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Objectives To determine patterns of variation of subchondral T2 signal changes in pediatric sacroiliac joints (SIJ) by location, age, sex, and sacral apophyseal closure. Methods MRI of 502 SIJ in 251 children (132 girls), mean age 12.4 years (range 6.1–18.0), was obtained with parental informed consent. One hundred twenty-seven out of 251 had asymptomatic joints and were imaged for non-rheumatologic reasons, and 124 had low back pain but no sign of sacroiliitis on initial clinical MRI review. After calibration, three subspecialist radiologists independently scored subchondral signal changes on fat-suppressed fluid-sensitive sequences from 0 to 3 in 4 locations, and graded the degree of closure of sacral segmental apophyses. Associations between patient age, sex, signal changes, and apophyseal closure were analyzed. Results Rim-like subchondral increased T2 signal or “flaring” was much more common at sacral than iliac SIJ margins (72% vs 16%, p  < 0.001) and was symmetrical in > 90% of children. Iliac flaring scores were always lower than sacral, except for 1 child. Signal changes decreased as sacral apophyses closed, and were seen in < 20% of subjects with fully closed apophyses. Signal changes were more frequent in boys, and peaked in intensity later than for girls (ages 8–12 vs. 7–10). Subchondral signal in iliac crests was high throughout childhood and did not correlate with other locations. Conclusions Subchondral T2 “flaring” is common at SIJ of prepubertal children and is generally sacral-predominant and symmetrical. Flaring that is asymmetrical, greater in ilium than sacrum, or intense in a teenager with closed apophyses, is unusual for normal children and raises concern for pathologic bone marrow edema. Key Points • A rim of subchondral high T2 signal is commonly observed on MRI at pediatric sacroiliac joints, primarily on the sacral side before segmental apophyseal closure, and should not be confused with pathology. • Unlike subchondral signal changes elsewhere, high T2 signal underlying the iliac crest apophyses is a near-universal normal finding in children that usually persists throughout adolescence. • The following patterns are unusual in normal children and are suspicious for pathology: definite iliac flaring, iliac flaring more intense than sacral flaring, left-right difference in flaring, definite flaring of any pattern in teenagers after sacral apophyseal closure.

ObjectivesTo review and update the existing definition of a positive MRI for classification of axial spondyloarthritis (SpA).MethodsThe Assessment in SpondyloArthritis International Society (ASAS) MRI working group conducted a consensus exercise to review the definition of a positive MRI for inclusion in the ASAS classification criteria of axial SpA. Existing definitions and new data relevant to the MRI diagnosis and classification of sacroiliitis and spondylitis in axial SpA, published since the ASAS definition first appeared in print in 2009, were reviewed and discussed. The precise wording of the existing definition was examined in detail and the data and a draft proposal were presented to and voted on by the ASAS membership.ResultsThe clear presence of bone marrow oedema on MRI in subchondral bone is still considered to be the defining observation that determines the presence of active sacroiliitis. Structural damage lesions seen on MRI may contribute to a decision by the observer that inflammatory lesions are genuinely due to SpA but are not required to meet the definition. The existing definition was clarified adding guidelines and images to assist in the application of the definition.ConclusionThe definition of a positive MRI for classification of axial SpA should continue to primarily depend on the imaging features of ‘active sacroiliitis’ until more data are available regarding MRI features of structural damage in the sacroiliac joint and MRI features in the spine and their utility when used for classification purposes.

