Frequency and Anatomic Distribution of Magnetic Resonance Imaging Features in the Sacroiliac Joints of Young Athletes: Exploring "Background Noise" Toward a Data-Driven Definition of Sacroiliitis in Early Spondyloarthritis

Imaging of Sacroiliac Pain: The Current State-of-the-Art

Pain in the sacroiliac (SI) region is a common clinical manifestation, often caused by diseases involving the SI joints. This is typically due to inflammation or degenerative changes, while infections or cancer are less frequent causes. The SI joint is challenging to image accurately because of its distinct anatomical characteristics. For an accurate diagnosis, conventional radiography often needs to be supplemented with more precise methods such as magnetic resonance imaging (MRI) or computed tomography (CT). Sacroiliitis, a common presenting feature of axial spondyloarthritis (axial SpA), manifests as bone marrow edema, erosions, sclerosis, and joint space narrowing. Septic sacroiliitis and repetitive stress injuries in sports can also cause changes resembling inflammatory sacroiliitis. Other conditions, such as osteitis condensans ilii (OCI), can mimic the radiologic characteristics of sacroiliitis. Inflammatory lesions are diagnosed by concurrent erosions, hyperostosis, and ankylosis. Ligament ossifications or mechanical stress can also result in arthritic disorders. Determining the exact diagnosis can be aided by the distribution of the lesions. Inflammatory lesions can affect any part of the articulation, including the inferior and posterior portions. Mechanical lesions, such as those seen in OCI, often occur in the anterior middle region of the joint. In cases of idiopathic skeletal hyperostosis, ligament ossification is found at the joint borders. This pictorial essay describes common SI joint problems, illustrated with multimodal imaging data. We, also, discuss strategies for selecting the best imaging modalities, along with imaging pitfalls, key points, and approaches for treating patients with suspected inflammatory back pain.

Standardized reporting of spine and sacroiliac joints in axial spondyloarthritis MRI: from the ESSR-Arthritis Subcommittee

OBJECTIVES

Apply a modified Delphi-based approach and produce a practical, radiology-specific set of definitions for interpretation and standardization of the multiple MRI findings in axial spondyloarthritis (ax-SpA), specifically to aid the general radiologist with a musculoskeletal interest, working with gold standard basic MRI protocols.

MATERIALS AND METHODS

We report the results of a modified Delphi-based consensus of 35 experts from 13 countries in the Arthritis Subcommittee of the European Society of Musculoskeletal Radiology (ESSR). Seventeen definitions were created (i.e., nine for the spine and eight for the sacroiliac joint) and two Delphi rounds were conducted on an electronic database, collated and revised by the project leader with agreement. Group leads were appointed for each definition following the first round. Final definitions included only those that reached a consensus > 80%; if > 50% agreed on exclusion consensus, definitions were excluded. Final results have been shared during the Arthritis meeting at the Annual ESSR Congress.

RESULTS

Fourteen definitions, eight for the spine and six for the sacroiliac joint were agreed for standardized reporting. Andersson's, anterior corner sclerotic and costovertebral joint inflammatory lesions of the spine, with active and non-active erosions, and fat metaplasia of the sacroiliac joint reaching the highest consensus (≥ 95%). More than 50% of the experts agreed to exclude joint space inflammation in the sacroiliac joint and tissue backfill. Syndesmophytes reached 76% agreement.

CONCLUSIONS

Agreed definitions by expert radiologists using a modified Delphi process, should allow standardized actionable radiology reports and clarity in reporting terminology of ax-SpA.

CLINICAL RELEVANCE STATEMENT

The proposed definitions will support reporting from musculoskeletal and general radiologists working with gold-standard basic MRI, improve confidence in lesion assessment, and standardize terminology to provide actionable reports on MRI in patients with ax-SpA.

KEY POINTS

Experts applied a modified Delphi method to optimize the definitions of MRI findings of ax-SpA. After two Delphi rounds and one in-person meeting, fourteen definitions reached the agreement threshold. These consensus-based definitions will aid in actionable reporting specifically for the general radiologist with a musculoskeletal interest.

Magnetic Resonance Imaging Topography of Bone Marrow Edema in the Sacroiliac Joint of Postpartum Women

OBJECTIVE

A traditional monoplanar semicoronal and a biplanar magnetic resonance imaging (MRI) assessment method were used to compare the topographical distribution of postpartum strain-related bone marrow edema (BME) at the sacroiliac joint (SIJ).

METHODS

The presence and topographical location of SIJ BME were assessed independently by three readers in 71 women 12 months postpartum. A traditional monoplanar semicoronal and a biplanar BME evaluation by 8 (upper and lower) and 12 joint (upper, middle, and lower) regions, respectively, was performed with >4 weeks between the two assessments. Descriptive results were reported as mean ± SD and ranges, and interreader agreement by intraclass correlation coefficient (ICC).

RESULTS

By semicoronal assessment, 38 (53.5%) women had BME with a mean ± SD SPARCC score of 2.3 ± 4.0 (range 0-22; ICC 0.93, 95% confidence interval [CI] 0.92-0.94). Forty-one (57.8%) had BME by biplanar assessment with a mean ± SD sum score of 2.9 ± 5.8 (range 0-32.7; ICC 0.89, 95% CI 0.88-0.91). By semicoronal assessment, the highest frequency and mean SPARCC scores were in the anterior upper regions of ilium (24%, mean 0.6) and sacrum (21%, mean 0.3) followed by the posterior upper sacral (20%, mean 0.4) and posterior lower iliac (20%, mean 0.3) regions. By biplanar assessment, the anterior middle joint regions had highest BME frequency and sum scores, sacral side (32%, mean 1.9) and iliac side (27%, mean 2.0), respectively; frequencies and sum scores were generally higher in the anterior compared to the posterior joint regions.

CONCLUSION

The 12-region biplanar assessment revealed a predominantly anterior middle location of postpartum SIJ BME whereas the 8-region monoplanar approach did not demarcate distinct strain-prone SIJ regions. Complementing traditional monoplanar semicoronal SIJ MRI evaluation by a semiaxial assessment may facilitate discrimination of strain-related conditions from early axial spondyloarthritis.

Axial Spondyloarthritis: Does Magnetic Resonance Imaging Classification Improve Report Interpretation

OBJECTIVE

The interpretation of magnetic resonance imaging (MRI) reports is crucial for the diagnosis of axial spondyloarthritis, but the subjective nature of narrative reports can lead to varying interpretations. This study presents a validation of a novel MRI reporting system for the sacroiliac joint in clinical practice.

METHODS

A historical review was conducted on 130 consecutive patients referred by 2 rheumatologists for initial MRI assessment of possible axial spondyloarthritis. The original MRI reports were interpreted by the rheumatologists and the radiologist who originally read the images and then categorized according to the novel system. Two musculoskeletal radiologists then reinterpreted the original MRI scans using the new system, and the resulting reports were interpreted and categorized by the same rheumatologists. The quality of the new framework was assessed by comparing the interpretations of both reports.

RESULTS

Ninety-two patients met the study criteria. The rheumatologists disagreed on the categorization of the original MRI reports in 12% of cases. The rheumatologists and original radiologists disagreed on the categorization of the initial report in 23.4% of cases. In contrast, there was 100% agreement between the rheumatologists and radiologists on the categorization of the new MRI report.

CONCLUSION

The new MRI categorization system significantly improved the agreement between the clinician and radiologist in report interpretation. The system provided a standard vocabulary for reporting, reduced variability in report interpretation, and may therefore improve clinical decision-making.

The bright Easter bunny sign: a useful aide-memoire on MRI for costotransverse joint inflammation in axial spondyloarthritis

AIM

To assess the significance of the "bright Easter bunny" sign on magnetic resonance imaging (MRI) to indicate inflammatory costotransverse joint (CtJ) lesions to diagnose axial spondyloarthritis (ax-SpA).

MATERIALS AND METHODS

Consecutive cases of patients with ax-SpA from a specialist rheumatology clinic were analysed retrospectively over two cohorts, between 2012-2014 and 2018-2020, to determine newly diagnosed patients under the Assessment of SpondyloArthritis international Society (ASAS) criteria. Biological naive adult patients who underwent spine MRI and sacroiliac imaging with full immunological work-up and a C-reactive protein reading within 3 months of the scan were included. Blinded images were reviewed by experienced musculoskeletal radiologists.

RESULT

From the 1,284 cases that were identified, 40 cases met the inclusion criteria for this study. Seven out of the 40 cases (17.5%) identified inflammatory lesions at the CtJ with five (70%) showing concordance with the bright Easter bunny sign.

CONCLUSION

The bright Easter bunny sign is concordant with inflammatory costotransverse enthesitis. This aide-memoire radiological sign is often on overlooked edge-of-field sections and this emphasises the need to ensure adequate coverage of the CtJ on spine MRI protocols as an important anatomical site of inflammatory change in ax-SpA assessment.

The sacroiliac joint across ages - what is normal?

The anatomy of the sacroiliac joint (SIJ) is complex with wide variations inter-individually as well as intra-individually (right versus left) and a frequent occurrence of anatomical variants. Besides, the joints are subject to strain, which may elicit non-inflammatory subchondral changes such as bone marrow edema (BME), sclerosis, and fat deposition simulating inflammatory SIJ changes. Furthermore, normal physiological changes during skeletal maturation can make interpretation of SIJ magnetic resonance imaging in children challenging. Knowledge about the wide range of normal findings is therefore important to avoid misinterpretation of findings as pathological. This review describes the current knowledge about normal SIJ findings across all ages.

