Background For years, it was unclear if inflammation and radiographic progression were related in AS, but studies were only of short follow-up and not analysed optimally.
Objectives To analyse the long-term relationship between disease activity and radiographic damage.
Methods Patients from the Outcome in AS International Study (OASIS) were followed-up for 12 years, with biannual clinical and radiographic assessments. Two readers independently scored the x-rays according to the mSASSS. The relationship between disease activity measures (BASDAI, ASDAS-CRP, CRP, patient's global assessment and spinal pain) and radiographic damage was investigated using generalized estimating equations. Auto-regressive models with 2-year time-lags were used and analyses were adjusted for potential confounders. Different models were constructed: model 1- ASDAS (continuous); model 2– ASDAS disease activity states; model 3– BASDAI continuous and CRP; model 4– BASDAI categories and CRP; model 5– patient global and CRP; model 6– spinal pain and CRP. Model fit was compared using the quasi-likelihood information criterion (QIC).
Results A total of 184 patients were included (70% males, mean (SD) age: 43 (12) years, mean symptom duration: 20 (12) years and 83% HLA-B27 positive). All disease activity measures were significantly longitudinally associated with radiographic progression. Neither medication, nor the presence of extra-articular manifestations confounded this relationship. The models with ASDAS had the best fit (i.e. lowest QIC): An increase in one ASDAS-unit led to an increase in 0.72 mSASSS-units and a “very high disease activity state” (i.e. ASDAS>3.5) compared to inactive disease (i.e. ASDAS<1.3) represented an additional progression of 2.31 mSASSS-units per 2 years (Table). Results were consistent across disease activity measures. The effect of ASDAS on mSASSS was higher in males vs females (β 0.98 vs -0.06) and in patients with shorter vs longer (<18 vs ≥18 years) disease duration (0.84 vs 0.16).
Conclusions In AS disease activity is unequivocally longitudinally associated with radiographic progression. ASDAS is the best measure to reflect this relationship. The effect of disease activity on radiographic damage is more pronounced in men and in the earlier phases of the disease.
Disclosure of Interest : None declared
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