ObjectivesThe Assessment of SpondyloArthritis international Society (ASAS) MRI working group (WG) was convened to generate a consensus update on standardised definitions for MRI lesions in the sacroiliac joint (SIJ) of patients with spondyloarthritis (SpA), and to conduct preliminary validation.MethodsThe literature pertaining to these MRI lesion definitions was discussed at three meetings of the group. 25 investigators (20 rheumatologists, 5 radiologists) determined which definitions should be retained or required revision, and which required a new definition. Lesion definitions were assessed in a multi-reader validation exercise using 278 MRI scans from the ASAS classification cohort by global assessment (lesion present/absent) and detailed scoring (inflammation and structural). Reliability of detection of lesions was analysed using kappa statistics and the intraclass correlation coefficient (ICC).ResultsNo revisions were made to the current ASAS definition of a positive SIJ MRI or definitions for subchondral inflammation and sclerosis. The following definitions were revised: capsulitis, enthesitis, fat lesion and erosion. New definitions were developed for joint space enhancement, joint space fluid, fat metaplasia in an erosion cavity, ankylosis and bone bud. The most frequently detected structural lesion, erosion, was detected almost as reliably as subchondral inflammation (κappa/ICC:0.61/0.54 and 0.60/0.83) . Fat metaplasia in an erosion cavity and ankylosis were also reliably detected despite their low frequency (κappa/ICC:0.50/0.37 and 0.58/0.97).ConclusionThe ASAS-MRI WG concluded that several definitions required revision and some new definitions were necessary. Multi-reader validation demonstrated substantial reliability for the most frequently detected lesions and comparable reliability between active and structural lesions.

ObjectivesTo compare the prevalence, clinical and radiographic characteristics of psoriatic spondyloarthritis (PsSpA) in psoriatic arthritis (PsA), with ankylosing spondylitis (AS).MethodsA prospective single-centre cross-sectional observational study recruited consecutive PsA and AS cases. Participants completed outcome measures, and underwent clinical examination, axial radiographic scoring and HLA-sequencing. Multivariable analyses are presented.ResultsThe 402 enrolled cases (201 PsA, 201 AS; fulfilling classification criteria for respective conditions) were reclassified based upon radiographic axial disease and psoriasis, as: 118 PsSpA, 127 peripheral-only PsA (pPsA), and 157 AS without psoriasis (AS) cases. A significant proportion of patients with radiographic axial disease had PsSpA (118/275; 42.91%), and often had symptomatically silent axial disease (30/118; 25.42%). Modified New York criteria for AS were fulfilled by 48/201 (23.88%) PsA cases, and Classification of Psoriatic Arthritis criteria by 49/201 (24.38%) AS cases. pPsA compared with PsSpA cases had a lower frequency of HLA-B*27 (OR 0.12; 95% CI 0.05 to 0.25). Disease activity, metrology and disability were comparable in PsSpA and AS. A significant proportion of PsSpA cases had spondylitis without sacroiliitis (39/118; 33.05%); they less frequently carried HLA-B*27 (OR 0.11; 95% CI 0.04 to 0.33). Sacroiliac joint complete ankylosis (adjusted OR, ORadj 2.96; 95% CI 1.42 to 6.15) and bridging syndesmophytes (ORadj 2.78; 95% CI 1.49 to 5.18) were more likely in AS than PsSpA. Radiographic axial disease was more severe in AS than PsSpA (Psoriatic Arthritis Spondylitis Radiology Index Score: adjusted incidence risk ratio 1.13; 95% CI 1.09 to 1.19).ConclusionsIn a combined cohort of patients with either PsA or AS from a single centre, 24% fulfilled classification criteria for both conditions. The pattern of axial disease was influenced significantly by the presence of skin psoriasis and HLA-B*27.

ObjectivesBone marrow oedema (BMO) on MRI of sacroiliac joints (SIJs) represents a hallmark of axial spondyloarthritis (SpA), yet such lesions may also occur under augmented mechanical stress in healthy subjects. We therefore sought to delineate the relationship between pregnancy/delivery and pelvic stress through a prospective study with repeated MRI. Results were matched with maternal, child and birth characteristics.MethodsThirty-five women underwent a baseline MRI-SIJ within the first 10 days after giving birth. MRI was repeated after 6 months and, if positive for sacroiliitis according to the Assessment of SpondyloArthritis International Society (ASAS) definition, after 12 months. BMO and structural lesions were scored by three trained readers using the Spondyloarthritis Research Consortium of Canada (SPARCC) method.ResultsSeventy-seven per cent of the subjects (27/35) displayed sacroiliac BMO immediately postpartum, 60% fulfilled the ASAS definition of a positive MRI. After 6 months, 46% of the subjects (15/33) still showed BMO, representing 15% (5/33) with a positive MRI. After 12 months, MRI was still positive in 12% of the subjects (4/33). Few structural lesions were detected. Intriguingly, in this study, the presence of BMO was related to a shorter duration of labour and lack of epidural anaesthesia.ConclusionA surprisingly high prevalence of sacroiliac BMO occurs in women immediately postpartum. Our data reveal a need for a waiting period of at least 6 months to perform an MRI-SIJ in postpartum women with back pain. This study also underscores the importance of interpreting MRI-SIJ findings in the appropriate clinical context.