Use of MRI-based deep learning radiomics to diagnose sacroiliitis related to axial spondyloarthritis

OBJECTIVES

This study aimed to evaluate the performance of a deep learning radiomics (DLR) model, which integrates multimodal MRI features and clinical information, in diagnosing sacroiliitis related to axial spondyloarthritis (axSpA).

MATERIAL & METHODS

A total of 485 patients diagnosed with sacroiliitis related to axSpA (n = 288) or non-sacroiliitis (n = 197) by sacroiliac joint (SIJ) MRI between May 2018 and October 2022 were retrospectively included in this study. The patients were randomly divided into training (n = 388) and testing (n = 97) cohorts. Data were collected using three MRI scanners. We applied a convolutional neural network (CNN) called 3D U-Net for automated SIJ segmentation. Additionally, three CNNs (ResNet50, ResNet101, and DenseNet121) were used to diagnose axSpA-related sacroiliitis using a single modality. The prediction results of all the CNN models across different modalities were integrated using a stacking method based on different algorithms to construct ensemble models, and the optimal ensemble model was used as DLR signature. A combined model incorporating DLR signature with clinical factors was developed using multivariable logistic regression. The performance of the models was evaluated using receiver operating characteristic (ROC) curves, calibration curves, and decision curve analysis (DCA).

RESULTS

Automated deep learning-based segmentation and manual delineation showed good correlation. ResNet50, as the optimal basic model, achieved an area under the curve (AUC) and accuracy of 0.839 and 0.804, respectively. The combined model yielded the highest performance in diagnosing axSpA-related sacroiliitis (AUC: 0.910; accuracy: 0.856) and outperformed the best ensemble model (AUC: 0.868; accuracy: 0.825) (all P < 0.05). Moreover, the DCA showed good clinical utility in the combined model.

CONCLUSION

We developed a diagnostic model for axSpA-related sacroiliitis by combining the DLR signature with clinical factors, which resulted in excellent diagnostic performance.

Association between sacroiliac joint forms and subchondral changes in patients with Crohn's disease

AIM

To assess the relationship between anatomical variants of sacroiliac joint (SIJ) and subchondral changes detected in magnetic resonance enterography (MRE) in patients with Crohn's disease (CD).

METHODS

This was a retrospective study of 60 CD patients, who were divided into two groups: with (n = 16) and without SIJ (n = 44) involvement, depending on the presence of inflammatory (bone marrow edema) and structural changes (sclerosis and erosions) in MRE. Anatomical variants of SIJ were assessed in CT of the abdomen and/or pelvis, distinguishing typical form with convex iliac surface and atypical forms. Univariate and multivariate analyses were performed to reveal an association between joint changes and forms.

RESULTS

Our study included 60 patients (38 males; mean age 38.72 years ± 13.33). Patients with SIJ changes were older (p = .044). No significant differences in CD localization and behavior were found. The most common SIJ lesions were structural changes (in 75% of patients); the main atypical form was the iliosacral complex. The univariate and multivariate analyses showed a significant association of atypical forms with total subchondral changes (odds ratio [OR]: 3.429, 95% confidence interval [CI] 1.043-11.268; p = .042; OR: 5.066, 95% CI: 1.273-20.167; p = .021, respectively), and with structural changes (OR: 4.185, 95% CI: 1.155-15.160; p = .029; OR: 5.986, 95% CI: 1.293-27.700; p = .022, respectively).

CONCLUSION

Atypical forms of SIJ are a risk factor for the occurrence of structural joint changes in CD patients. An association between bone marrow edema and atypical forms was not found.

Prognostic value of the clinical and imaging arm of the ASAS criteria for progression of structural sacroiliac joint lesions

OBJECTIVE

To investigate the prognostic value of the two arms of the Assessment of SpondyloArthritis international Society (ASAS) criteria regarding the progression of structural lesions in the sacroiliac joints (SIJs).

METHODS

Information on baseline fulfilment of the ASAS criteria and baseline and follow-up magnetic resonance imaging of the SIJ in 603 patients aged 18-40 years referred with low back pain to an outpatient spine were collected. Magnetic resonance imaging positivity was defined as bone marrow oedema (BMO) in two or more consecutive slices or two or more lesions in one slice, as described in the ASAS definition of sacroiliitis.

RESULTS

Of 71 participants fulfilling the ASAS criteria at baseline, 66 (93%) fulfilled the 'imaging arm' and 14 (20%) fulfilled the 'clinical arm'. The 'clinical arm' predicted the progression of erosions with an odds ratio of 55 (compared with not fulfilling the ASAS criteria), while the 'imaging arm' predicted the progression of erosions with an odds ratio of 8. Moreover, in 24% of the patients in the 'imaging arm', all having BMO at the SIJ at baseline, the BMO disappeared without neither erosions nor ankylosis emerging.

CONCLUSION

We found that the 'clinical arm' was a strong predictor for the progression of SIJ erosion, while the 'imaging arm' had a more modest prognostic value for structural progression.

The Role of Early Treatment in the Management of Axial Spondyloarthritis: Challenges and Opportunities

Axial spondyloarthritis (axSpA) is a chronic, inflammatory rheumatic disease that primarily affects the axial skeleton, often inflicting severe pain, diminished mobility, and a compromised quality of life. The advent of Assessment of SpondyloArthritis international Society (ASAS) classification criteria for spondyloarthritis (SpA) have enabled the classification of patients with axSpA in the non-radiographic stage but poorly perform if mistakenly used for diagnostic purposes. Despite notable progress in early diagnosis facilitated by referral strategies and extensive magnetic resonance imaging (MRI) utilization, diagnostic delays persist as a concerning issue. This underscores the urgency to narrow the diagnostic gap and highlights the critical role of early diagnosis in mitigating the long-term structural damage associated with this condition. Research into the impact of non-steroidal anti-inflammatory drugs (NSAIDs) and biologic disease-modifying antirheumatic drugs (bDMARDs) on inflammatory symptoms and radiographic progression has been extensive. A compelling body of evidence suggests that early intervention leads to superior disease outcomes. However, most of these studies have centered on patients with established diseases rather than those in the early stages. Consequently, findings from studies on early pharmacological intervention remain inconclusive, and the potential for modifying the disease trajectory is still debatable. Without precise data from clinical trials, insights from basic science regarding the pathogenic mechanisms might point toward potential targets that warrant early intervention in the disease process. This review underscores the urgency of early diagnosis and intervention in axSpA, highlighting ongoing research gaps and the need for further exploration to improve patient outcomes.

Research on automatic recognition radiomics algorithm for early sacroiliac arthritis based on sacroiliac MRI imaging

OBJECTIVE

To create an automated machine learning model using sacroiliac joint MRI imaging for early sacroiliac arthritis detection, aiming to enhance diagnostic accuracy.

METHODS

We conducted a retrospective analysis involving 71 patients with early sacroiliac arthritis and 85 patients with normal sacroiliac joint MRI scans. Transverse T1WI and T2WI sequences were collected and subjected to radiomics analysis by two physicians. Patients were randomly divided into training and test groups at a 7:3 ratio. Initially, we extracted the region of interest on the sacroiliac joint surface using ITK-SNAP 3.6.0 software and extracted radiomic features. We retained features with an Intraclass Correlation Coefficient > 0.80, followed by filtering using max-relevance and min-redundancy (mRMR) and LASSO algorithms to establish an automatic identification model for sacroiliac joint surface injury. Receiver operating characteristic (ROC) curves were plotted, and the area under the ROC curve (AUC) was calculated. Model performance was assessed by accuracy, sensitivity, and specificity.

RESULTS

We evaluated model performance, achieving an AUC of 0.943 for the SVM-T1WI training group, with accuracy, sensitivity, and specificity values of 0.878, 0.836, and 0.943, respectively. The SVM-T1WI test group exhibited an AUC of 0.875, with corresponding accuracy, sensitivity, and specificity values of 0.909, 0.929, and 0.875, respectively. For the SVM-T2WI training group, the AUC was 0.975, with accuracy, sensitivity, and specificity values of 0.933, 0.889, and 0.750. The SVM-T2WI test group produced an AUC of 0.902, with accuracy, sensitivity, and specificity values of 0.864, 0.889, and 0.800. In the SVM-bimodal training group, we achieved an AUC of 0.974, with accuracy, sensitivity, and specificity values of 0.921, 0.889, and 0.971, respectively. The SVM-bimodal test group exhibited an AUC of 0.964, with accuracy, sensitivity, and specificity values of 0.955, 1.000, and 0.875, respectively.

CONCLUSION

The radiomics-based detection model demonstrates excellent automatic identification performance for early sacroiliitis.

Sacroiliac joint MRI for diagnosis of ax-SpA: algorithm to improve the specificity of the current ASAS MRI criteria

OBJECTIVE

To compare sacroiliac joint (SIJ) lesions on MRI in women with versus without axial spondyloarthritis (ax-SpA) and establish an algorithm to determine whether such lesions are due to ax-SpA.

METHODS

This retrospective comparative study assessed bone marrow edema (BME), sclerosis, erosions, osteophytes, and ankylosis at the SIJ in two groups of women, one with and another without ax-SpA. Sensitivity and specificity were calculated for combinations/characteristics of lesions, using rheumatologists' assessment with assessment of spondyloarthritis international society (ASAS) criteria as the gold standard for diagnosis of ax-SpA.

