Mediators of change in Acceptance and Commitment Therapy for pediatric chronic pain Rikard K. Wicksell a,b,⇑ , Gunnar L. Olsson a,c , Steven C. Hayes d a Behavior Medicine Pain Treatment Service, Astrid Lindgren Children’s Hospital, Karolinska University Hospital, Stockholm, Sweden b Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden c Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden d Department of Psychology, University of Nevada, Reno, NV, USA Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article. article info Article history: Received 17 February 2011 Received in revised form 24 August 2011 Accepted 8 September 2011 Keywords: Chronic pain Children Cognitive behavior therapy Acceptance and Commitment Therapy Mediation analysis Mechanisms of change abstract Even though psychological interventions are well established in the treatment of pediatric chronic pain, there is a clear need for further development, especially with severely disabled patients. However, opti- mizing effectiveness in psychological treatments for pain requires clarification of the mechanisms of action. Studies addressing change processes are scarce, however, particularly in relation to pediatric chronic pain. Acceptance and Commitment Therapy (ACT), as an extension of traditional cognitive behavior therapy, is essentially aimed at improving functioning by increasing the ability to act effec- tively in the presence of pain and distress, that is, psychological flexibility. ACT has shown promising results for both adult and pediatric chronic pain. In the present study, the mediators of change in an ACT-oriented treatment for pediatric chronic pain were examined using a bootstrapped cross product of coefficients approach. Pain interference and depression were used as outcome variables. Six different variables relevant to theories underlying ACT and cognitive behavior therapy were included in the anal- yses as possible mediators of change: pain impairment beliefs, pain reactivity, self-efficacy, kinesiopho- bia, catastrophizing, and pain intensity. Results illustrated that pain impairment beliefs and pain reactivity were the only variables that significantly mediated the differential effects of treatment on outcomes at follow-up. Also, these 2 mediators were shown to independently predict effects in out- come variables at follow-up while controlling for earlier effects in outcome, but only for the ACT con- dition. Although tentative, the pattern of results suggests that variables consistent with psychological flexibility mediate the effects of ACT-based interventions to improve functioning in patients with chronic debilitating pain. Ó 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. 1. Introduction Pediatric chronic pain is common [16,53], and can be associated with significant disabilities [25,29,51] that may continue into adulthood [5,78,80]. Psychological treatments, particularly cogni- tive behavior therapy (CBT), has proven useful for adults with chronic pain [15,24], but randomized controlled trials (RCT) with pediatric patients are still scarce [14,52]. Psychological treatment represents a wide variety of interventions with various objectives (eg, decreased pain and/or related distress, improved self-efficacy) [63]. Reductions in pain and distress have typically been the primary outcome variables, rather than increases in functional abilities [14,51,79]. Also, evaluations of such interventions have largely addressed effectiveness rather than the identification of change processes [69]. Thus, the processes through which psycho- logical treatments operate are still unclear [48], and the clarifica- tion of these change processes is considered a central target for current clinical research [15,31,32,52]. Although such studies have recently increased [36,57,65], process analyses of psychological treatments of pediatric pain are sparse. Recent research has illustrated that greater acceptance of chronic pain is associated with less avoidance of important activi- ties, better emotional well-being, and less health care utilization [41–43]. Furthermore, the empirical support for acceptance- oriented interventions, primarily Acceptance and Commitment Therapy (ACT) [22], has increased for both adult [44,46,82] and pediatric [83,85,86] chronic pain. ACT was recently listed by Divi- 0304-3959/$36.00 Ó 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.pain.2011.09.003 ⇑ Corresponding author at: Behavior Medicine Pain Treatment Service, Astrid Lindgren Children’s Hospital, Karolinska University Hospital, Stockholm 171 76, Sweden. Tel.: +46 0 8 517 79 917; fax: +46 0 8 517 77 265. E-mail address: Rikard.Wicksell@karolinska.se (R.K. Wicksell). www.elsevier.com/locate/pain PAIN Ò 152 (2011) 2792–2801