Background/Purpose: In two years, approximately 10% of patients with non-radiographic axial spondyloarthritis (nr-axSpA) progresses to ankylosing spondylitis (AS). There are no data available of more long-term follow-up. The objective of this study was to assess the rate of progression of nr-axSpA to AS in patients with up to six years of follow-up.

Methods: Patients enrolled in the ongoing Groningen Leeuwarden Axial Spondyloarthritis (GLAS) cohort, classified as nr-axSpA at baseline with a baseline pelvic radiograph and at least one two-year follow-up radiograph, were selected for our analyses. These baseline, two-, four- and six-year radiographs were randomized with radiographs of AS patients in a three-to-one ratio and scored with known time sequence according to the modified New York (mNY) criteria by two trained readers (SK and RW). In case of discrepancy in classification, the score of a third independent reader (AS) was used. Progression to AS was defined as progression in mNY sacroiliitis score to ≥2 bilaterally or ≥3 unilaterally.

Results: 79 patients were clinically classified as nr-axSpA at baseline confirmed by radiographic score. At baseline, mean age was 39 ± 10 years, 48% was male, median symptom duration was 6 (IQR 3-17) years, mean ASDAS was 2.8 ± 1.1, and 71% was HLA-B27+. After two, four and six years, 8/79 (10.1%), 4/48 (8.3%) and 3/24 (12.5%) nr-axSpA patients progressed to AS. In total, 23 and 20 patients did not yet reach follow at four and six years, respectively (Table 1).

Conclusion: In our observational cohort of patients with axial spondyloarthritis with up to six years of follow-up, every two years approximately 10% of patients progressed from nr-axSpA to AS. The next step will be to evaluate associations with patient and disease characteristics.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/radiographic-sacroiliitis-progression-up-to-six-years-of-follow-up-in-patients-with-non-radiographic-axial-apondyloarthritis/