Latent Class Differences Explain Variability in PTSD Symptom Changes During Cognitive Processing Therapy for Veterans

Despite demonstrated effectiveness of cognitive-behavioral psychotherapies for posttraumatic stress disorder (PTSD), there is limited research on the trajectory of PTSD symptom change during the course of these therapies. In addition, existent findings are mixed, making it difficult to know how individuals' PTSD symptoms will change from week to week during psychotherapy. The study presented here uses general growth mixture modeling (GGMM) to test the hypothesis that multiple latent classes will explain individual differences in PTSD symptom change during the course of cognitive processing therapy (CPT). Participants were 207 U.S. military veterans with PTSD who received CPT through an outpatient Veterans Affairs PTSD treatment program. Participants were mostly male (89%), White (81%), and averaged 42 years old. The PTSD Checklist (PCL), Clinician-Administered PTSD Scale (CAPS), and the Beck Depression Inventory-II (BDI-II) were administered at pre- and posttreatment; the PCL was also administered weekly to assess PTSD symptom changes during CPT. GGMM showed that a quadratic growth model with three distinct latent classes best explained the trajectory of PTSD symptom reductions during CPT. The following variables significantly predicted latent class membership: age; ethnicity; having combat as the worst trauma; and pretreatment PCL, CAPS, and BDI-II scores. In turn, class membership significantly predicted posttreatment PCL, BDI-II, and CAPS scores. This study is novel in showing that latent class differences in PTSD symptom reductions are useful in explaining why individuals exhibit variable rates of PTSD symptom change during psychotherapy and differing outcomes after psychotherapy. These findings may improve the ability to more accurately anticipate individual differences in PTSD symptom changes and responses to psychotherapy.