RESULTS

Compared to women without ax-SpA, women with ax-SpA had more BME (61% vs 17%, p < 0.001), sclerosis (40% vs 22%, p < 0.001), erosions (35% vs 5%, p < 0.001), and ankylosis (2% vs 0%, p = 0.007), but less osteophytes (5% vs 33%, p < 0.001). The ASAS MRI criteria yielded 59% sensitivity and 88% specificity, while a new algorithm achieved 56% sensitivity and 95% specificity using the following criteria: no osteophytes at the SIJ and either (i) BME at the SIJ with at least one dimension ≥ 8 mm or (ii) at least one erosion at the SIJ.

CONCLUSIONS

We recommend the following pragmatic algorithm for MRI diagnosis of ax-SpA in women: no osteophytes at the SIJ and either (i) BME at the SIJ with at least one dimension ≥ 8 mm or (ii) at least one erosion at the SIJ. The false positive rate when using the new algorithm (3.3%) is less than half than when using the ASAS MRI criteria (7.7%); thus, its application in clinical practice could reduce overdiagnosis and prevent overtreatment of ax-SpA.

CLINICAL RELEVANCE STATEMENT

The developed algorithm has a false-positive rate that is less than half than when using the ASAS MRI criteria (3.3% vs 7.7%), thus its application in clinical practice could reduce overdiagnosis and prevent overtreatment of axial spondyloarthritis.

KEY POINTS

• Compared to women without axial spondyloarthritis (ax-SpA), women with ax-SpA had a significantly higher prevalence of bone marrow edema (BME), sclerosis, erosions, and ankylosis, but a significantly lower prevalence of osteophytes. • A new algorithm for positive ax-SpA based on sacroiliac joint MRI was developed: no osteophytes at the sacroiliac joint (SIJ) and either (i) BME at the SIJ with at least one dimension ≥ 8 mm or (ii) at least one erosion at the SIJ. • We recommend this new algorithm for diagnosis of ax-SpA in women, as it has a significantly better specificity than the assessment of spondyloarthritis international society (ASAS) MRI criteria and less than half the false positive rate; thus, its application in clinical practice could reduce overdiagnosis and prevent overtreatment of ax-SpA.

Artificial intelligence for the detection of sacroiliitis on magnetic resonance imaging in patients with axial spondyloarthritis

Background

Magnetic resonance imaging (MRI) is important for the early detection of axial spondyloarthritis (axSpA). We developed an artificial intelligence (AI) model for detecting sacroiliitis in patients with axSpA using MRI.

Methods

This study included MRI examinations of patients who underwent semi-coronal MRI scans of the sacroiliac joints owing to chronic back pain with short tau inversion recovery (STIR) sequences between January 2010 and December 2021. Sacroiliitis was defined as a positive MRI finding according to the ASAS classification criteria for axSpA. We developed a two-stage framework. First, the Faster R-CNN network extracted regions of interest (ROIs) to localize the sacroiliac joints. Maximum intensity projection (MIP) of three consecutive slices was used to mimic the reading of two adjacent slices. Second, the VGG-19 network determined the presence of sacroiliitis in localized ROIs. We augmented the positive dataset six-fold. The sacroiliitis classification performance was measured using the sensitivity, specificity, and area under the receiver operating characteristic curve (AUROC). The prediction models were evaluated using three-round three-fold cross-validation.

Results

A total of 296 participants with 4,746 MRI slices were included in the study. Sacroiliitis was identified in 864 MRI slices of 119 participants. The mean sensitivity, specificity, and AUROC for the detection of sacroiliitis were 0.725 (95% CI, 0.705-0.745), 0.936 (95% CI, 0.924-0.947), and 0.830 (95%CI, 0.792-0.868), respectively, at the image level and 0.947 (95% CI, 0.912-0.982), 0.691 (95% CI, 0.603-0.779), and 0.816 (95% CI, 0.776-0.856), respectively, at the patient level. In the original model, without using MIP and dataset augmentation, the mean sensitivity, specificity, and AUROC were 0.517 (95% CI, 0.493-0.780), 0.944 (95% CI, 0.933-0.955), and 0.731 (95% CI, 0.681-0.780), respectively, at the image level and 0.806 (95% CI, 0.729-0.883), 0.617 (95% CI, 0.523-0.711), and 0.711 (95% CI, 0.660-0.763), respectively, at the patient level. The performance was improved by MIP techniques and data augmentation.

Conclusion

An AI model was developed for the detection of sacroiliitis using MRI, compatible with the ASAS criteria for axSpA, with the potential to aid MRI application in a wider clinical setting.

A mixed methods study to uncover impediments to accurate diagnosis of nonradiographic axial spondyloarthritis in the USA

INTRODUCTION/OBJECTIVES

Delayed diagnosis of axial spondyloarthritis (axSpA) is well documented; little is known about the diagnostic journey and impediments for US patients with nonradiographic axSpA (nr-axSpA). It is hypothesized that impediments are varied and exist at both the healthcare provider (HCP) and patient levels. This study aims to understand patient experiences and contributors to delayed nr-axSpA diagnosis in the USA.

METHOD

Interviews of adults with rheumatologist-diagnosed nr-axSpA, recruited through Spondylitis Association of America outreach and patient panels, and of rheumatologists, explored the diagnostic journey and diagnostic barriers. Emerging themes were further explored in an online patient survey. A multiple logistic regression analysis evaluated the main outcome variable, factors affecting time to nr-axSpA diagnosis.

RESULTS

Interviews were conducted with 25 patients and 16 rheumatologists. Survey responses from 186 eligible patients revealed median time from symptom onset to diagnosis of nr-axSpA was 3.25 years. Delayed diagnosis was significantly more likely for women and people in rural areas. Most patients consulted ≥4 different types of HCPs before a rheumatologist and ≥2 rheumatologists before diagnosis. Impediments to timely diagnosis included insidious chronic pain; episodic symptom patterns attributed to activity; symptoms other than chronic lumbosacral back pain requiring medical consultation; and unfamiliarity with and misperceptions about nr-axSpA among HCPs, radiologists, and rheumatologists.

CONCLUSIONS

Delayed nr-axSpA diagnosis is common and reflects HCP knowledge gaps and frequent patient presentation with dominant nonaxial symptoms. Targeted HCP education, research into early disease patterns, and interventions sensitive to the broader spectrum of nr-axSpA manifestations are needed to improve timely diagnosis. Key Points • Patients with nr-axSpA often see multiple types of HCPs, and multiple rheumatologists, before receiving a diagnosis. • Both patients and HCPs are unfamiliar with nr-axSpA and its symptoms, lacking understanding that nr-axSpA can occur in young people, females, and those presenting with normal x-rays. • Disease recognition by nonrheumatology HCPs is key for early referral. • Education on cardinal features, epidemiology, burden, and benefits of timely nr-axSpA diagnosis is warranted for HCPs who commonly manage back pain.

Magnetic resonance imaging in spondyloarthritis: Friend or Foe?

Magnetic resonance imaging (MRI) has emerged as a valuable tool for early detection and of axial spondyloarthritis (axSpA). A standardized imaging acquisition protocol, aligned with the current state-of-the-art, is crucial to obtain MRI scans that meet the diagnostic quality requirements. It is important to note that certain lesions, particularly bone marrow edema (BME), can be induced by mechanical stress or be a manifestation of another non-inflammatory disorder and may mimic the characteristic findings of axSpA on MRI. Therefore, a thorough assessment of MRI lesions, considering their localization and presence of highly specific features such as erosions and backfill, becomes imperative. Additionally, the application of additional imaging modalities, when necessary, can contribute to the differentiation of axSpA from other conditions that may exhibit similar MRI findings. This review provides recommendations on how to perform MRI in daily clinical practice and how to interpret finding from the differential diagnostic point of view.

Challenges in the diagnosis of axial spondyloarthritis

With back pain as one of the most common complaints in the population and with no single disease feature with sufficient sensitivity and specificity to diagnose axial spondyloarthritis (axSpA) on its own, diagnosing axSpA can be challenging. In this article, we discuss clinical, laboratory, and imaging spondyloarthritis features that can be used in diagnosis and explain the general principles underlying an axSpA diagnosis. Moreover, we discuss three pitfalls to avoid when diagnosing axSpA: i) using classification criteria as diagnostic criteria, ii) making a diagnosis by simple counting of spondyloarthritis features, and iii) over-reliance on imaging findings. Finally, we have some advice on how to build diagnostic skills and discuss new developments that may help facilitate the diagnosis of axSpA in the future.

The bone marrow side of axial spondyloarthritis

Spondyloarthritis (SpA) is characterized by the infiltration of innate and adaptive immune cells into entheses and bone marrow. Molecular, cellular and imaging evidence demonstrates the presence of bone marrow inflammation, a hallmark of SpA. In the spine and the peripheral joints, bone marrow is critically involved in the pathogenesis of SpA. Evidence suggests that bone marrow inflammation is associated with enthesitis and that there are roles for mechano-inflammation and intestinal inflammation in bone marrow involvement in SpA. Specific cell types (including mesenchymal stem cells, innate lymphoid cells and γδ T cells) and mediators (Toll-like receptors and cytokines such as TNF, IL-17A, IL-22, IL-23, GM-CSF and TGFβ) are involved in these processes. Using this evidence to demonstrate a bone marrow rather than an entheseal origin for SpA could change our understanding of the disease pathogenesis and the relevant therapeutic approach.