Ankylosing spondylitis (AS) is the historic term used for decades for the HLA-B27-associated inflammatory disease affecting mainly the sacroiliac joints (SIJ) and spine. Classification criteria for AS have radiographic sacroiliitis as a dominant characteristic. However, with the availability of MRI of SIJ, it could be demonstrated that the disease starts long before definite SIJ changes become visible on radiographs. The Assessment of SpondyloArthritis international Society, representing a worldwide group of experts reached consensus on changes in the nomenclature pertaining to axial spondyloarthritis (axSpA), such as the terminology of diagnosis and of assessment of disease activity tools. These are important changes in the field, as experts in axSpA are now in agreement that the term axSpA is the overall term for the disease. A further differentiation, of which radiographic versus non-radiographic is only one aspect, may be relevant for research purposes. Another important decision was that the terms AS and radiographic axSpA (r-axSpA) can be used interchangeably, but that the preferred term is r-axSpA. Based on the decision that axSpA is the correct terminology, a proposal was made to officially change the meaning of the ASDAS acronym to ‘Axial Spondyloarthritis Disease Activity Score’. In addition, for simplification it was proposed that the term ASDAS (instead of ASDAS-CRP) should be preferred and applied to the ASDAS calculated with C reactive protein (CRP). It is hoped that these changes will be used consequently for education, in textbooks, manuscripts and presentations.

ObjectiveTo estimate sacroiliac joint radiographic (X-SIJ) progression in patients with axial spondyloarthritis (axSpA) and to evaluate the effects of inflammation on MRI (MRI-SIJ) on X-SIJ progression.MethodsX-SIJ and MRI-SIJ at baseline and after 2 and 5 years in patients with recent onset axSpA from the DESIR cohort were scored by three central readers. Progression was defined as (1) the shift from non-radiographic (nr) to radiographic (r) sacroiliitis (by modified New York (mNY) criteria) or alternative criteria, (2) a change of at least one grade or (3) a change of at least one grade but ignoring a change from grade 0 to 1. The effects of baseline inflammation on MRI-SIJ on 5-year X-SIJ damage (mNY) were tested by generalised estimating equations.ResultsIn 416 patients with pairs of baseline and 5-year X-SIJ present, net progression occurred in 5.1% (1), 13.0% (2) and 10.3% (3) respectively, regarding a shift from nr-axSpA to r-axSpA (1), a change of at least one grade (2) or a change of at least one grade but ignoring a change from grade 0 to 1 (3). Baseline MRI-SIJ predicted structural damage after 5 years in human leukocyte antigen-B27 (HLA-B27) positive (OR 5.39 (95% CI 3.25 to 8.94)) and in HLA-B27 negative (OR 2.16 (95% CI 1.04 to 4.51)) patients.ConclusionsFive-year progression of X-SIJ damage in patients with recent onset axSpA is limited but present beyond measurement error. Baseline MRI-SIJ inflammation drives 5-year radiographic changes.

BackgroundPatients with spondyloarthritis with radiographic sacroiliitis are traditionally classified according to the modified New York (mNY) criteria as ankylosing spondylitis (AS) and more recently according to the Assessment of SpondyloArthritis international Society (ASAS) criteria as radiographic axial spondyloarthritis (r-axSpA).ObjectiveTo investigate the agreement between the mNY criteria for AS and the ASAS criteria for r-axSpA and reasons for disagreement.MethodsPatients with back pain ≥3 months diagnosed as axSpA with radiographic sacroiliitis (mNY radiographic criterion) were selected from eight cohorts (ASAS, Esperanza, GESPIC, OASIS, Reuma.pt, SCQM, SPACE, UCSF). Subsequently, we calculated the percentage of patients who fulfilled the ASAS r-axSpA criteria within the group of patients who fulfilled the mNY criteria and vice versa in six cohorts with complete information.ResultsOf the 3882 patients fulfilling the mNY criteria, 93% also fulfilled the ASAS r-axSpA criteria. Inversely, of the 3434 patients fulfilling the ASAS r-axSpA criteria, 96% also fulfilled the mNY criteria. The main cause for discrepancy between the two criteria sets was the reported age at onset of back pain.ConclusionAlmost all patients with axSpA with radiographic sacroiliitis fulfil both ASAS and mNY criteria, which supports the interchangeable use of the terms AS and r-axSpA.

