measured at an earlier time point (t1; baseline, week 6, week 12) mediated the change in PTSD symptom severity at a later time point (t2; week 6, week 12, or week 17). The reverse relationship was also explored. An exploratory aim focused on examining if the order of treatment (CPT+ERRT or ERRT+CPT) moderated the mediated relationships. Results Across all three treatment conditions, there were statistically significant reductions in PTSD symptom and nightmare severity over time. In the unmoderated mediation models, there were no significant indirect effects detected. When treatment order was included as a moderator, there was a conditional effect of treatment order on the indirect effects of time on nightmare severity at t2 through PTSD symptom severity at t1. Only in the ERRT+CPT condition was there a statistically significant negative relationship of time on nightmare and PTSD symptom severity at t1 (ps .05). Furthermore, only in the ERRT+CPT condition, there was a statistically significant negative relationship between nightmare severity at t1 and PTSD symptom severity at t2. Therefore, only in the ERRT+CPT condition did PTSD symptom severity at t1 mediate the relationship between time and nightmare severity at t2. Conclusion These results suggest that earlier increases in PTSD symptom severity are an important mediator of change for the improvement of nightmares specific to receiving ERRT first. Clinicians may glean insight from this study that can impact shared decision making with patients on treatment planning. Support (if any)