Spondyloarthritis & psoriatic arthritis
Which definitions for MRI sacroiliac joint lesions predict the diagnosis of early axial spondyloarthritis best? A 2-year follow-up in the SPACE cohort
An erratum to this article was published (RMD Open, 18 May 2026 ↗)
Authors' conclusion
The ASAS-MRI-SIJ+ definition outperforms the MRI study group AL. The Leiden SL combined with the ASAS-MRI-SIJ+ definition is validated, most sensitive and feasible as it simultaneously upholds lesion quantification and detection precision, making it the preferred approach.
Study context
- Population
- Patients with chronic back pain (≤2 years) from the SPACE cohort, diagnosed as axial spondyloarthritis (axSpA) or non-axSpA after 2 years follow-up52% axSpA
- Participants
- 643 patients
- Comparison
- Proposed Leiden and ASAS-MRI study group structural (SL) and AL MRI of the sacroiliac joints (MRI-SIJ) definitions vs the current ASAS-MRI-SIJ+ definition
- Outcome
- Predictive validity of MRI-SIJ definitions for axSpA diagnosis; validation required specificity and PPV ≥95%
- Follow-up
- 2 years
Methodological detailsprospective cohort (SPACE), 2-year follow-up, three central readers
- Prospective cohort (SPACE)
- 2-year follow-up
- Three central readers
Performance
As reported in the abstract
Diagnostic performance of AL definitions for axSpA
| Test or model | Sensitivity | Specificity |
|---|---|---|
| ASAS-MRI-SIJ+ | 40% | 98% |
| MRI study group AL | 31% | 99% |
| Leiden SL + ASAS-MRI-SIJ+ | 46% | — not stated in the abstract |
Sensitivity
ASAS-MRI-SIJ+40%
MRI study group AL31%
Leiden SL + ASAS-MRI-SIJ+46%
Specificity
ASAS-MRI-SIJ+98%
MRI study group AL99%
Leiden SL + ASAS-MRI-SIJ+— not stated in the abstract
— not stated in the abstract
- Leiden SL with ASAS-MRI-SIJ+ met the validation threshold with the highest sensitivity
- 46%
Further findings
SL definitions · 2 years
- SL frequency (infrequent)
- 2%-14%
- Increase in sensitivity by SL beyond AL alone
- 6%-11%
- All Leiden and most MRI study group SL definitions met the validation threshold, except 'erosion in ≥2 consecutive slices' and the overall MRI study group definition (PPV <95%)
Original publication
Which definitions for MRI sacroiliac joint lesions predict the diagnosis of early axial spondyloarthritis best? A 2-year follow-up in the SPACE cohort. RMD Open. Published 9 March 2026. doi:10.
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