Imaging in pediatric spondyloarthritis

PURPOSE OF REVIEW

Imaging is used in the diagnosis of peripheral and axial disease in juvenile spondyloarthritis (JSpA). Imaging of the joints and entheses in children and adolescents can be challenging for those unfamiliar with the appearance of the maturing skeleton. These differences are key for rheumatologists and radiologists to be aware of.

RECENT FINDINGS

In youth, skeletal variation during maturation makes the identification of arthritis, enthesitis, and sacroiliitis difficult. A great effort has been put forward to define imaging characteristics seen in healthy children in order to more accurately identify disease. Additionally, there are novel imaging modalities on the horizon that are promising to further differentiate normal physiologic changes versus disease.

SUMMARY

This review describes the current state of imaging, limitations, and future imaging modalities in youth, with key attention to differences in imaging interpretation of the peripheral joints, entheses, and sacroiliac joint in youth and adults.

MRI in pediatric sacroiliitis, what radiologists should know

MRI is used for early detection of inflammation of sacroiliac joints as it shows active lesions of sacroiliitis long before radiographs show damage to the sacroiliac joints. Early diagnosis of arthritis allows early treatment of inflammation and can help delay disease progression and prevent irreversible damage. Also, early identification of axial involvement in juvenile spondyloarthropathy is crucial, as treatment options are different than for peripheral juvenile spondyloarthropathy. In general, standard sequences used in adults are also applied to children. However, interpreting MR images of pediatric sacroiliac joints is more challenging than in adults, because of normal physiological changes during skeletal maturation, which can simulate disease on MR images. Furthermore, classical definitions of sacroiliitis used in adults, for both active inflammatory and structural lesions, can be difficult to extrapolate to children. The development of reliable pediatric-specific definitions for sacroiliitis is still in active study. Understanding both normal and pathological signal changes in children is important to distinguish physiologic findings from disease and to make a correct diagnosis. In this review, the main imaging characteristics of sacroiliitis on MRI in children and its frequent pitfalls will be illustrated, while also citing some discussion points regarding the scan protocol.

Data-Driven Magnetic Resonance Imaging Definitions for Active and Structural Sacroiliac Joint Lesions in Juvenile Spondyloarthritis Typical of Axial Disease: A Cross-Sectional International Study

OBJECTIVE

We aimed to determine quantitative sacroiliac (SI) joint magnetic resonance imaging (MRI) cutoffs for active and structural lesions that will be incorporated as imaging domains in classification criteria of axial disease in juvenile spondyloarthritis (SpA).

METHODS

MRI scans from an international cross-section of juvenile SpA patients were reviewed by 6 musculoskeletal imaging experts blinded to clinical details. Raters globally assessed the presence/absence of lesions typical of axial SpA and performed SI joint quadrant- or joint-based scoring. Sensitivity and specificity of lesion cutoffs were calculated using a rater majority (≥4 of 6 raters) on a global assessment of the presence/absence of active or structural lesions typical of axial SpA with high confidence as the reference standard. Cutoffs were validated in an independent cohort.

RESULTS

Imaging from 243 subjects, 61% male, median age 14.9 years, had sequences available for detailed MRI scoring. Optimal cutoffs for defining lesions typical of axial disease in juvenile SpA were: 1) inflammatory lesion: bone marrow edema in ≥3 SI joint quadrants across all SI joint MRI slices (sensitivity 98.6%, specificity 96.5%); 2) structural lesions: erosion in ≥3 quadrants or sclerosis or fat lesion in ≥2 SI joint quadrants or backfill or ankylosis in ≥2 joint halves across all SI joint MRI slices (sensitivity 98.6%, specificity 95.5%). Sensitivity and specificity of the optimal cutoffs in the validation cohort were excellent.

CONCLUSION

We propose data-driven cutoffs for active inflammatory and structural lesions on MRI typical of axial disease in juvenile SpA that have high specificity and sensitivity using central imaging global assessment as the reference standard and excellent reliability.

Data-Driven Magnetic Resonance Imaging Definitions for Active and Structural Sacroiliac Joint Lesions in Juvenile Spondyloarthritis Typical of Axial Disease: A Cross-Sectional International Study

OBJECTIVE

We aimed to determine quantitative sacroiliac (SI) joint magnetic resonance imaging (MRI) cutoffs for active and structural lesions that will be incorporated as imaging domains in classification criteria of axial disease in juvenile spondyloarthritis (SpA).

METHODS

MRI scans from an international cross-section of juvenile SpA patients were reviewed by 6 musculoskeletal imaging experts blinded to clinical details. Raters globally assessed the presence/absence of lesions typical of axial SpA and performed SI joint quadrant- or joint-based scoring. Sensitivity and specificity of lesion cutoffs were calculated using a rater majority (≥4 of 6 raters) on a global assessment of the presence/absence of active or structural lesions typical of axial SpA with high confidence as the reference standard. Cutoffs were validated in an independent cohort.

RESULTS

Imaging from 243 subjects, 61% male, median age 14.9 years, had sequences available for detailed MRI scoring. Optimal cutoffs for defining lesions typical of axial disease in juvenile SpA were: 1) inflammatory lesion: bone marrow edema in ≥3 SI joint quadrants across all SI joint MRI slices (sensitivity 98.6%, specificity 96.5%); 2) structural lesions: erosion in ≥3 quadrants or sclerosis or fat lesion in ≥2 SI joint quadrants or backfill or ankylosis in ≥2 joint halves across all SI joint MRI slices (sensitivity 98.6%, specificity 95.5%). Sensitivity and specificity of the optimal cutoffs in the validation cohort were excellent.

CONCLUSION

We propose data-driven cutoffs for active inflammatory and structural lesions on MRI typical of axial disease in juvenile SpA that have high specificity and sensitivity using central imaging global assessment as the reference standard and excellent reliability.

Axial Skeleton Bone Marrow Changes in Inflammatory Rheumatologic Disorders

Magnetic resonance imaging (MRI) of the axial skeleton, spine, and sacroiliac (SI) joints is critical for the early detection and follow-up of inflammatory rheumatologic disorders such as axial spondyloarthritis, rheumatoid arthritis, and SAPHO/CRMO (synovitis, acne, pustulosis, hyperostosis, and osteitis/chronic recurrent multifocal osteomyelitis). To offer a valuable report to the referring physician, disease-specific knowledge is essential. Certain MRI parameters can help the radiologist provide an early diagnosis and lead to effective treatment. Awareness of these hallmarks may help avoid misdiagnosis and unnecessary biopsies. A bone marrow edema-like signal plays an important role in reports but is not disease specific. Age, sex, and history should be considered in interpreting MRI to prevent overdiagnosis of rheumatologic disease. Differential diagnoses-degenerative disk disease, infection, and crystal arthropathy-are addressed here. Whole-body MRI may be helpful in diagnosing SAPHO/CRMO.

Diagnostics of Sacroiliac Joint Differentials to Axial Spondyloarthritis Changes by Magnetic Resonance Imaging

The diagnosis of axial spondyloarthritis (axSpA) is usually based on a pattern of imaging and clinical findings due to the lack of diagnostic criteria. The increasing use of magnetic resonance imaging (MRI) of the sacroiliac joints (SIJ) to establish the diagnosis early in the pre-radiographic phase has resulted in a shift in the paradigm with an increasing frequency of axSpA diagnoses and a changed sex distribution. Non-radiographic axSpA affects males and females nearly equally, whereas ankylosing spondylitis predominantly occurs in males. The MRI-based increasing frequency of axSpA in women is mainly due to the presence of subchondral bone marrow edema (BME) on fluid-sensitive MR sequences, which may be a non-specific finding in both women and men. Due to the somewhat different pelvic tilt and SIJ anatomy, women are more prone than men to develop strain-related MRI changes and may have pregnancy-related changes. Awareness of non-specific subchondral BME at the SIJ is important as it can imply a risk for an incorrect SpA diagnosis, especially as the clinical manifestations of axSpA may also be non-specific. Knowledge of relevant MRI and clinical features of differential diagnoses is needed in the diagnostic workout of patients with suspected axSpA considering that non-SpA-related SIJ conditions are more common in patients with low back or buttock pain than axSpA sacroiliitis. The purpose of this review was to present current knowledge of the most frequent differential diagnoses to axSpA sacroiliitis by MRI taking the clinical characteristics into account.

Challenges in non-radiographic axial spondyloarthritis

Non-radiographic axial spondyloarthritis (nr-axSpA) is part of the spectrum or continuum of axSpA and is characterized by the absence of definite structural damage in the sacroiliac joints. The introduction of the concept of axSpA with two - non-radiographic and radiographic - stages stimulated activities related to the improvement of early diagnosis and treatment of this disease, but also opened a number of controversial topics in the field. In this article, we are discussing several challenges related to the concept of nr-axSpA, the diagnosis, and the treatment in the historical context and in the light of the recent data.

Progression From Subclinical Inflammation to Overt Spondyloarthritis in First-Degree Relatives of Patients in Association With HLA-B27: The Pre-Spondyloarthritis Cohort

OBJECTIVE

As first-degree relatives (FDRs) of HLA-B27-positive patients with axial spondyloarthritis (SpA) have an increased risk of developing axial SpA, the objectives were 1) to evaluate the presence of highly specific imaging features as well as clinical signs of SpA at baseline and after 1 year of follow-up, and 2) to describe the evolution toward clinical disease within 1 year of follow-up in a cohort of seemingly healthy FDRs of HLA-B27-positive axial SpA patients.

