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The aim of this study was to evaluate the psychometric properties of the Danish version of the Fibromyalgia Impact Questionnaire - Revised (FIQR), when used to quantify the severity of disease burden in a Danish population of patients with chronic widespread pain (CWP), including fibromyalgia (FM).A total of 924 participants diagnosed with CWP and/or FM completed an electronic version of the FIQR via touchscreens in the clinic at referral for specialist care. Data were collected from 1 January 2018 to 3 September 2020. Rasch measurement methods were applied.Rating scale analysis suggested multiple threshold disordering in the 0-10 category rating scale. A principal component analysis suggested assessment of a multidimensional construct. Thus, the Rasch analysis of the full FIQR was discontinued. Instead, Rasch analyses were performed on the two subscales: 'function' and 'symptoms'. By collapsing the rating scale to a 0-4 category scale, the remaining threshold disordering of both subscale was solved. Only the symptom subscale indicated multidimensionality. There was underfitting misfit of item 21 and overfitting misfit of item 12. No significant differential item functioning, defined by sex, ethnicity, or education, was found.The FIQR should be considered as an instrument consisting of three separate subscales representing 'function', 'overall impact', and 'symptoms'. We recommend calculating and reporting on both a 0-10 and a 0-4 category scale. Also, if using the total FIQR score as an outcome measure, this should be done with caution, until revision of the rating scale.

Background: Assessment of depression in chronic pain patients by self-rating questionnaires developed and validated for use in normal and/or psychiatric populations is common. The aim of this study was to evaluate the psychometric properties of the Major Depression Inventory (MDI) in a sample of females with chronic widespread pain (CWP).Method: A total of 263 females diagnosed with CWP and referred for rehabilitation completed the MDI as part of the baseline evaluation. Rasch analysis was applied to this dataset. Rasch measurement models allow detailed analyses of an instruments rating scale and further aspects of validity, including fit of individual scale items to a unidimensional model indicating assessment of a single construct (depression), as a prerequisite for measurement.Results: The Rasch analysis revealed substantial problems with the rating scale properties of the MDI and lack of unidimensionality. In contrast to somatic items, MDI items related to depressed mood and negative view of oneself were distributed at the higher end of the item difficulty measurement scale, indicating low endorsement of these items.Discussion: From the perspective of the Rasch measurement model, the MDI demonstrated insufficient psychometric properties when used to identify and quantify severity of depression in a clinical sample of females with CWP. The observed item endorsement pattern indicated that, in this study population, the relatively high depression severity scores primarily pertained to a common core of pain-related somatic symptoms. Careful consideration when interpreting questionnaire-derived scores of depression implemented in research and routine clinical care of patients with chronic pain is warranted.

OBJECTIVES: To compare the 28-joint Disease Activity Score (DAS28) and its components in patients with rheumatoid arthritis (RA) with and without concomitant fibromyalgia (FM), and to investigate the use of biological treatment in the two groups.METHOD: Questionnaires developed to diagnose FM were handed out among RA patients during their planned visits. Values for DAS28 were obtained from the DANBIO registry. Demographic data and data on patients' medical treatment, disease duration, serological and radiological status were retrieved from patients' files. The χ(2) test and an unpaired t-test were applied to investigate group differences in the use of biological therapy, baseline characteristics, patient-reported outcomes, and DAS28 between groups when appropriate.RESULTS: Questionnaires were completed by 162 out of 264 (61%) patients. Twenty-five patients (15.4%) with concomitant FM were identified. No group differences were found regarding disease duration, age, gender, and serological status. Of the RA patients with concomitant FM, 64% were treated with biological therapy vs. 32% of RA patients without concomitant FM (p = 0.002). The mean DAS28 in the FM group was 4.4 compared to 2.9 in the non-FM group (p < 0.001). Elevated DAS28 in the FM group resulted from a high tender joint count (p = 0.003) and a high visual analogue scale (VAS)-global score (p < 0.001). Erosions were more frequent in the non-FM group (p = 0.04).CONCLUSIONS: Concomitant FM in patients with RA is associated with a higher DAS28 due to subjective parameters and with the more frequent use of biological treatments. This raises the question of whether the more frequent use of biologics in these patients is justified by inflammation, or is instead due to persistent pain and other centrally mediated symptoms.