Does depression mediate the relation between fatigue severity and disability in chronic fatigue syndrome sufferers?

OBJECTIVE: Chronic fatigue syndrome (CFS) is often associated with significant levels of disability. Although fatigue and depression have been found to be independently related to severity of disability, it is not clear how these three factors are mutually related. The present study sought to address this issue by specifically testing a model of mediation whereby depression was hypothesized to influence relations between fatigue and disability.
METHODS: Participants included 90 individuals seeking treatment for CFS at a tertiary care facility. Each provided demographic information and completed standardized measures of depression and fatigue severity, as well as a measure of disability, which assessed difficulties in physical, psychosocial, and independence domains.
RESULTS: Analyses indicated that depression and fatigue were positively correlated with one another, as well as all three disability domains. Analyses of mediation indicated that depression completely mediated the relation between fatigue and psychosocial disability and partially mediated the relation between fatigue and the other two disability domains. Indirect effects tests indicated that the inclusion of depression in the statistical models was statistically meaningful.
CONCLUSIONS: These results replicate previous findings that fatigue and depression are independently related to disability in those with CFS. A more complex statistical model, however, suggested that depression severity substantially influenced the strength of the relation between fatigue and disability levels across a range of domains, including complete mediation in areas involving psychosocial functioning. These results may aid in clarifying contemporary conceptualizations of CFS and provide guidance in the identification of appropriate treatment targets.