Comparison between different health state utility instruments in patients with fibromyalgia.

Background: Cost-utility analysis uses utility indexes to assess treatment effects. Some discrepancies between different utility indexes instruments are suggested and need to be identified in health conditions not yet investigated.

Objective: To compare different utility indexes instruments in Brazilian patients with fibromyalgia and identify variables associated with these instruments.

Methods: Impact of fibromyalgia (Fibromyalgia Impact Questionnaire [FIQ]) and utility indexes (Short-Form 6 Dimensions [SF-6D], EuroQol 5 Dimensions [EQ-5D], and EuroQol - Visual Analogue Scale [EQ-VAS]) were assessed in 97 patients with fibromyalgia at baseline, 8-week (after an exercise-based intervention), and 6- and 12-month follow-up. Construct validity and responsiveness of the utility indexes instruments were compared. Multiple regression models were used to verify the variables associated with the utility indexes instruments.

Results: Construct validity analysis showed that FIQ presented moderate correlation with the SF-6D, the EQ-5D, and the EQ-VAS (r=-0.43, -0.41, -0.30, respectively, all p < .01). There was a moderate correlation between the SF-6D and the EQ-5D (r = 0.51, p < .001), moderate correlation between the SF-6D and the EQ-VAS (r = 0.41, p < .001), and no correlation between the EQ-VAS and the EQ-5D. The EQ-5D was responsive at the 8-week and 6-month follow-up, the SF-6D was responsive only at 6-month follow-up and the EQ-VAS was not responsive. The FIQ was associated with the EQ-5D and the SF-6D indexes, and symptom duration and depression with the EQ-VAS index.

Conclusion: The EQ-5D better assessed the clinical change in patients with fibromyalgia. Furthermore, impact of fibromyalgia, symptom duration, and depression seem to be associated with the utility indexes.