The effectiveness of cognitive behavioural therapy in groups for patients with Chronic Fatigue Syndrome (CFS): a randomised controlled study

INTERVENTION: After a basline assessment patients are randomly assigned to one of three conditions. There are two treatment conditions: small group (four patients and one therapist) and large group (eight patients and two therapists). Both group treatments consist of 16 sessions of two hours in a period of about six months. There is a second assessment after the treatment. The third condition is a waiting list condition. After the waiting period of at least six months, patients get a second assessment. CONDITION: Chronic Fatigue Syndrome (CFS) ; Nervous System Diseases ; Disorders of the brain PRIMARY OUTCOME: 1. Fatigue severity (measured with the CIS subscale fatigue severity).; 2. Disabilities (measured with the Sickness Impact Profile (SIP) total score and the Short form health survey (SF‐36) subscale 'physical functioning'). The CIS‐f, SIP and SF‐36 are used in two assessments, a baseline and a post‐treatment (or post‐waiting list) assessment. The change score between post‐treatment and baseline of each of the treatment conditions is compared with the difference score between post‐waiting list and baseline assessment of the waiting list condition. SECONDARY OUTCOME: Psychological distress measured with the Symptom Checklist 90 (SCL 90). INCLUSION CRITERIA: 1. Over 18 years old 2. Being able to speak and read Dutch 3. Meeting the 1994 research criteria for CFS as formulated by the US Center for Disease Control 4. Severely fatigued (having a Checklist Individual Strength (CIS)‐fatigue severity score of more than or equal to 35) 5. Severely disabled (weighted total score on the Sickness Impact Profile of more than or equal to 700) 6. Motivated for treatment of CFS with CBT 7. Having functioned good in groups before (self‐report) and willing to follow a group treatment for CFS 8. Given written informed consent for participation in the study