METHODS

The Pre-SpA cohort is a 5-year prospective inception cohort of seemingly healthy FDRs of HLA-B27-positive axial SpA patients. Clinical and imaging features were collected and recorded.

RESULTS

At baseline, 19% of the FDRs reported inflammatory back pain, 32% current arthralgia, 3% arthritis (ever), 5% enthesitis (ever), and 1% dactylitis (ever), and 3% had an extraarticular manifestation. C-reactive protein level was elevated in 16%, and erythrocyte sedimentation rate was elevated in 7%. On magnetic resonance imaging (MRI) views of sacroiliac joints, 10% had a Spondyloarthritis Research Consortium of Canada score of ≥2, 4% had a score of ≥5, and 4% had deep lesions. In total, 1% fulfilled the modified New York criteria for radiographic sacroiliitis. Clinical, MRI, and acute phase findings were equally distributed between HLA-B27-positive and -negative FDRs. After 1 year of follow-up, clinical parameters did not change on the group level, but 6% of the FDRs were clinically diagnosed with axial SpA, of whom 86% were HLA-B27-positive.

CONCLUSION

Features associated with SpA or imaging abnormalities were found in up to 32% of seemingly healthy FDRs, with an equal distribution between HLA-B27-positive and -negative FDRs. Progression to clinical axial SpA within 1 year of follow-up was mainly observed in HLA-B27-positive FDRs.

Sacroiliac innervation

PURPOSE

To investigate the innervation pattern of the sacroiliac region, especially with regard to the sacroiliac joint (SIJ). Dorsal SIJ innervation was analyzed and described. Our main hypothesis was that nerves reach the SIJ dorsally, passing ligamental compartments, as this would explain dorsal SIJ pain.

METHODS

To examine sacroiliac innervation, we followed the nerves in over 50 specimens over several years. Plastinated slices were evaluated, nerves in the region were stained histologically, and the data were summarized as 3D models.

RESULTS

The Rami communicans and posterior branches of the spinal nerves and their branches that form a dorsal sacral plexus and communicating branches, together with corresponding vessels, were observed to form neurovascular bundles embedded by tiny fatty connectives in gaps and tunnels. Branches of L5-S1 pass the inner sacroiliac ligaments (the interosseous sacroiliac ligament and axial interosseous ligament). The outer sacroiliac ligaments (posterior sacroiliac ligaments, long posterior sacroiliac ligament, sacrotuberal ligament, thoracolumbar fascia) are passed by the S1-S4 branches. However, although the paths of these nerves are in the direction of the SIJ, they do not reach it. It is possible that impingement of the neurovascular bundles may result in pain. Moreover, the gaps and tunnels connect to the open dorsal SIJ.

CONCLUSION

Our findings suggest that Bogduk's term "sacroiliac pain" correlates to "sacroiliac innervation", which consists of "inner-" and "outer sacroiliac ligament innervation", and to ventral "SIJ pain". The watery gaps and tunnels observed could play a significant role in innervation and thus in the origins of SIJ pain.

LEVEL OF EVIDENCE

Individual cross-sectional studies with consistently applied reference standard and blinding.

Spine abnormalities associated with bone edema on sacroiliac joints MRI in patients with non-inflammatory chronic back pain

OBJECTIVE

To investigate whether bone marrow edema (BME) fulfilling the ASAS definition of magnetic resonance imaging (MRI) sacroiliitis is associated with non-inflammatory spine abnormalities in patients with definite mechanical chronic back pain (CBP).

METHODS

Patients with definite mechanical CBP, according to the physician, started before the age of 45 and be lasting for more than 3months but less than 3years underwent a protocolized MRI and radiographs of sacroiliac joint (SIJ) and spine. BME and structural changes were scored, by three readers, for SIJ as well as non-inflammatory abnormalities for spine, including degenerative lesions and static disorders. Univariate analysis by Chi² test was performed to search a statistical association between BME fulfilling the ASAS definition of MRI sacroiliitis and the presence of at least one non-inflammatory spine abnormality.

RESULTS

A total of 94 patients were analyzed, 27 (29%) patients had BME and 16 (17%) patients had BME fulfilling the ASAS definition of MRI sacroiliitis; 86 (91.5%) patients had at least one non-inflammatory spine abnormality which are associated into 3 distinct clusters. BME was slightly more frequent at the lower and posterior part of the SIJ. MRI sacroiliitis was associated with interspinous bursitis, facet joint effusion and lateral spinal deviation and was more likely in patients with at least one non-inflammatory spine abnormality (OR: 4.96, 95% CI [1.47; 16.72]).

CONCLUSIONS

BME fulfilling the ASAS definition of MRI sacroiliitis is significantly associated with non-inflammatory spine abnormalities in patients with mechanical CBP.

[CME Rheumatology 26: Bone Marrow Edema of the Sacro-Iliac Joint = Spondyloarthritis? What the General Practicioner Should Know]

CME Rheumatology 26: Bone Marrow Edema of the Sacro-Iliac Joint = Spondyloarthritis? What the General Practicioner Should Know Abstract. Axial spondyloarthritis is a chronic inflammatory joint disease mainly involving the sacroiliac joints (ISG) and the spine. The diagnosis can be made early due to acute inflammatory changes in the ISG on magnetic resonance imaging (MRI). Radiographs of the ISG do not help in early diagnosis because structural damage is not apparent on radiographs until an advanced stage. In recent years, however, several studies have shown that bone marrow edema - hyperintense signals (= bright spots) as a possible MRI correlate for inflammation - does not specifically occur in axial spondyloarthritis, but can also be seen in healthy people, athletes, people with high mechanical stress (e.g. military recruits) and postpartum women. The diagnosis of axial spondyloarthritis should therefore never be based solely on an MRI finding, but must always include the overall clinical context.

Sacroiliac joint beyond sacroiliitis-further insights and old concepts on magnetic resonance imaging

The sacroiliac joint (SIJ) is an amphiarthrosis composed of a posterior syndesmosis and an anterior cartilaginous portion, with limited yet present mobility. Its main function is to transmit the load from the axial skeleton to the lower limbs and vice-versa; it is susceptible to early mechanical and degenerative changes which are much more common than inflammatory sacroiliitis. Magnetic resonance imaging (MRI) has increasingly been used to evaluate these changes, and while subchondral bone marrow edema (BME) is a common finding related to both, care must be taken when applying the ASAS research MRI definition for sacroiliitis without considering lesion BME topography, size and depth, concomitant structural damage and, of course, the clinical picture. In this review, we will discuss the anatomy and biomechanics of the SIJ, the noninflammatory causes of SIJ subchondral BME, and how these concepts combined can be used to increase our diagnostic confidence.

Frequency and anatomic distribution of magnetic resonance imaging lesions in the sacroiliac joints of spondyloarthritis and non-spondyloarthritis patients

Background

Lesions detected by magnetic resonance imaging (MRI) of the sacroiliac joints are critical to the diagnosis of non-radiographic axial spondyloarthritis. However, inflammatory and structural lesions may be encountered in other conditions.

Objectives

The objective of this study was to evaluate and compare the frequency and localization of inflammatory and structural lesions on MRIs of the sacroiliac joint of spondyloarthritis (SpA) and non-spondyloarthritis (non-SpA) patients.

Design

This is a retrospective study including 200 patients, each having undergone an MRI of the sacroiliac joints.

Methods

Two experienced readers evaluated the whole set of images to detect erosions, subchondral sclerosis, fatty lesions, bone marrow edema (BME) and ankylosis according to the definitions established by the ASAS MRI working group. We divided sacroiliac joints into five segments: upper, antero-middle, intermediate-middle, postero-middle and lower.

Results

A total of 96 subjects with SpA (mean age 37.4 ± 11.8 years) and 104 without SpA (mean age 39.9 ± 11.6 years) were included. Of the 96 SpA patients, 65% had inflammatory buttock pain compared with 25% in the non-SpA group. BME was seen in 65% of SpA patients, mainly in the intermediate-middle segment, and in 20% of non-SpA patients, predominantly in the antero-middle segment. Subchondral sclerosis occurred in 44% of non-SpA patients, mostly in the antero-middle segment, and in 36% of SpA patients. Fatty lesions were present in 34% of SpA and in 21% of non-SpA patients. Erosions were seen in 25% of non-SpA and in 60% of SpA patients. BME and structural lesions were minimally observed in the postero-middle segment in non-SpA patients.

Conclusion

Inflammatory and structural lesions were observed in all segments of the joint in SpA, mainly in the middle segments, while lesions predominantly affected the antero-middle segment in non-SpA, and were uncommon in the postero-middle segment.

MRI lesions in SpA: a comparison with noninflammatory back pain using propensity score adjustment method

Background:

Magnetic resonance imaging (MRI) is important in the management of axial spondyloarthritis (SpA). However, many MRI lesions are not exclusive to axial SpA. Further characterization of these lesions may lead to better clinical decisions.

Objective:

The objective of this study was to compare the frequency of individual spinal MRI lesions between axial SpA and noninflammatory back pain. The factors associated with individual lesions in participants with axial SpA were also determined.

Design:

This was a cross-sectional observational study.

Methods:

MRI lesions in 447 participants with axial SpA and 122 participants with noninflammatory back pain were compared using the propensity score adjustment method. Individual lesions included discovertebral lesions (DVL), Modic type 1 lesions, DVL without Modic type 1 lesions, facet joint lesions, costovertebral joint lesions, corner inflammatory lesions (CIL), and fatty corner lesions (FCL). The factors associated with the lesions were determined using regression analyses.

