Background A discrepancy between subjective (i.e., patients' perceptions) and objective (i.e., clinical observations) of physical function (PF) has been reported in fibromyalgia (FM). This discordance, with a worse subjective PF than objective PF, may have negative consequences for health-related outcomes such as the ability to pursue valued activities in daily life. Therefore, it seems important to find modifiable factors associated with this discrepancy between objective and subjective PF in FM.
Objectives The present cross-sectional study examined 1) the existence of discordance between subjective and objective PF, 2) the independent association of catastrophizing and self-efficacy with subjective and objective PF, and 3) the independent association of catastrophizing and self-efficacy with the discrepancy between subjective and objective PF.
Methods A total of 427 FM women filled out the Pain Catastrophizing Scale, Chronic Pain Self-efficacy Scale, and PF subscales of the SF-36 (SF-36-PF) and of the Revised FM Impact Questionnaire (FIQ-R-PF). Objective PF was measured by performance-based tests: the Senior Physical Fitness Test Battery plus handgrip strength test. Subjective and objective PF were transformed to standardized z-scores ([value-mean]/standard deviation; using means and standard deviations of a general population sample, n=230). These scores reflect the deviation of FM patients from the general population in standard deviation units.
Results In one-way analysis of variance (ANOVA), subjective PF was poorer than objective PF (P<.001). Linear regression analysis (adjusted by age, body mass index, years since FM diagnosis, and educational level) showed that high pain catastrophizing and low self-efficacy were independently associated with high subjective and objective PF. Linear regression analysis revealed that high pain catastrophizing (for SF-36-PF and FIQ-R-PF) and low self-efficacy (for the SF-36-PF) were associated with a greater discrepancy between subjective and objective PF.
Conclusions Subjective PF is worse than objective PF in FM. High catastrophizing and low self-efficacy are not only independently associated with low subjective and objective PF but also with a greater discordance between subjective and objective PF in FM. Our findings suggest that clinical trials that combine cognitive therapy (focused on increasing subjective PF and self-efficacy and reducing catastrophizing) and physical exercise (focused on enhancing objective PF) have potential to be effective in FM.
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Acknowledgement This study was funded by the Spanish Ministries of Economy and Competitiveness [I+D+I DEP2013–40908-R, I+D+I DEP2010–15639, BES-2014–067612 and BES-2011–047133] and Education [FPU12/00963 and FPU14/12518]. VAA was supported by the Andalucía Talent Hub Program launched by the Andalusian Knowledge Agency, co-funded by the European Union's Seventh Framework Program, Marie Skłodowska-Curie actions (COFUND – Grant Agreement No. 291780) and the Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía.
Disclosure of Interest None declared