A register-based, epidemiological evaluation of disease activity and functional performance in ankylosing spondyloarthritis patients after multimodal spa therapy in Austria

Introduction Evidence regarding the impact of multimodal treatment on disease activity and functional performance in ankylosing spondyloarthritis (AS) remains scarce. This study aims to evaluate changes in these outcomes after multimodal rehabilitation including low-dose radon, using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Functional Index (BASFI). Methods Mixed-effects linear regression was performed on prospectively collected registry data to explore associations between timepoints and BASDAI/BASFI. Predicted linear margins from fixed effects were calculated for each timepoint. Data were derived from AS patients who underwent multimodal rehabilitation and completed questionnaires at baseline (T0), post-intervention (T1), and at 3 (T2), 6 (T3), and 9 (T4) months follow-up. Results Two hundred fifty-seven AS patients were included (52.14 ± 10.20 years; 42.57% female, BMI: 26.64 ± 4.27 kg/m 2 ). Compared to baseline, BASFI/BASDAI improved significantly until 6 and 9 months, respectively. Predicted BASDAI scores at T0, T1, T2, and T3 were 2.99 (95%CI 2.77; 3.21), 2.31 (2.08; 2.53), 2.38 (2.15; 2.61), and 2.69 (2.46; 2.92). At T4 the score was higher than at T0 (3.04 (2.81; 3.28)). Compared to T0, BASDAI score at T1 reflected a clinically relevant change. Predicted BASFI scores at T0, T1, T2, T3, and T4 were 4.09 (3.88; 4.31), 2.71 (2.49; 2.94), 2.83 (2.60; 3.06), 3.24 (3.01; 3.46), and 3.59 (3.36; 3.82). Compared to T0, BASFI scores at T1, T2, and T3 reflected a clinically relevant change. Conclusion Significant improvements in physical functioning and disease activity among AS patients following multimodal rehabilitation including low-dose radon were found. Such interventions may serve as a valuable complement to pharmacological treatment.