Comprehensiveness and validity of a multidimensional assessment of patients with fibromyalgia : a prospective cohort study

Background and aims: The aims of this study were to investigate the multidimensionality and characteristic traits of fibromyalgia and to examine the validity of single measurement scales used in a comprehensive, multidimensional assessment conducted before and after pain rehabilitation. Methods: Prospective cohort study using the Short Form 36 (SF-36), the Multidimensional Pain Inventory (MPI), the Symptom Checklist-90-Revised (SCL-90-R), the Fibromyalgia Health Assessment Questionnaire (FHAQ), the Fibromyalgia Impact Questionnaire (FIQ), and the 6-Minute-Walking-Distance (6MWD) and others. Comprehensiveness and overlap of the constructs were quantified by bivariate correlations, explorative factor analysis, and effect sizes. Results: Patients (n=123) were of 48.6 years and 86.2% female. Factor analysis revealed 2 factors with explained variances of 44.5%-64.5%. Cross-sectionally, mental health and psychosocial factors loaded more strongly on the first, mental health factor, especially the 4 SCL-90-R scales (loads 0.75-0.90) than on the second, predominantly physical function factor. Longitudinally, the physical function factor was dominant, with loads of 0.61 (FHAQ), 0.66 (6MWD), and SF-36 and MPI pain (0.68 each). Cross-sectional correlations were up to 0.89 between depression and anxiety, up to 0.87 between pain and interference on the MPI, and up to 0.83 between depression and catastrophizing. Longitudinally, all scales showed improvements. Conclusions: All 23 health parameters examined had moderate to high factor loads on at least one factor, evidence of the multidimensionality of fibromyalgia. Mental health and function were the 2 traits explaining the substantial, partially comparable variances of the clinical characteristics. A broad spectrum of constructs, including fatigue, somatization, and coping is needed to describe the fibromyalgia syndrome accurately.