Results:

Among participants with axial SpA, 81.9% were HLA-B27-positive, 55.0% had radiographic axial SpA, and 60.5% had radiographic features of spinal damage (mSASSS >2). Almost half (48.6% in axial SpA versus 31.1% in noninflammatory back pain) had inflammatory lesions on spinal MRI. In propensity score matching with noninflammatory back pain, axial SpA had an increased occurrence of DVL without Modic type 1 lesion (OR = 3.43, p = 0.01), costovertebral lesion (OR = 11.89, p = 0.02), number of CIL (B = 1.19, p < 0.001), and number of FCL (B = 3.33, p < 0.001). Similar associations were found in the regression models in the radiographic axial SpA subgroup: DVL without Modic type 1 lesion (OR = 2.46, p = 0.001), costovertebral lesion (OR = 3.86, p < 0.001), number of CIL (B = 1.13, p < 0.001), and FCL (B = 2.29, p < 0.01).

Conclusion:

MRI lesions including DVL without Modic type 1, costovertebral joint lesions, CIL, and FCL were more specific in axial SpA.

Deep Learning Detects 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 changes can mimic axSpA, and early signs may therefore be missed. Deep neural networks could function as assistance for axSpA detection. Purpose To create a deep neural network to detect MRI changes in sacroiliac joints indicative of axSpA. Materials and Methods This retrospective multicenter study included MRI examinations of five cohorts of patients with clinical suspicion of axSpA collected at university and community hospitals between January 2006 and September 2020. Data from four cohorts were used as the training set, and data from one cohort as the external test set. Each MRI examination in the training and test sets was scored by six and seven raters, respectively, for inflammatory changes (bone marrow edema, enthesitis) and structural changes (erosions, sclerosis). A deep learning tool to detect changes indicative of axSpA was developed. First, a neural network to homogenize the images, then a classification network were trained. Performance was evaluated with use of area under the receiver operating characteristic curve (AUC), sensitivity, and specificity. P < .05 was considered indicative of statistically significant difference. Results Overall, 593 patients (mean age, 37 years ± 11 [SD]; 302 women) were studied. Inflammatory and structural changes were found in 197 of 477 patients (41%) and 244 of 477 (51%), respectively, in the training set and 25 of 116 patients (22%) and 26 of 116 (22%) in the test set. The AUCs were 0.94 (95% CI: 0.84, 0.97) for all inflammatory changes, 0.88 (95% CI: 0.80, 0.95) for inflammatory changes fulfilling the Assessment of SpondyloArthritis international Society definition, and 0.89 (95% CI: 0.81, 0.96) for structural changes indicative of axSpA. Sensitivity and specificity on the external test set were 22 of 25 patients (88%) and 65 of 91 patients (71%), respectively, for inflammatory changes and 22 of 26 patients (85%) and 70 of 90 patients (78%) for structural changes. Conclusion Deep neural networks can detect inflammatory or structural changes to the sacroiliac joint indicative of axial spondyloarthritis at MRI. © RSNA, 2022 Online supplemental material is available for this article.

A glance into the future of diagnosis and treatment of spondyloarthritis

The last two decades have seen major developments in the field of spondyloarthritis (SpA), but there are still important unmet needs to address. In the future, we envisage important advances in the diagnosis and treatment of SpA. In the diagnosis of SpA, the use of online and social media tools will increase awareness of the disease and facilitate the referral of patients to rheumatology clinics. In addition, more specific diagnostic tests will be available, especially advanced imaging methods and new biomarkers. This will allow most patients to be diagnosed at an early stage of the disease. In the treatment of SpA, an increasing number of novel treatment targets can be expected, most of which will be directed against intracellular enzymes. We hope to see more strategy trials shaping treatment pathways in SpA and accommodating principals of precision medicine. Approved treatment options will be available for both axial and peripheral SpA. We also hope to intervene not only at the inflammation level but also at the level of underlying immunological processes that might be associated with a higher probability of long-standing remission if not a cure. Finally, artificial intelligence techniques will allow for the analysis of large-scale data to answer relevant research questions for the diagnosis and management of patients with SpA.

Magnetic resonance image compilation sequence to quantitatively detect active sacroiliitis with axial spondyloarthritis

BACKGROUND

To evaluate the diagnostic value of quantitative parameters [T1, T2, and proton density (PD) value] generated from magnetic resonance image compilation (MAGiC) sequence for active sacroiliitis in the patients with axial spondyloarthritis (ax-SpA).

METHODS

A total of 90 consecutive ax-SpA patients were recruited and divided into an active group (n=48) and inactive group (n=42) based on the Spondyloarthritis Research Consortium Canada (SPARCC) score in this prospective study. In addition, 47 healthy volunteers were recruited as the control group. All participants underwent magnetic resonance (MR) scanning (including MAGiC sequence and T2 mapping sequence) to obtain the T1 value, T2 value, PD value of MAGiC sequence (MAGiC T1 value, T2 value, PD value), and the T2 value of T2 mapping sequence (T2 map T2 value). Intraclass correlation coefficients (ICC) were calculated to assess the inter‑ and intra‑observer agreement. The correlation between the MAGiC T2 value and the T2 map T2 value was analyzed using Spearman's Rho. One-way analysis of variance (ANOVA) and receiver operating characteristic (ROC) analysis were performed for all parameters.

RESULTS

For the active group, inactive group, and control group, the MAGiC T1 value, T2 value, PD value, and T2 map T2 value were (1,700.91±725.40, 546.58±59.49, 640.25±95.79 ms), (129.37±23.85, 117.16±20.37, 90.52±12.05 ms), (76.47±15.92, 82.69±9.51, 75.51±9.17 pu), and (96.75±16.06, 87.96±9.27, 82.03±10.17 ms), respectively. The difference of the MAGiC T1 value and the MAGiC T2 value in the three groups was statistically significant (P<0.05). The MAGiC PD value was only statistically significant between inactive and control groups (P=0.001). When comparing the ROC curves of quantitative values among the three groups, MAGiC T1 value showed higher diagnostic efficacy than MAGiC T2 value between the active and inactive groups (MAGiC T1AUC: 0.971, MAGiC T2AUC: 0.655, P<0.0001), and the MAGiC T2 value showed higher diagnostic efficacy than T2 map T2 value between the active group and control group, and the inactive group and control group (MAGiC T2AUC: 0.940, T2 map T2AUC: 0.784, P=0.0021; MAGiC T2AUC: 0.877, T2 map T2AUC: 0.644, P=0.0011). The consistency of measurements was excellent (ICC =0.972-0.998). The MAGiC T2 value was positively correlated with the T2 map T2 value, but with a low correlation (r=0.402; P<0.001).

CONCLUSIONS

A significant difference was detected between the MAGiC T1 and T2 values among the three groups, while MAGiC PD value had limited diagnostic value. MAGiC T1 value was better at differentiating the active group and inactive group than MAGiC T2 value. MAGiC T2 value was better at differentiating the active group and control group, the inactive group and control group than T2 map T2 value.

Extracellular matrix protein turnover markers are associated with axial spondyloarthritis-a comparison with postpartum women and other non-axial spondyloarthritis controls with or without back pain

Background

Axial spondyloarthritis (axSpA) is a common chronic inflammatory disease, associated with extracellular matrix (ECM) remodeling of the cartilage, bone, and connective tissues. The primary symptom of axSpA is back pain, caused by inflammation. However, there is a medical need to truly identify patients with axSpA from other subjects with buttock or low back pain attributable to other reasons. We aimed to investigate circulating biomarkers of ECM/inflammation (MMP-degraded type I (C1M), II (C2M, T2CM), III (C3M), IV (C4M), VI (C6M), and X (C10C, COL10NC) collagens, CRPM, PROM and VICM) and ECM formation of type II (PRO-C2), III (PRO-C3), IV (PRO-C4), and VI (PRO-C6) collagens as potential biomarkers to identify patients with axSpA.

Methods

We measured biomarkers from a cross-sectional study with 204 participants by enzyme-linked immunosorbent assay (ELISA). The study included axSpA patients (N = 41), women with postpartum buttock/pelvic pain (N = 46), disc herniation (N = 25), and a group of healthy subjects (including women without postpartum pelvic pain (N = 14), subjects with various types of physical strain (cleaning staff (N = 26) long-distance runners (N = 23)), and healthy men (N = 29)). Differences between the groups were calculated by ANCOVA and AUC, while Spearman’s correlations were performed with ECM biomarkers and clinical scores.

Results

Patients with axSpA expressed significantly higher levels of C1M, C4M, and VICM (p < 0.05-p < 0.0001) compared to all the non-axSpA control groups. Further, C6M and PRO-C4 were significantly higher in patients with axSpA (both p < 0.0001) compared to women with postpartum pelvic pain and healthy subjects, whereas PRO-C3 was significantly lower compared to healthy subjects (p = 0.01). The best ECM common biomarker to differentiate between axSpA and the non-axSpA control groups was PRO-C4 (AUC ≥ 0.75; specificity ≥ 0.79, sensitivity = 0.65). Mild correlations were observed between collagen turnover and inflammation biomarkers and CRP and MRI (ρ ≥ 0.3; p < 0.05-p < 0.001).

Conclusions

Biomarkers of type I, IV, and VI collagen and biomarkers of inflammation showed an altered turnover in patients with axSpA compared with the non-axSpA control groups. Such biomarkers may be useful in combination with MRI or independently to separate patients with axSpA from other back pain conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02839-1.

