Background Since 2012, a cut-off value of ≥3 inflammatory lesions was suggested by the ASAS/OMERACT group, as positive MRI of the spine (MRI-spine). Moreover, fatty lesions on MRI-spine are associated with axial Spondyloarthritis (axSpA).
Objectives To determine the prevalence of inflammatory (BME) and fatty lesions on MRI of the spine in patients (pts) with and without axSpA
Methods Pts aged 18-50 with inflammatory back pain (≥3 months, ≤3 years) from 25 participating centers in France were included in the DESIR-cohort (n=708). All available baseline MRIs were independently scored by 2 well-calibrated readers, blinded to any other data. In case of disagreement, an experienced radiologist served as adjudicator. BME and fatty lesions typical for axSpA were scored when visible on ≥2 consecutive slices. Prevalence of MRI lesions was calculated based on several cut-offs and lesions were considered present if 2/3 readers agreed
Results All pts with symptom onset <45 yrs with MRI-spine (n=549) were included in the analyses. Pts fulfilling the ASAS criteria could either fulfill both arms, only the imaging arm or only the clinical arm. The first 2 groups were subdivided; pts with radiographic sacroiliitis (mNY+) & sacroiliitis on MRI (MRI+), pts with mNY+ & no sacroiliitis on MRI (MRI-), pts without radiographic sacroiliitis (mNY-) & MRI+. BME lesions occur in all different subgroups of the ASAS criteria and in pts without axSpA (table). The prevalence in no SpA group (which can be seen as false positives) is only 6.1%. With a cut-off ≥2 BME lesions false positives drop below 5% while the prevalence in the ASAS axSpA groups is still reasonable. Especially prevalence in pts with mNY+ & MRI+ is very high; 61.9% (both arms positive) and 43.8% (imaging arm only positive). Fatty lesions are seen slightly less often seen in all patient groups. However the same trend is seen as with BME lesions; Even with cut-off ≥1 the prevalence in no SpA group is low (5.5%), with cut-off ≥2 false positives drop below 5% and again pts with mNY+ & MRI+ have the highest percentage of spinal fatty lesions
Conclusions In a low percentage of pts without axSpA BME and fatty lesions is found indicating that spinal BME and fatty lesions are specific for patients with axSpA. These lesions are especially prevalent in pts with sacroiliitis on imaging. In this cohort, a cut-off ≥2 or ≥3 BME lesions and similarly ≥2 or ≥3 fatty lesions discriminate best between pts with and without axSpA
Disclosure of Interest None declared