Background There is a lack of observational studies exploring the long-term course of physical functioning in ankylosing spondylitis (AS) patients receiving TNF-inhibitors (TNFi) in daily clinical care.
Objectives To predict the 3 year course of physical functioning in AS patients routinely treated with TNFi in daily clinical practice.
Methods AS patients eligible for treatment with etanercept (50 mg subcutaneously (SC) every week) (n=174) or adalimumab (40 mg SC every 2 weeks) (n=81) were followed in a prospective observational cohort for 3 years. Prediction models were developed with linear mixed modelling using backward regression with 17 baseline variables. The Bath AS Functional Index (BASFI) questionnaire was used as outcome measure for function.
Results At baseline 255 patients were included (68% male), with a mean age of 44 (±11) years, active disease (Bath AS Disease Activity Index 5.8±1.9) and mean BASFI of 5.4±2.4. There is a progressive and significant improvement in physical functioning during the first 24 weeks after the start of TNFi treatment (BASFI 24 weeks 3.3±2.6), followed by a stable course over time (BASFI 3 years 3.6±2.5) (figure). Therefore, these two time periods were analysed separately: from baseline up to 24 weeks and from 24 weeks up to 3 years follow-up. Mean follow-up duration was 1 year. During the first period patients <40 years, with lower BASFI values, absence of co morbidity and physically active at baseline had a more favourable course of physical functioning. This can result in a (clinically significant) difference of 2 points on the BASFI after 24 weeks compared with patients having the opposite characteristics. After 24 weeks up to 3-years, patients who were <40 years, HLA-B27 positive and had lower BASFI, BASMI and CRP values at baseline performed better.
Conclusions This study shows that improvement of physical functioning in TNFi treated AS patients continues up to 24 weeks, which is longer than the 3 months commonly used to evaluate the efficacy of TNFi therapy. The 3 year course is more favourable in patients <40 years and less physical limitations (BASFI) at baseline. Awareness of factors predicting physical function in TNFi treated AS patients could influence treatment strategy and potentially creates possibilities to optimize treatment.
Disclosure of Interest None declared
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