Characteristics associated with physical functioning and fatigue in patients with chronic fatigue syndrome (CFS): secondary analyses of a randomized controlled trial

Objective: This study aimed to explore associations at the group level between patient characteristics at baseline and the outcomes of physical functioning and fatigue in patients with chronic fatigue syndrome (CFS) participating in a randomized controlled trial on cognitive behavioural therapy (CBT).Methods/design: Consecutively, 236 adult participants fulfilling the Centres for Disease Control and Prevention (CDC) 1994 criteria for CFS were randomly allocated to either 16 weeks of standard CBT, 8 weeks of Interpersonal CBT or a treatment as usual control group. In secondary analyses we investigated how gender, age, pain, anxiety, depression, memory and VO2max at baseline were associated with physical function and fatigue before and after treatment, controlling for the CBT-interventions and the baseline levels of the outcome measures. For the two groups receiving CBT, a 1-year follow-up analysis was also done. Bivariate and multivariable linear regression was used to explore the targeted associations.Results: At baseline, less pain (p < .001) and higher VO2max (p = 0.014) were associated with better physical function, while better memory (p = 0.001) and fewer depressive symptoms (p = 0.017) were associated with less fatigue. Better memory and physical function at baseline (p = 0.015 and p < .001, respectively) and male gender (p = 0.003) were associated with higher physical function post-intervention. Male gender (p = 0.010) was associated with higher physical function at 1-year follow-up. Fatigue severity at baseline was the only variable associated with follow up scores for fatigue (p < .001).ConclusionOur findings show that fatigue and physical function were associated with different types of characteristics at baseline, indicating a heterogeneity among CFS patients.