Objectives: The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Dougados Functional Index (DFI) are the most commonly used instruments to measure disease activity and functioning in ankylosing spondylitis (AS). The aim of this study was to translate, adapt and validate these instruments into the Spanish language.
Methods: The BASDAI, BASFI, and DFI questionnaires were translated into Spanish by three independent bilingual physicians who were familiar with the medical aspects of AS and by one professional translator. Two rheumatologists familiar with instrument validation, and who were aware of the purpose of the study, examined semantic, idiomatic and conceptual issues and produced by consensus unified versions of each instrument. English back-translations from the Spanish were done by a professional translator unaware of the original version. Both English versions were compared, and where needed, modifications to the Spanish versions were made. The Spanish versions were administered to 61 ambulatory patients with AS and to 80 patients with undifferentiated spondyloarthropathy for validation purposes. Reliability and responsiveness were measured in 28 patients participating in a physiotherapy program.
Results: Reliability showed an acceptable 24-hour test-retest intraclass correlation coefficient (ICC)--BASFI ICC: 0.68, 95% CI: 0.29-0.85; BASDAI ICC: 0.74, 95% CI: 0.52-0.88 and DFI ICC: 0.87, 95% CI: 0.73-0.94. The construct validity of the instruments was evaluated, and BASDAI was correlated with disease activity measured by the total enthesis count (rs: 0.34); general well being in the last week (rs: 0.7); spinal pain (rs: 0.53) and duration of morning stiffness (rs: 0.64). BASFI correlated with Schöber's test (rs: -0.4); occipital-wall distance (rs: 0.38) and thoracic expansion (rs: -0.3). DFI correlated with Schöber's test (rs: -0.36); occipital-wall distance (rs: 0.29) and chest expansion (rs: -0.3). The correlation among DFI and BASFI was rs: 0.83. All instruments showed clinical responsiveness in the physiotherapy program (baseline and end of program; mean +/- SD): BASDAI: 6.25 +/- 1.97 and 3.07 +/- 2.04 (p = 0.0001); BASFI: 5.68 +/- 2.29 and 2.88 +/- 1.77 (p = 0.0001); DFI: 16 +/- 7.6 and 8.0 +/- 5.5 (p = 0.001) with effect sizes and standardized effect sizes > 1.
Conclusions: The Mexican Spanish versions of the BASDAI, BASFI, and DFI showed adequate reliability, validity and responsiveness to clinical change. These instruments can be used in the clinical evaluation of Spanish-speaking patients with AS.