Background Ankylosing spondylitis (AS) is characterized by inflammation in the spine. The relationship between MRI inflammation and measures of clinical disease activity is incompletely understood.
Objectives To investigate the relationship of MRI inflammation to measures of clinical disease activity and to different treatment responses in patients with AS who were treated with a TNF inhibitor.
Methods A random 80% sample of the ASSERT database was used for this analysis. ASSERT was a 24-week (wk) RCT comparing infliximab and placebo in patients with active AS, with an open extension until 102wk. MRIs at baseline, wk24 and wk102 were scored by 2 independent readers using the ASspiMRI-activity score. For this analysis, scores were re-coded using the Berlin modification in order to exclude erosions from the scores. Analyses were performed on average scores of the two readers for all patients at baseline, for changes in the infliximab group at 24wk and for changes in all patients at 102wk. Spearman correlation coefficients were determined. Treatment responses according to the ASDAS, BASDAI and ASAS20 were calculated at 24 and 102wk. For each treatment response criterion, subgroups of responders and non-responders changes in MRIa scores were compared using 3 statistical approaches: 1) the standardized mean difference (SMD), 2) the F-score and p-value of a two-sided ANOVA on van der Waerden normal scores, 3) the difference in the standardized response mean (ΔSRM).
Results At baseline, ASDAS (r=0.16) and CRP (r=0.28) correlated significantly with MRIa scores. Similarly, changes in ASDAS (r=0.22 at 24wk, r=0.23 at 102wk) and changes in CRP (r=0.25 at 24wk, r=0.32 at 102wk) correlated significantly with changes in MRIa scores. Higher baseline ASDAS and CRP values were associated with greater decreases in MRIa scores (ASDAS: r=-0.14 at 24wk, r=-0.15 at 102wk; CRP: r=-0.25 at 24wk, r=-0.31 at 102wk). None of the associations described for CRP and ASDAS were present for BASDAI, individual BASDAI questions and patient global. Differences in MRIa change scores between responders and non-responders were greater when subgroups were defined according to the ASDAS response criterion than when subgroups were defined according to the BASDAI or ASAS20 response criteria (table: changes from baseline to wk102 in MRIa scores, n=179).
Conclusions MRIa correlates better with CRP than with other measures of disease activity. By including both CRP and patient reported outcomes in its formula, ASDAS has the advantage of providing combined information on objective and subjective measures. As a response measure ASDAS also better reflects the spinal inflammatory disease process in AS than the other frequently used response measures.
Disclosure of Interest None Declared
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