Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose: Inflammation on MRI of the sacroiliac joints (SIJ) in patients with spondyloarthritis (SpA) is a major criterion in the Assessment of SpondyloArthritis (ASAS) classification criteria for axial SpA, which are based on expert clinical opinion as gold standard. The definition of a positive SIJ MRI in the ASAS criteria was generated by consensus among experts. Studies using a data-driven approach are scarce. We aimed to assess candidate definitions for a positive SIJ MRI using both clinical gold standard and confidence in the diagnosis of SpA according to global assessment of MRI (T1-weighted and STIR sequences) by expert readers.
Methods: The study population comprised 2 independent cohorts (cohort A/B) of 157 consecutive patients with back pain ≤50 years newly referred to 2 university clinics, and 20 healthy controls. Patients were classified according to clinical examination and pelvic radiography as having non-radiographic SpA (n=51), ankylosing spondylitis (n=34), or mechanical back pain (n=72). SIJ MRI were assessed by 4 blinded readers according to a standardized module. Readers recorded their level of confidence in the diagnosis of SpA by global evaluation of the MRI scan on a 0-10 scale (0 = definitely not SpA; 10 = definite SpA). An MRI-based gold-standard criterion for SpA was pre-specified as the majority of readers (≥3/4) recording a confidence of 8-10. We estimated the type and extent of involvement according to number of affected SIJ quadrants attaining specificity of ≥90% for SpA using ROC analysis according to both clinical and MRI-based gold-standard criteria.
Results: The agreement between 4 readers regarding confidence for MRI-based global assessment of SpA was substantial with kappa of 0.76/0.80 for cohort A/B. BME was recorded in up to 30.0%/24.2% of controls in cohort A/B, whereas erosion was seen in only 0%/12.1% of controls. The combination of erosion and/or BME increased sensitivity compared to either lesion alone without reducing specificity irrespective of which gold standard criterion was used.
Sensitivity and cut-off for number of affected SIJ quadrants for a pre-defined specificity ≥0.90, and AUC, for the 2 gold standards and for cohort A/B
| Gold standard | Lesion | Sensitivity | Number of SIJ quadrants | AUC |
| MRI criterion | BME | 0.91/0.83 | 3/2 | 0.97/0.91 |
| Clinical evaluation | BME | 0.73/0.48 | 4/4 | 0.91/0.75 |
| MRI criterion | ER | 1.00/1.00 | 1/1 | 1.00/1.00 |
| Clinical evaluation | ER | 0.83/0.58 | 1/2 | 0.94/0.79 |
| MRI criterion | BME+ER | 1.00/1.00 | 3/2 | 1.00/1.00 |
| Clinical evaluation | BME+ER | 0.83/0.58 | 4/6 | 0.96/0.83 |
AUC: Area under the curve. BME: Bone marrow edema. ER: Erosion. Number of SIJ quadrants: Cut-off for the number of affected SIJ quadrants
Conclusion: This data driven study shows that assessment of the T1-weighted sequence enhances diagnostic certainty when viewed simultaneously with the STIR and supports the case for revision of the ASAS definition of a positive MRI in SpA.
Disclosure:
U. Weber,
None;
V. Zubler,
None;
S. J. Pedersen,
None;
K. Rufibach,
None;
R. G. Lambert,
None;
S. Chan,
None;
M. Ostergaard,
None;
W. P. Maksymowych,
None.
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