Subchondral bone attenuation coefficient utility of the sacroiliac margins to differentiate spondyloarthritis and osteitis condensans ilii

Introduction

Differentiating ankylosing spondylitis (AS) from osteitis condensans ilii (OCI) remains challenging for clinicians. The aim of this study was to determine whether Subchondral Bone Attenuation Coefficient of the SacroIliac margins (SBAC-SI) is different in AS, OCI and diffuse idiopathic skeletal hyperostosis (DISH).

Methods

A monocentric retrospective observational study was performed at the University Hospital of Besançon. Patients included were followed for AS, DISH or OCI and underwent CT scan including sacroiliac joint. Patients with tumour lesion of bone or a history of pelvic radiotherapy were excluded. AS and OCI patients were matched with a control of the same age and sex. SBAC-SI was evaluated by the sum of 24 identical circular regions of interest, 8 per slice (anterior, middle and posterior).

Results

Thirty AS and AS controls, 31 DISH, 29 OCI and OCI controls were included. SBAC-SI score was 9727 (±2430) in the OCI group (p<0.001), 3563 (±1860) in the AS group, 3899 (±1937) in the DISH group, 4224 (±1693) in the AS control group and 5445 (±1205) in the OCI control group. A threshold of 7500 HU had the best discriminative value between OCI and AS (youden index: 0.89). In AS, disease duration is negatively associated with SBAC-SI (r: −0.623; p<0.01) and HLA B27 is associated with lower SBAC-SI (6523 (5198; 7137) vs 2809 (1568; 3371); p<0.001).

Conclusion

SBAC-SI is significatively different between AS and OCI and could help to distinguish these two diseases.

Improving the design of RCTs in non-radiographic axial spondyloarthritis

Concerns have been raised that randomized placebo-controlled trials (RCTs) in non-radiographic axial spondyloarthritis (nr-axSpA) might be failing to identify patients that best show differences in clinical response rates between those receiving active drug and those receiving placebo therapies; in addition, some studies might even be showing spurious differences in responses to TNF and IL-17 inhibitor therapies. In particular, the most recent phase III RCTs in nr-axSpA have reported variable and generally lower response rates than observed in phase III trials of patients with ankylosing spondylitis and in trials conducted a decade ago in patients with early axSpA who were selected on the basis of axial inflammation evident on MRI scans. We argue that these observations at least partly reflect an RCT design that does not take full advantage of MRI to select patients who are responsive to therapy because the current MRI-based inclusion criteria cannot identify patients with axSpA with sufficient specificity. We propose that future studies should be designed using revised patient inclusion criteria based on expanded MRI evaluation and the application of data-driven definitions of a positive MRI for inflammatory and structural lesions typical of axSpA reported in an international multicentre analysis of MRI scans from the Assessment of SpondyloArthritis International Society (ASAS) classification cohort.

Heterogeneity of axial spondyloarthritis: genetics, sex and structural damage matter

OBJECTIVE

Axial spondyloarthritis (axSpA) comprises both radiographic and non-radiographic disease. However, the paucity of specific objective measures for the disease and current classification criteria showing suboptimal specificity contribute to disease heterogeneity observed in clinical practice and research. We used a historical cohort of patients with axSpA to assess sources of heterogeneity.

METHODS

The study involved 363 axSpA probands recruited from membership of the Swiss Ankylosing Spondylitis Patient Society. Participants underwent examination by a rheumatologist, completed questionnaires and provided blood samples for HLA typing. Patients underwent radiography of sacroiliac joints and were categorised according to the New York (NY) criteria (ankylosing spondylitis (AS) or non-radiographic axSpA (nr-axSpA)) and HLA-B27 status. Genetic characterisation by single nucleotide polymorphism microarray was performed and AS polygenic risk scores (PRS) were calculated.

RESULTS

Considerable heterogeneity was observed. The male to female ratio for AS (NY+) was 3:1, but 1:1 for nr-axSpA. For HLA-27(+) AS, the ratio was 2.5:1, but nearly 1:1 for HLA-B27(-) disease. Women with nr-axSpA had strikingly lower mean PRS and lower HLA-B27 prevalence than men with nr-axSpA or NY(+) male and female patients with AS. PRS was able to distinguish male but not female patients with nr-axSpA from related healthy first-degree relatives. Radiographic sacroiliitis was strongly associated with HLA-B27, especially in men.

CONCLUSION

Women clinically diagnosed with axSpA but without radiographic sacroiliitis as a group have a disease that is distinct from AS by the modified New York criteria overall and from nr-axSpA in men. Given the high degree of heterogeneity, stratified or adjusted analysis of effectiveness studies is indicated, taking genetics, sex and radiographic damage (sacroiliitis) into account.

Progressive increase in sacroiliac joint and spinal mri lesions in healthy individuals in relation to age

OBJECTIVES

MRI plays a pivotal role in spondyloarthritis (SpA) diagnosis. However, detailed description of MRI findings of the sacroiliac joints (SIJ) and spine in healthy individuals is currently lacking. We therefore sought to evaluate the occurrence of MRI-SIJ/spine lesions in healthy individuals in relation to age.

METHODS

Ninety-five healthy subjects (20-49 years) underwent MRI-SIJ and -spine. BME and structural lesions of the SIJ were scored using the SPARCC method. Spinal inflammatory and structural lesions were evaluated using the SPARCC MRI spine inflammation index and the CANDEN MRI scoring system, respectively. Fulfillment of the ASAS definition of a positive MRI for sacroiliitis/spondylitis was reviewed. Findings were compared with MRI of axial SpA patients from the Be-GIANT cohort.

RESULTS

17.2% of subjects aged ≥30 fulfilled the definition of a positive MRI for sacroiliitis, but this occurred rarely in younger subjects. SIJ erosions (20.0%) and fat metaplasia (13.7%) were detected across all age groups. Erosions were more frequently visualized in subjects aged ≥40 (39.3%). Spinal BME (35.7%) and fat metaplasia (28.6%) were common in subjects older than 40 years. Nonetheless, only one subject had ≥3 corner inflammatory lesions. SIJ and spinal SPARCC scores and total structural lesions scores increased progressively with age.

CONCLUSION

Contrary to what is commonly believed, structural MRI-SIJ lesions are frequently seen in healthy individuals. Especially in older subjects, the high occurrence of inflammatory and structural MRI lesions impacts their specificity for SpA, which has important implications for the interpretation of MRI in patients with clinical suspicion of SpA.

Nonradiographic axial spondyloarthritis: expanding the spectrum of an old disease: A narrative review

Nonradiographic axial spondyloarthritis (nr-axSpA) represents a distinct phenotype within the spectrum of axial spondyloarthritis (axSpA), which is characterized by a range of clinical manifestations. Despite a high disease burden that is comparable to ankylosing spondylitis (also known as radiographic axSpA), there is an unmet need to recognize and effectively manage patients with active nr-axSpA.A targeted literature search was conducted in OVID (MEDLINE and Embase databases) to identify articles on nr-axSpA, including its definition, demographics, epidemiology, burden, diagnosis, clinical presentation, and treatment guidelines.The lack of adequate epidemiological data and incomplete understanding of nr-axSpA among rheumatologists and nonrheumatologists contributes to delayed referrals and diagnosis. This delay results in a substantial burden on patients, physically and psychologically, and the healthcare system. Targeted therapies, such as biologics, including inhibitors of tumor necrosis factor or interleukin-17A, have been approved and utilized for the management of nr-axSpA, and other novel therapeutics with different mechanisms of action are in development. Raising awareness among US internists regarding the prevalence of nr-axSpA, disease burden, clinical presentation, diagnostic tools, and available treatments is important for improved disease management.Future clinical investigations focusing on the development of markers that aid early diagnosis and predict treatment response may also improve the management of nr-axSpA. This review provides an overview of nr-axSpA with the aim of raising awareness of the disease among US internists, with an overarching goal to contribute toward the improved recognition and timely referral of these patients to rheumatologists for diagnosis and management.

Prevalence of sacroiliitis among patients referred for hip MR arthrography

OBJECTIVE

To determine the prevalence of sacroiliitis among patients who have been referred for MR arthrography.

MATERIALS AND METHODS

A retrospective search identified 130 consecutive MR arthrograms of the hip performed on a 1.5T Siemens Avanto at our institution from August 2013 to August 2014. Four studies were excluded due to the absence of a coronal short tau inversion recovery sequence of the pelvis, leaving 126 studies for analysis. A musculoskeletal radiology fellow and three attending musculoskeletal radiologists reviewed the images for the presence of bone marrow edema affecting the sacroiliac joints. Only cases of bone marrow edema meeting the Assessment of SpondyloArthritis international Society definition were considered positive. The two-tailed Fisher's exact test was used to compare the prevalence of positive MRI findings among age and gender groups. GraphPad InStat (GraphPad Software) was used for statistical calculations.

RESULTS

Patients less than 40 years of age demonstrated a statistically higher prevalence of positive MRI findings of sacroiliitis when compared to patients older than 40 (p = 0.0082). No difference in prevalence was found between genders. Overall prevalence of MRI signal alteration suggestive of sacroiliitis as defined by the Assessment of SpondyloArthritis international Society was 4.8%. Among the six patients with positive findings, two were subsequently diagnosed with spondyloarthritis.

