To translate, adapt, validate and assess the sensitivity to change of a Spanish version of the Fibromyalgia Impact Questionnaire (FIQ-S).
The FIQ-S was adapted following the translation and back-translation methodology. Female patients with fibromyalgia (FM) were invited to participate. Reliability was analyzed by the Spearman correlation coefficient between test and retest. Internal consistency was checked by the Cronbach's alpha coefficient. Construct validity was analyzed comparing FIQ-S with: HAQ, FHAQ, SF-36, SCL90-R, and the visual analogue scale for pain. Sensitivity to change was assessed in an 8-week randomized trial of exercise therapy. Feasibility was analyzed by the time taken in completing the FIQ-S and the proportion of patients able to complete the questionnaire.
Translation was concordant. Adaptation affected at 4 sub-items of physical function. One-hundred and two FM patients completed the protocol. Mean age was 48.7 years with a mean of 9.2 years of evolution. Test-retest correlations were between 0.61-0.85 (p < 0.0001). Internal consistency showed alpha = 0.82 for all items and alpha = 0.86 for the sub-items of physical function. Significant correlations (p < 0.0001) were found between the FIQ-S items and HAQ, FHAQ, SF-36 and SCL90-R. For patients treated with the exercise program, the pre-treatment FIQ-S score was 52.0 +/- 11.5 and the post-treatment score was 40.8 +/- 13.7 (p < 0.003). Mean time for completing FIQ-S was 3.3 minutes. In 4% of the patients external help was needed.
The FIQ-S is a reliable, valid and responsive to changes questionnaire for measuring health status and physical function in Spanish speaking FM patients.