The contribution of pain, reported sleep quality, and depressive symptoms to fatigue in fibromyalgia

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Abstract
The major objective of this research was to evaluate the predictors of fatigue in patients with fibromyalgia (FM), using cross-sectional and daily assessment methodologies. In the cross-sectional phase of the research involving a sample of 105 FM patients, greater depression and lower sleep quality were concurrently associated with higher fatigue. While pain was correlated with fatigue, it did not independently contribute to fatigue in the regression equation. For a subset of patients from the cross-sectional sample ( n =63) who participated in a week of prospective daily assessment of their pain, sleep quality, and fatigue, multiple regression analysis of aggregated (averaged) daily scores revealed that previous day's pain and sleep quality predicted next day's fatigue. Depression from the cross-sectional phase was not related to aggregated daily fatigue scores. A path analytic framework was tested with disaggregated (removing between subjects variability) data in which pain was predicted to contribute to lower sleep quality which, in turn, was predicted to lead to greater fatigue. The results revealed that poor sleep quality fully accounted for the positive relationship between pain and fatigue, thus substantiating the mediational role of sleep quality. The findings are indicative of a dysfunctional, cyclical pattern of heightened pain and non-restful sleep underlying the experience of fatigue in FM.