ObjectivesTo investigate the extent and performance of MRI lesions in the sacroiliac joint (MRI-SI) and spine (MRI-spine) in patients with suspected axial spondyloarthritis (axSpA).MethodsMRI-SI/spine of patients with chronic back pain (onset <45 years) in the SPondyloArthritis Caught Early (SPACE) cohort were scored by two well-trained readers for inflammation, fatty lesions, erosions, sclerosis/ankylosis and syndesmophytes. MRI performances were tested against the Assessment of Spondyloarthritis international Society (ASAS) axSpA criteria (positive: imaging-arm+ or clinical-arm+; negative: possible axSpA (few spondyloarthritis (SpA) features present) or no SpA). Arbitrary cut-off levels for MRI lesions were set to assure at least 95% specificity (tested in the no SpA group).ResultsIn total 126 patients were ASAS criteria positive (73 imaging-arm+ (22 by modified New York criteria (mNY)+; 51 by MRI+mNY−); 53 clinical-arm+) and 161 were ASAS criteria negative (89 possible axSpA and 72 no SpA). On MRI-SI (n=287), at least three fatty lesions (or at least three erosions) were seen in 45.5 (63.6)% of mNY+ patients, 15.7 (47.1)% of MRI+mNY− patients and 15.1 (13.2)% of clinical-arm+ patients versus 3.4 (6.7)% of possible axSpA patients and 2.8 (4.2)% of no SpA patients. A combined rule (at least five fatty lesions and/or erosions) performed equally well. Sclerosis and ankylosis were too rare to analyse. On MRI-spine (n=284), at least five inflammatory lesions (or at least five fatty lesions) were seen in 27.3 (18.2)% of mNY+ patients, 13.7 (21.6)% of MRI+mNY− patients and 3.8 (1.9)% of clinical-arm+ patients versus 4.5 (6.7)% of possible SpA patients and 2.9 (4.3)% of no SpA patients.ConclusionsThe presence of (1) at least five fatty lesions and/or erosions on MRI-SI, (2) at least five inflammatory lesions or (3) at least five fatty lesions on MRI-spine allows an acceptable discrimination of axSpA and no SpA, while assuring >95% specificity.

BackgroundA range of sacroiliac joint (SIJ) MRI protocols are used in clinical practice but not all were specifically designed for diagnostic ascertainment. This can be confusing and no standard diagnostic SIJ MRI protocol is currently accepted worldwide.ObjectiveTo develop a standardised MRI image acquisition protocol (IAP) for diagnostic ascertainment of sacroiliitis.Methods13 radiologist members of Assessment of SpondyloArthritis International Society (ASAS) and the SpondyloArthritis Research and Treatment Network (SPARTAN) plus two rheumatologists participated in a consensus exercise. A draft IAP was circulated with background information and online examples. Feedback on all issues was tabulated and recirculated. The remaining points of contention were resolved and the revised IAP was presented to the entire ASAS membership.ResultsA minimum four-sequence IAP is recommended for diagnostic ascertainment of sacroiliitis and its differential diagnoses meeting the following requirements. Three semicoronal sequences, parallel to the dorsal cortex of the S2 vertebral body, should include sequences sensitive for detection of (1) changes in fat signal and structural damage with T1-weighting; (2) active inflammation, being T2-weighted with fat suppression; (3) bone erosion optimally depicting the bone–cartilage interface of the articular surface and (4) a semiaxial sequence sensitive for detection of inflammation. The IAP was approved at the 2022 ASAS annual meeting with 91% of the membership in favour.ConclusionA standardised IAP for SIJ MRI for diagnostic ascertainment of sacroiliitis is recommended and should be composed of at least four sequences that include imaging in two planes and optimally visualise inflammation, structural damage and the bone–cartilage interface.