Development and validation of the self-administered Fibromyalgia Assessment Status: a disease-specific composite measure for evaluating treatment effect

IntroductionThe Fibromyalgia Effect Questionnaire (FIQ) is a composite disease-specific measure validated for fibromyalgia (FM), however it is seldom used in clinical practice. The objective was to generate and analyze the psychometric properties of a new composite disease-specific index (Fibromyalgia Assessment Status, FAS), a mild self-administered index that combines a patient's assessment of fatigue, sleep disturbances and pain evaluated on the argument of the 16 non-articular sites document of the Self-Assessment Pain Scale (SAPS) in a single measure (range 0 to 10). Methods: The FAS index was constructed using a traditional adulthood strategy, and its psychometric properties were tested in 226 FM patients (209 women, 17 men); whose disease-related characteristics were assessed by means of an 11-numbered hand-bill numerical assessing scale (NRS) for pain, fatigue, sleep disturbances and usual health (GH), the easily site score (TPS), the SAPS, the FIQ, and the SF-36. A chain of 226 rheumatoid arthritis (RA) patients was used for comparative purposes. Of the 179 FM patients who entered the follow-up study, 152 completed the 3-month interval and were included in the responsiveness analyses. One hundred and fifty-four patients repeated the FAS questionnaire after an interval of one week, and its test/re-test reliability was calculated. Responsiveness was evaluated on the rationale of effect amount and the standardised response mean. Results: The FAS index fulfilled the established criteria for validity, reliability and responsiveness. Factor debate showed that SAPS and tiredness contributed most, and respectively explained 47.4% and 31.2% of the variance; sleep explained 21.3%. Testing for internal consistency showed that Cronbach's alpha was 0.781, thus indicating a big level of reliability. As expected, closer eloquent correlations were found when FAS was compared with total FIQ (rho=0.347; P<0.0001) and the FIQ subscales, mainly labour ability, tiredness, fatigue and grief (all P<0.0001), on the contrary the correlation between FAS and the intellectual element abstract scale score (MCS) of the SF-36 (rho = -0.531; P<0.0001) was remarkably interesting. Test/re-test reliability was satisfactory. The FAS showed the greatest end product size. The dimensions of the responsiveness measures was statistically changed between FAS (0.889) and the FIQ (0.781) (P = 0.038), and between the SF-36 MCS (0.434) and the SF-36 physical component precis scale score (PCS) (0.321) (P<0.01). Conclusions: The self-administered FAS is a reliable, valid and responsive disease-specific composite measure for assessing treatment backlash in patients with FM.

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