Background/Purpose: Currently, only limited information is available on the long-term course of limitations in physical functioning and spinal mobility in Ankylosing Spondylitis (AS) patients receiving TNF inhibiting (TNFi) therapy in daily clinical care. Therefore this study aimed (i) to examine the 3-years course of physical functioning and spinal mobility impairments in patients routinely treated with TNFi; (ii) to predict the 3-years level and (iii) to predict the 3-years course of physical functioning and spinal mobility.

Methods: AS patients eligible for TNFi were followed in a prospective observational cohort for 3 years. Prediction models were developed with linear mixed modelling using 18 baseline variables. The Bath AS Functional Index (BASFI) and Bath AS Metrology Index (BASMI) were used as outcome measures for physical functioning and spinal mobility, respectively.

Results: At baseline 257 patients were included and treated with etanercept (n=174) or adalimumab (n=83). Physical functioning improved significantly during the first 24 weeks after the start of TNFi. The BASFI score decreased from 5.4±2.4 to 3.3±2.6 in week 24, and stabilised thereafter (BASFI 3-years 3.6±2.5; see figure-1). The BASMI showed a stable course over time. Lower baseline BASFI and BASMI-scores predicted a better physical functioning and spinal mobility after 3-years of TNFi therapy. Other predictors for a higher 3-years level and better 3-years course of physical functioning included absence of comorbidity, physical activity, younger age and lower body mass index (BMI) at baseline. However, large between-patient variations were observed.

Conclusion: Improvement of physical functioning in TNFi treated AS patients continues up to 24-weeks and stabilises thereafter. Therefore, the efficacy of treatment should be determined at 6 months. Predictors for the level and course of physical functioning and spinal mobility after 3-years of TNFi treatment include baseline BASFI, BASMI, absence of comorbidity, physical activity and BMI.