MRI-assessed structural damage progression in sacroiliac joints of European routine care patients with axial spondyloarthritis receiving biological or conventional therapy

Objectives To describe progression of magnetic resonance imaging (MRI)–detected sacroiliac joint (SIJ) structural lesions in patients with axial spondyloarthritis (axSpA) in routine care. Methods Bionaïve patients with axSpA from 5 European countries were included if a follow-up SIJ MRI was available 1 to 4 years after baseline. MRIs were centrally assessed using the Spondyloarthritis Research Consortium of Canada SIJ scoring systems by readers blinded to chronology. Patients were stratified by initiation of biological therapy during follow-up. Structural progression was described and compared. Results Of 179 patients, 122 had a first MRI indicative of SpA. In these patients, baseline scores for bone marrow oedema (BME), fat lesions, and erosions were significantly higher in those initiating biologic disease-modifying antirheumatic drugs (bDMARDs) (n = 53) than in conventionally treated patients (n = 59). The MRI interval was 1.8 years in bDMARD-treated patients and 2.3 years in conventionally treated patients. In bDMARD-treated patients, mean Spondyloarthritis Research Consortium of Canada changes during MRI follow-up were BME −14.7, fat lesions +1.2, erosions −2.4, backfill +1.6, and ankylosis +0.2. Corresponding changes in conventionally treated patients were −3.0, +0.03, −0.04, +0.9, and +0.7. Ankylosis progression occurred in 15% of conventionally treated patients and 9% of those receiving bDMARDs. Backfill and ankylosis at baseline correlated with ankylosis progression in conventionally treated patients (Spearman's ρ = 0.38 and 0.42) but not in bDMARD-treated patients (ρ = −0.17 and 0.09). Conclusions Erosions decreased only with bDMARD therapy. Baseline backfill was associated with ankylosis progression in conventional but not bDMARD-treated patients, suggesting a potential dissociation between backfill and ankylosis under biologics. Future studies should assess causality.