Predictors and mediators of outcome in CBT for chronic pain : The roles of psychological flexibility and PTSD

Chronic pain is a commonly occurring and debilitating condition, and among the costliest health problems for both the individual and society at large. Cognitive behavioral therapy (CBT) is the most widely-disseminated psychological treatment for chronic pain. Even though it is recommended and evidence-based, it yields quite modest improvements in pain-related functioning and accompanying symptoms of emotional distress. It is now generally acknowledged that further efforts are needed to improve the efficacy of CBT for chronic pain. Specifically, pain researchers have called for studies to identify mechanisms that underlie changes in treatment outcomes (mediators) and characteristics of the individual that predict improvements in these mechanisms and treatment overall (predictors and moderators). To address this call, the primary aim of this research program was to study whether changes in psychological flexibility mediated outcomes in a multi-disciplinary, group-based CBT program delivered at a regional specialist unit for pain rehabilitation. The secondary aim was to identify possible predictors of outcome by focusing on facets of psychological flexibility as well as the understudied influence of posttraumatic stress disorder (PTSD). This aim also included investigation of the relationships between PTSD, pain presentation, and psychological flexibility. With these two aims, we hoped to shed further light on the validity of the psychological flexibility model as an integrating, overarching model that can help define relevant treatment processes for adults presenting with chronic pain and psychiatric problems. Study I investigated whether pain-related acceptance, from the psychological flexibility model, and other variables posited as potential mediators in standard CBT mediated changes in pain-related outcomes measured at post-treatment and 12-month follow-up from the CBT program. The results highlighted the mediating role of pain-related acceptance across different indices of outcome.Study II evaluated the psychometric properties of the Swedish-language versions of the full length and shortened version of the Committed Action Questionnaire, as well as the generalizability of previous results related to committed action. The results supported the validity and reliability of the Swedish-language versions of the measure, the generalizability of earlier findings, and the relevance of committed action to health and functioning in individuals with chronic pain.Study III focused on the prevalence of traumatic experiences, trauma types, and PTSD in patients referred for treatment of chronic pain, and the relationship between PTSD and pain-related functioning prior to treatment. High rates of traumatic exposure and PTSD were found for chronic pain patients. The presence of PTSD in these patients was associated with worse clinical characteristics and an increased need for treatment.Study IV examined whether various processes from the psychological flexibility model mediated the relationship between PTSD and chronic pain. Results indicated that the relationship was mediated by pain-related acceptance, committed action, and cognitive fusion, where pain-related acceptance constituted the most influential mediator from the psychological flexibility model. Study V analysed whether indices of emotional distress (including PTSD) and different facets of psychological flexibility predicted pain-related outcomes at 12-month follow-up from the CBT program. Furthermore, it examined whether changes in processes from the psychological flexibility model mediated changes in pain-related outcomes. The only significant predictors of outcomes turned out to be psychological inflexibility and committed action. All available facets of psychological flexibility had mediating effects on treatment outcomes.Based on the results from these studies, theoretical integration within the CBT field may be facilitated by a process-focused approach including the psychological flexibility model. This model seems to be transdiagnostically and trans-situationally applicable in several ways. Its processes span problem areas with diverse backgrounds from the somatic field and chronic pain to the psychiatric field and PTSD, and appear useful not only to treatments specifically built around targeting psychological flexibility but also more broadly in CBT treatments