Background: Chronic fatigue syndrome (CFS) is a heterogeneous condition. A few studies have shown that some independent factors predict outcomes after cognitive behaviour therapy (CBT). Two recent systematic reviews suggest that heterogeneity may moderate treatment outcomes. However, no study has explored whether subgroups of CFS predict response to treatment. Methods: We used both latent class analysis (LCA) and latent class regression (LCR) to clarify the relationship between subgroups of CFS patients (n = 236), diagnosed using the Oxford diagnostic criteria, and the response to CBT. We measured symptoms, demographics, mood, and cognitive and behavioural responses to illness to define subgroups. Results: We found 5 latent classes by LCA, which did not differ in the direction of their response to CBT, with all classes showing improvement. In contrast, an exploratory LCR identified 4 latent classes, 1 of which predicted a poor response to CBT, whereas the other 3 predicted a good outcome, accounting for more than 70% of the patients. The negative outcome class was defined by weight fluctuations and physical shakiness, anxiety, pain and being focused on symptoms. Conclusions: CBT should be offered to all classes of patients with CFS, when defined by these measures. It may be possible to predict a minority group with a negative outcome, but this exploratory work needs replication.

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