The Complex Relationship between Pain Intensity and Physical Functioning in Fibromyalgia: The Mediating Role of Depression.

Purpose: Fibromyalgia (FM) is typically associated with the experience of diffuse pain and physical impairment. Depression also commonly co-exists in patients with FM, and has been correlated with pain intensity and physical functioning. Previous research suggests an association between pain intensity and physical functioning; however, the direct causal relationship between improvements in pain intensity and in functioning is not observed in many FM patients. This may suggest that another factor such as depression is mediating this relationship. The present work examined mediating role of depression.

Methods: 216 patients with FM completed measures of pain intensity, depression, and physical function as part of a larger longitudinal study. Assessments were completed at baseline, 12, 24, and 36 weeks.

Results: Longitudinal mediational analyses indicated that depression is a partial mediator of the relationship between pain intensity and physical functioning at all four assessment points. Beta coefficients for the path from pain to physical functioning ranged from 0.18 - 0.36, with attenuated path coefficients ranging from 0.03 - 0.08, still showing significant but decreased associations when depression was added as a mediator.

Conclusions: Clinical implication includes the importance of treating co-morbid depression in patients with fibromyalgia early in the course of treatment to prevent engagement in the cycle of disability.