Background/Purpose: Validation of clinical measures of disease in non-radiographic axial SpA (nr-axSpA) has been limited, especially using inflammatory and structural lesions on MRI as gold standard. Ankylosing Spondylitis Disease Activity Score (ASDAS) has been proposed as an optimal outcome measure, but is less feasible than Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) due to the need to assess CRP. We assessed which clinical measures best reflect the spectrum of MRI lesions in the sacroiliac joints (SIJ) of patients with nr-axSpA, and the effect of treating with an anti-TNF agent. 

Methods: Patients had axial SpA per the Assessment of SpondyloArthritis (ASAS) classification criteria, but did not meet modified NY radiographic criteria. Patients had symptoms >3 months and <5 years, BASDAI ≥4, and failed ≥2 NSAIDs. Patients were randomized to etanercept (ETN) 50 mg/wk or placebo; after 12 wks, all patients received open-label ETN 50 mg/wk. Clinical endpoints were evaluated throughout the study; MRI of SIJ and spine was performed by 2 central readers at baseline (BL), wks 12 and 48, to assess bone marrow edema using the Spondyloarthritis Research Consortium of Canada (SPARCC) SIJ score. In a post-hoc analysis, structural lesions were scored using the SPARCC SIJ structural (SSS) method, assessing fat metaplasia, erosion, backfill, and ankylosis on T1-weighted spin echo (T1WSE) MRI. Two independent readers scored BL and 48 wk T1WSE MRI scans from 187 cases blinded to outcomes and short tau inversion recovery (STIR) MRI; readers’ mean scores were used. SPARCC score ≥2 for SIJ defined positive MRI evidence of inflammation. For the analysis, patients were pooled, and wk 48 change was analyzed using Spearman correlations, adjusted for treatment.

Results: Mean (SD) age was 32 (7.8) years, 60.5% were male, mean (SD) duration of symptoms was 2.5 (1.8) years. A total of 73% of patients were human leukocyte antigen B27 (HLA-B27) positive; 81% met the ASAS MRI imaging criteria at BL. A significant decrease in clinical (ASDAS, BASDAI, CRP) and MRI (SPARCC SIJ inflammation, SSS erosion) measures of active disease was noted by wk 48. There were no significant correlations at BL between BASDAI and any MRI lesion scores. There was significant BL correlation between SPARCC SIJ inflammation score and ASDAS (r=0.19, p=0.005) and CRP (r=0.22, p=0.002). Over 48 wks, there was significant correlation between change in ASDAS and changes in SPARCC SIJ inflammation (r=0.40, p<0.0001), SSS erosion (r=0.25, p=0.0007), and SSS backfill (r=-0.23, p=0.002). Change in CRP correlated significantly with changes in SPARCC SIJ inflammation (r=0.35, p<0.0001) and SSS erosion (r=0.18, p=0.02). Change in BASDAI correlated significantly with changes in SPARCC SIJ inflammation (r=0.25, p=0.0008), SSS backfill (r=-0.18, p=0.02), and SSS erosion (r=0.16, p=0.03). Correlations between ASDAS and MRI measures of sacroiliitis were strongest in the ETN group through 48 wks.

Conclusion: ASDAS is the preferred clinical measure of disease activity in nr-axSpA. Of all MRI assessments, change in SPARCC SIJ inflammation seems most closely aligned with changes in ASDAS, CRP and BASDAI, though the correlations are modest.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-ankylosing-spondylitis-disease-activity-score-more-closely-reflects-mri-parameters-of-sacroiliitis-than-the-bath-ankylosing-spondylitis-disease-activity-index-in-patients-with-non-radiographic-axi/