Is the effect of cognitive behaviour therapy for chronic fatigue syndrome (ME/CFS) moderated by the presence of comorbid depressive symptoms? A meta-analysis of three treatment delivery formats.

Objective: Cognitive behaviour therapy (CBT) for fatigue in chronic fatigue syndrome (ME/CFS) leads to a significant reduction of fatigue and disability and is available in different treatment delivery formats, i.e. internet-based, individual face-to-face and group face-to-face. The aim of this study was to investigate whether moderation of the effects of CBT by clinically relevant depressive symptoms varies between CBT delivery formats.

Methods: Data from six randomised controlled trials (n = 1084 patients) were pooled. Moderation of clinically relevant depressive symptoms (Brief Depression Inventory for Primary Care) in different treatment formats on fatigue severity (Checklist Individual Strength, subscale fatigue severity), functional impairment (Sickness Impact Profile-8) and physical functioning (Short Form-36, subscale physical functioning) was investigated using linear mixed model analyses and interaction tests. Differences in percentages of patients no longer severely fatigued post-CBT were studied by calculating relative risks.

Results: The moderator effect of depressive symptoms on fatigue severity varied by delivery format. In internet-based CBT, ME/CFS patients with depressive symptoms showed less reduction in fatigue, and were more often still severely fatigued post-treatment than patients without depressive symptoms. In individual and group face-to-face CBT, no significant difference in treatment effect on fatigue severity was found between patients with and without depressive symptoms. No moderation was found for the other outcomes.

Conclusion: In internet-based CBT, ME/CFS patients with comorbid depressive symptoms benefit less, making face-to-face CBT currently the first-choice delivery format for these patients. Internet-based CBT should be further developed to improve its effectiveness for ME/CFS patients with depressive symptoms.