Objective To evaluate active inflammatory lesions (AIL) and structural changes (SC) in patients with active non-radiographic axial spondyloarthritis (nr-axSpA) compared with patients with ankylosing spondylitis (AS) on whole-body MRI (wb-MRI). Method 75 patients with active disease and a symptom duration of <5 years (39 with AS and 36 with nr-axSpA) were investigated with a comprehensive wb-MRI protocol and scored for AIL and SC in the spine, sacroiliac joints (SIJs) and non-axial manifestations. Results 92% of patients with AS showed active inflammation in the SIJ, 53% in the spine and 94% and 39%, respectively, in the nr-axSpA group. There was a non-significant trend towards more inflammation in patients with AS compared with patients with nr-axSpA in SIJs and spine. Peripheral enthesitis/osteitis was more common in patients with AS (n=22) than in those with nr-axSpA (n=12) (p=0.05). SC were more common in patients with AS than in those with nr-axSpA, with significantly higher scores for SIJ fatty bone marrow deposition (FMD) in patients with AS (4.8±3.2) compared with those with nr-axSpA (2.4±2.7; p=0.001) and more frequent bone proliferation in the spine and the SIJ (p=0.02 and p=0.005, respectively). SIJ erosions were more common in AS (score 4.2±2.3) than in nr-axSpA (score 3.8±1.8) patients (not significant). Conclusions Wb-MRI detects active inflammation and SC more frequently in the SIJs than in the spine. Half of the patients showed inflammation in non-axial sites. Active inflammatory and structural lesions were present both in patients with AS and those with nr-axSpA, being only slightly more common in patients with AS.

Objective To assess the diagnostic accuracy of radiography (X-ray, XR), CT and MRI of the sacroiliac joints for diagnosis of axial spondyloarthritis (axSpA). Methods 163 patients (89 with axSpA; 74 with degenerative conditions) underwent XR, CT and MR. Three blinded experts categorised the imaging findings into axSpA, other diseases or normal in five separate reading rounds (XR, CT, MR, XR +MR, CT +MR). The clinical diagnosis served as reference standard. Sensitivity and specificity for axSpA and inter-rater reliability were compared. Results XR showed lower sensitivity (66.3%) than MR (82.0%) and CT (76.4%) and also an inferior specificity of 67.6% vs 86.5% (MR) and 97.3% (CT). XR +MR was similar to MR alone (sensitivity 77.5 %/specificity 87.8%) while CT+MR was superior (75.3 %/97.3%). CT had the best inter-rater reliability (kappa=0.875), followed by MR (0.665) and XR (0.517). XR +MR was similar (0.662) and CT+MR (0.732) superior to MR alone. Conclusions XR had inferior diagnostic accuracy and inter-rater reliability compared with cross-sectional imaging. MR alone was similar in diagnostic performance to XR+MR. CT had the best accuracy, strengthening the importance of structural lesions for the differential diagnosis in axSpA.

Objectives: Osteitis condensans ilii (OCI) has become an important differential diagnosis for axial spondyloarthritis (axSpA). The objective of this matched case–control study was to investigate demographic, clinical, laboratory and MRI characteristics of OCI as compared with axial spondyloarthritis (axSpA). Methods: A total of 60 patients diagnosed with OCI were included in the final analysis. From 27 of these patients, MRIs of the sacroiliac joints were available. OCI patients were matched with a 1:1 ratio by back pain duration to patients with definite axSpA in order to compare clinical, laboratory and MRI characteristics. Results: The OCI patients were nearly all females (96.7 vs 46.7%), had a significantly lower prevalence of inflammatory back pain (39.5 vs 88.9%), a significantly lower percentage of HLA-B27 positives (35.2 vs 80.0%) and a lower prevalence of the majority of other SpA features as compared with axSpA patients. Interestingly, there was no difference in the prevalence of osteitis in the sacroiliac joints (92.6 vs 85.2% in OCI and axSpA, respectively, P = 0.44), but there was a difference in the prevalence of erosions (7.4 vs 66.7%, respectively, P = 0.0001). In addition, in OCI nearly all lesions were localized in the anterior part of the sacroiliac joints while in axSpA lesions were localized predominantly in the middle part of the joint (for osteitis: 96 vs 4% in OCI and 28.6 vs 71.4% in axSpA; P = 0.0002 for the inter-group difference). Conclusion: Clinical and imaging features of OCI compared with axSpA are described that should help in differential diagnosis.

A deep learning tool was able to detect active inflammatory and structural changes indicative of axial spondyloarthritis at MRI of sacroiliac joints. Background MRI is frequently used for early diagnosis of axial spondyloarthritis (axSpA). However, evaluation is time-consuming and requires profound expertise because noninflammatory degenerative ...

In 2009, the Assessment of SpondyloArthritis international Society (ASAS) published a definition of ‘active sacroiliitis on magnetic resonance imaging (MRI) for classification of axial spondyloarthritis’. This new definition of an ‘ASAS-positive MRI’ was integral to new classification criteria for axial spondyloarthritis that were published in the same year. The ASAS MRI definition had the considerable advantage of simplicity and the definition gained popularity as guidance for interpreting MRI of the sacroiliac joints in clinical practice. However, classification criteria are not designed for use in clinical practice with the consequence that overreliance on the presence of bone marrow edema, which is the principal determinant of an ‘ASAS-positive MRI’, may result in a tendency to overcall inflammatory sacroiliitis in the clinical setting. This article aims to inform the reader about the rationale behind the ASAS definition of a positive MRI and ASAS classification criteria, their proper use in research and why they should not be used in clinical practice. The article also contains guidance for an updated imaging protocol and interpretation of images including typical imaging findings, differential diagnosis, and common pitfalls.