ABS0977 PERFORMANCE OF THE ASAS PRELIMINARY DATA-DRIVEN MRI LESION CUT-OFFS FOR A POSITIVE MRI OF THE SACROILIAC JOINTS IN PATIENTS WITH AXIAL SPONDYLOARTHRITIS WITH AND WITHOUT PSORIASIS, IRITIS, AND COLITIS

Background:
ASAS has proposed preliminary cut-offs for a positive MRI of the sacroiliac joints (SIJ) inflammatory and structural lesion in patients with axial spondyloarthritis (axSpA), which should be more stringent and aimed for higher specificity. The ASAS derived cut-offs are based on numbers of SIJ with the affected lesion, being ≥3 for erosion (ER), ≥4 for bone marrow edema (BME), ≥5 for fat lesion (FAT), and ≥2 for deep fat lesion extending ≥1cm from subchondral bone.
Objectives:
The aim was to validate these cut-offs in axSpA patients with different clinical phenotypes i.e., patients with or without concomitant psoriasis (PsO), acute anterior uveitis (AAU), and inflammatory bowel disease (IBD), and age- and gender-matched patients with non-specific back pain (NSBP).
Methods:
AxSpA patients fulfilling the modified New York criteria (mNY) were included from a prospective, observational cohort. All axSpA cases with AAU(n=45) PsO(n=44), or IBD(n=27), diagnosed by an ophthalmologist, dermatologist, or gastroenterologist, or axSpA without extra-articular features(n=45), and with available MRI SIJ scans were matched for age and gender with scans from NSBP controls(n=78). Three readers blinded to clinical information evaluated the MRI scans according to the ASAS MRImagine-consensus. This included global assessment and detailed scoring of lesions per SIJ quadrant or halves according to the SPARCC method. Cut-offs for backfill (BF), and ankylosis (ANK) were assessed according to number of SIJ halves. Sensitivity and specificity of MRI cut-offs from≥2 to≥5 SIJ quadrants (for BME, ER, FAT, SCL) or halves (BF, ANK) with diagnosis of axSpA as gold standard, were analyzed.
Results:
For BME, a substantial increase in specificity was evident with a cut-off≥4 at 92.3% with limited impact on sensitivity for diagnosis of axSpA among all subgroups when compared to a cut-off≥3 (Table 1). For ER, specificity was 96.2% at a cut-off≥3 with limited impact on sensitivity when compared to a cut-off 2. For FAT, specificity was 94.9% at a cut-off≥5 with limited impact on sensitivity when compared to a cut-off≥4, while a deep fat lesion already had high specificity of 96.2% even at a cut-off≥2. BF and ANK had 100% specificity at cut-offs of≥2 while SCL had high specificity, but sensitivity was low even at the cut-off≥2.
Conclusion:
The data-driven MRI lesion cut-offs demonstrated high performance characteristics, supporting the validity of the preliminary ASAS Data-Driven MRI lesion cut-offs.