Usefulness of multiple dimensions of fatigue in fibromyalgia.

OBJECTIVES To explore in which contexts ratings of multiple dimensions of fatigue are useful in fibromyalgia, and to compare multidimensional fatigue between women with fibromyalgia and healthy women. DESIGN A cross-sectional study. SUBJECTS AND METHODS The Multidimensional Fatigue Inventory (MFI-20), comprising 5 subscales of fatigue, was compared with the 1-dimensional subscale of fatigue from the Fibromyalgia Impact Questionnaire (FIQ) in 133 women with fibromyalgia (mean age 46 years; standard deviation 8.6), in association with socio-demographic and health-related aspects and analyses of explanatory variables of severe fatigue. The patients were also compared with 158 healthy women (mean age 45 years; standard deviation 9.1) for scores on MFI-20 and FIQ fatigue. RESULTS The MFI-20 was associated with employment, physical activity and walking capacity (rs = -0.27 to -0.36), while FIQ fatigue was not. MFI-20 and FIQ fatigue were equally associated with pain, sleep, depression and anxiety (rs = 0.32-0.63). Regression analyses showed that the MFI-20 increased the explained variance (R2) for the models of pain intensity, sleep, depression and anxiety, by between 7 and 29 percentage points, compared with if FIQ fatigue alone was included in the models. Women with fibromyalgia rated their fatigue higher than healthy women for all subscales of the MFI-20 and the FIQ fatigue (p < 0.001). CONCLUSION Dimensions of fatigue, assessed by the MFI-20, appear to be valuable in studies of employment, pain intensity, sleep, distress and physical function in women with fibromyalgia. The patients reported higher levels on all fatigue dimensions in comparison with healthy women.