Efficacy of Acceptance and Commitment Therapy (ACT) in Group in Fibromyalgia

The main objective is to assess the efficacy of Acceptance \& Commitment Therapy (ACT) in group for the treatment of fibromyalgia. The secondary aims are: 1.- To assess the cost-effectiveness of ACT and 2.- To assess the efficacy of ACT in other variables such as anxiety, depression, pain or global function. 3.- To evaluate the usefulness or electroencephalographic cordance as a prognostic variable of the treatment. HYPOTHESIS: ACT in group is effective for improvement of pain acceptance and other outcome variables (pain, anxiety, depression, global function) in fibromyalgia, and it is cost-effective. Cordance is an useful predictor of treatment efficacy in these patients. DESIGN: Multicentre, randomized, controlled study, with parallel groups, and a 6-month follow-up period. Participants will be randomly allocated to one of two conditions: 1.- Group Acceptation \& Commitment Therapy or 2.- Treatment as usual by his general practitioner. Patients diagnosed of fibromyalgia, according to the American College of Rheumatology, will be recruited in primary care. Assuming an alpha=0.05 and p=80%, using two tails, and calculating 5% of refusals, it will be necessary a sample size of 55 patients for each group of patients.