The role of anxiety and depression in fatigue and patterns of pain among subgroups of fibromyalgia patients.

This study explored the relationship of anxiety and depression with two major symptoms of fibromyalgia, pain and fatigue, among fibromyalgia patients (N = 322). Due to collinearity between anxiety and depression scores, extreme groups were defined according to high versus low anxiety and depression scores. Two-thirds of the initial sample were excluded by this approach, which permitted a two by two factorial split-plot ANOVA for the assessment of main effects and the interaction of anxiety and depression upon pain and fatigue. Results stated independent, additive, effects of anxiety and depression upon levels of pain and fatigue, whereas interaction between anxiety and depression failed to significantly explain symptom differences among the participants. Correlational analyses indicated widespread pain among the low anxiety subgroups. In contrast, widespread pain was not indicated among anxious patients with low scores on depression. The findings support the hypothesis that (1) anxiety and depression are independently associated with severity of pain symptoms in fibromyalgia, and that (2) patients with high anxiety and low depression may communicate to the medical doctor in ways that involve a risk of diagnosing fibromyalgia when the criterion of widespread pain is not supported. These conclusions were confirmed by results from ANCOVAs that permitted more extensive control of collinearity among variables.