FM is a common problem with substantial negative consequences. The most widely evaluated psychological treatment for FM is T-CBT which usually has small to moderate controlled effects on pain, mood and functional impairment. Based on one pilot study and one wailist-controlled RCT, Exp-CBT appears to have promising effects on FM but this treatment has not yet been compared to an active control condition. The present study aims to compare internet-delivered Exp-CBT to internet-delivered T-CBT in a randomized controlled trial.
Participants in Exp-CBT and T-CBT are encouraged to work with self-help texts and complete regular homework exercises via a secure treatment platform. Both treatments are 10 weeks long, equally exhaustive, and involve approximately the same level of therapist support.
Primary outcome is the relative effect of Exp-CBT and T-CBT on FM severity as modelled using linear mixed models fitted on weekly Fibromyalgia Impact Questionnaire sum scores over the treatment period, testing the hypothesis of Exp-CBT superiority based on the coefficient for the time × group interaction. The investigators will also calculate the number of treatment completers in each treatment condition, defined as having commenced module five out of eight treatment modules. Detailed information regarding analysis of clinical efficacy is provided in the supplementary file.
In addition to clinical efficacy, the investigators will also investigate cost-effectiveness and mediational processes. The primary hypothesis is that Exp-CBT is significantly more efficacious than T-CBT in reducing FM severity, i.e., the Fibromyalgia Impact Questionnaire (FIQ) composite score indicative of symptoms and functional status, from the baseline assessment to the 10-week assessment.