Background It is known that in axial spondyloarthritis (axSpA) inflammatory lesions on MRI of the SI joints (MRI-SI) can change over time. The usefulness of repeating imaging in the diagnostic process is unclear.
Objectives To investigate how patients with short-term chronic back pain are classified by the ASAS axSpA- criteria at baseline and after 1-year follow-up, focussing on the role of imaging.
Methods Patients in the SPACE-cohort (back pain: ≥3 months, ≤2 years, onset <45 years) with (suspicion of) axSpA underwent MRI and X-rays of the SI-joints at baseline and 1-year follow-up. Patients with complete MRI- and X-SI data at both timepoints were included in the analysis (n=185). MRI-SI and X-SI were scored by 3 different well-calibrated readers independently according to the ASAS-definition for a positive MRI and the mNY-criteria, blinded for patient characteristics and time sequence. Fulfillment of ASAS-MRI or mNY-criteria was considered positive if 2/3 readers agreed. At each timepoint, patients were classified according the ASAS axSpA-criteria and grouped in the different arms (imaging arm: mNY+/- or MRI+/-; clinical arm, fulfilment of both arms and possible axSpA). At year one, in contrary to the normal application of the criteria, where a positive feature remains positive:we grouped patients according to the finding at that timepoint, ignoring previous imaging findings.
Results At baseline, 92/185 patients (49.7%) fulfilled the ASAS criteria (clinical arm: 53; imaging arm: 15, both arms: 24) (table). At 1 year, 14 additional patients fulfilled the criteria (8 clinical arm; 5 imaging arm only; 1 both arms). After 1 year, in 12 patients MRI-SI became positive. As a result, 14/93 (15.1%) of the no SpA or possible SpA patients at baseline could be classified additionally as axSpA because of additional SpA features (n=8), a positive MRI (n=4) or sacroiliitis according to the mNY-criteria (n=2), On the other hand, MRI-SI became negative after 1 year in 12 other patients. Of these patients, 10 still fulfilled the ASAS criteria (clinical arm (n=7) or both arms (n=3)). Only 4 patients (classified as axSpA at baseline) would be missed if imaging would have been performed only at 1 year (due to negative MRI or x-ray findings).
Conclusions In our cohort, a signifcant number of patients with no SpA or possible SpA at baseline developed (additional) SpA features leading to fulfilment of axSpA criteria at year one. However, our data show the robustness of the axSpA criteria and there is only limited evidence for repeating imaging after one year.
Disclosure of Interest None declared
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