AB0658 Influence of Known Risk Factors on Spinal Radiographic Progression in Ankylosing Spondylitis Patients Receiving Long-Term Treatment with TNF Inhibitors: Results from The Glas Cohort

BackgroundIn ankylosing spondylitis (AS), the most important prognostic factor for spinal radiographic progression is the presence of syndesmophytes at study entry. In addition, male gender, older age, longer symptom duration, smoking, HLA-B27 positivity, and increased inflammatory markers were found to be associated with radiographic progression in AS.1ObjectivesTo investigate the influence of known risk factors on spinal radiographic progression in AS patients receiving long-term treatment with TNF inhibitors.MethodsConsecutive patients from the GLAS cohort receiving TNF inhibitors with baseline and biannual spinal radiographs untill 6 years of follow-up were included. Radiographs were scored in chronological time order by two independent readers according to the mSASSS. Single linear imputation of radiographic data was used in case patients had missing data at one or more intermediate follow-up visits. The influence of the earlier mentioned risk factors for radiographic progression was investigated using univariable and multivariable generalized estimating equations (GEE). Subsequently, radiographic progression was modeled with different time functions (linear and non-linear) to provide the best fit for the data in patients with and without risk factors. A time function with p≤0.05 contributed significantly to the model and the estimated mean progression rates of the 2-year time intervals were calculated.ResultsEighty patients were included; 70% were male, 78% HLA-B27+, mean age was 41±10 years, median symptom duration 14 (IQR: 8–24) years, mean BASDAI 6.0±1.7, mean ASDAS 3.8±0.8, and mean mSASSS 8.7±13.3.During 6 years of follow-up, mean progression was 4.2±4.8 mSASSS units. GEE revealed that baseline syndesmophytes, gender, age, and symptom duration were significantly associated with radiographic damage over time. No significant associations were found for smoking, HLA-B27 status, and elevated CRP levels. The presence of baseline syndesmophytes was the only independent predictor for progression.Baseline mSASSS was highest in AS patients with baseline syndesmophytes, male gender, age ≥40 years, and symptom duration ≥10 years. In these patients, mSASSS progression followed a non-linear course showing a reduction in estimated progression rates over time (Table 1). Most patients with syndesmophytes also had one or more other risk factors (e.g. male gender and symptom duration ≥10 years). A linear course with low estimated progression rates was found in pa