CONCLUSION

Hip pain may be a presenting symptom of spondyloarthritis and attention should be paid to the sacroiliac joints during screening examinations, particularly in patients less than 40 years of age.

[Low back pain from a rheumatological point of view]

Low back pain is the leading symptom of a family of inflammatory rheumatic diseases grouped under the umbrella term "spondyloarthritides". This paper discusses the main clinical, laboratory, and imaging features of spondyloarthritides in the diagnostic context of low back pain. It also highlights the current therapeutic principles of axial spondyloarthritis.

Differences in topographical location of sacroiliac joint MRI lesions in patients with early axial spondyloarthritis and mechanical back pain

Background

Early diagnostics of axial spondyloarthritis (axSpA) remains a challenge. Traditional imaging one-plane sacroiliac joint (SIJ) MRI assessment is used. By introducing a two-plane assessment system, the objective was to analyse the differences in SIJ MRI changes in early axSpA compared with changes in patients with mechanical back pain (MBP) by exploring the differences in volume and location.

Methods

MRIs in the early diagnostic state of 25 axSpA patients (mean age 31.3 years) and 59 MBP patients (mean age 32.3 years) were included. The MRIs were assessed by two readers regarding the distribution of bone marrow edema (BME) in 14 joint portions and structural changes in six joint portions in addition to SIJ anatomical variations and lumbar spine disc degeneration.

Results

AxSpA patients had a significantly higher overall BME sumscore (volume) of 25.1 compared to MBP patients 6.8, p < 0.005. The MBP group had the highest prevalence (66%) and sumscore (5.7) in the middle anterior sacrum. The axSpA group had significantly higher prevalence and sumscores in all joint portions except the three cartilaginous anterior sacral joint portions, including the ligamentous compartments (prevalence 40–60% compared to 8–15%, p both < 0.005). The axSpA group had also a significantly higher prevalence of erosions and fatty marrow disposition, but there were no differences in the prevalence of anatomical variations except the bipartite iliac bony plate.

Conclusions

AxSpA patients demonstrated a widespread distribution of both inflammatory and structural changes, including high BME occurrence in the ligamentous joint portions whereas patients with MBP had the highest occurrence of BME in the middle anterior sacrum. These findings may help differentiate axSpA patients from other back pain conditions in the early diagnostic phase.

Anatomical variation at the sacroiliac joints in young adults: estimated prevalence by CT and concomitant diagnostics by MRI

OBJECTIVE

To estimate the prevalence of atypical anatomical morphologies at the sacroiliac joints (SIJ) in young adults by CT and analyze the diagnostic ability of MRI to detect the variations in addition to concomitant MRI findings that could be misdiagnosed as inflammatory changes.

MATERIALS AND METHODS

The study sample constituted CT examinations of 155 individuals aged 18-40 years and prospectively collected comparative SIJ MRI examinations of 49, who also filled out a questionnaire on back and buttock pain. The CT and MRIs were analyzed by two musculoskeletal radiologists regarding seven SIJ variations and additional subchondral bone marrow edema (BME) by MRI.

RESULTS

CT and MRI interobserver agreements were good or very good for most variations. Mean age of the 155 individuals was 28 years, 99 (64%) were males; 88 (57%) had at least one SIJ variation, and most frequent were dysmorphic cartilaginous joint facets (n = 33, 21%), bipartite iliac bony plate (n = 27, 17%), accessory SIJ (n = 24, 16%), and iliosacral complex (n = 18, 12%), with a female predominance of all variations. The ability of MRI to detect the frequent variations was satisfying. Dysmorphic cartilaginous joint facets, accessory SIJ, and iliosacral complex were frequently observed in individuals reporting symptoms and were accompanied by BME, often located anteriorly in sacrum/inferiorly in ilium.

CONCLUSION

Atypical SIJ morphology is frequent in young adults, especially females, demanding further research into the anatomical natural variation. Most of the variations were detectable by MRI and three variations warrant further exploration as they often were accompanied by symptoms and/or BME.

Current differentiation between radiographic and non-radiographic axial spondyloarthritis is of limited benefit for prediction of important clinical outcomes: data from a large, prospective, observational cohort

OBJECTIVE

To compare disease characteristics and outcomes between patients with axial spondyloarthritis with non-radiographic disease (nr-axSpA), bilateral grade 2 sacroiliitis (r22axSpA) and unilateral/bilateral grade 3-4 sacroiliitis (r3+axSpA) according to the modified New York criteria.

METHODS

We included patients with axial spondyloarthritis with available pelvic radiographs from the Swiss Clinical Quality Management Cohort. Retention of a first tumour necrosis factor inhibitor (TNFi) was investigated with multiple adjusted Cox proportional hazards models. The proportion of patients reaching 50% reduction in the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI50) at 1 year was assessed with multiple adjusted logistic regression analyses. Spinal radiographic progression, defined as an increase in ≥2 mSASSS units in 2 years, was assessed in generalised estimating equation models.

RESULTS

From 2080 patients, those with nr-axSpA (n=485) and r22axSpA (n=443) presented with lower C reactive protein levels and less severe clinical spinal involvement compared with patients with r3+axSpA (n=1152). While TNFi retention was similar in r22axSpA and nr-axSpA, the risk of discontinuation was significantly lower in r3+axSpA (HR 0.60, 95% CI 0.44 to 0.82 vs nr-axSpA). BASDAI50 responses at 1 year were comparable in r22axSpA and nr-axSpA, with a better response associated with r3+axSpA (OR 2.05, 95% CI 1.09 to 3.91 vs nr-axSpA). Spinal radiographic progression was similar in r22axSpA and nr-axSpA and significantly higher in r3 +axSpA.

CONCLUSION

Patients with r22axSpA are comparable to nr-axSpA patients but differ from patients with more severe sacroiliac damage with regard to treatment effectiveness and spinal radiographic progression. Therefore, current differentiation between nr-axSpA and radiographic disease seems of limited use for outcome prediction.

The association between elevated serum interleukin-22 and the clinical diagnosis of axial spondyloarthritis: A retrospective study

OBJECTIVE

There is an unmet need for a reliable biomarker for the differentiation of axial spondyloarthritis (AxSpA) from its mimickers. Serum levels of interleukin-22 (IL-22) have previously been found to be significantly elevated in patients with AxSpA compared with healthy individuals or persons with osteoarthritis.

METHODS

Consecutive patients with established or suspected AxSpA were enrolled. The clinical data, as well as results of laboratory and imaging studies, were acquired from patients' charts. The final diagnosis of definite or probable SpA, or an alternative diagnosis, was determined, and the serum levels of IL-22 were examined by enzyme-linked immunosorbent immunoassay.

RESULTS

Interleukin-22 levels were significantly higher in patients with definite AxSpA (29 patients) compared with patients with alternative diagnoses (14 patients) and healthy volunteers (16 individuals; P < 0.001 for both comparisons). The sensitivity and specificity of the serum IL-22 for the AxSpA diagnosis were 0.68 (95% CI 0.49-0.84) and 0.86 (95% CI 0.68-0.95), respectively, for the cut-off value of 5 pg/mL. In patients with AxSpA, serum IL-22 levels did not correlate with modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Ankylosing Spondylitis Disease Activity Score (ASDAS), or serum C-reactive protein.

CONCLUSION

Serum IL-22 levels are elevated in patients with the clinical diagnosis of AxSpA and can potentially serve as an independent biomarker for the differentiation of AxSpA from its non-inflammatory mimickers.

MRI in axial spondyloarthritis: understanding an 'ASAS-positive MRI' and the ASAS classification criteria

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.

Australian Consensus Statements for the Assessment and Management of Non-radiographic Axial Spondyloarthritis

Background

The understanding of non-radiographic axial spondyloarthritis (nr-axSpA) has accelerated over the last decade, producing a number of practice-changing developments. Diagnosis is challenging. No diagnostic criteria exist, no single finding is diagnostic, and other causes of back pain may act as confounders.

Aim

To update and expand the 2014 consensus statement on the investigation and management of non‐radiographic axial spondyloarthritis (nr-axSpA).

Methods

We created search questions based on our previous statements and four new topics then searched the MEDLINE and Cochrane databases. We assessed relevant publications by full-text review and rated their level of evidence using the GRADE system. We compiled a GRADE evidence summary then produced and voted on consensus statements.

Results

We identified 5145 relevant publications, full-text reviewed 504, and included 176 in the evidence summary. We developed and voted on 22 consensus statements. All had high agreement. Diagnosis of nr-axSpA should be made by experienced clinicians, considering clinical features of spondyloarthritis, blood tests, and imaging. History and examination should also assess alternative causes of back pain and related conditions including non-specific back pain and fibromyalgia. Initial investigations should include CRP, HLA-B27, and AP pelvic radiography. Further imaging by T1 and STIR MRI of the sacroiliac joints is useful if radiography does not show definite changes. MRI provides moderate-to-high sensitivity and high specificity for nr-axSpA. Acute signs of sacroiliitis on MRI are not specific and have been observed in the absence of spondyloarthritis. Initial management should involve NSAIDs and a regular exercise program, while TNF and IL-17 inhibitors can be used for high disease activity unresponsive to these interventions. Goals of treatment include improving the frequent impairment of social and occupational function that occurs in nr-axSpA.

Conclusions

We provide 22 evidence-based consensus statements to provide practical guidance in the assessment and management of nr-axSpA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40744-021-00416-7.

Magnetic resonance imaging findings in the normal pediatric sacroiliac joint space that can simulate disease

BACKGROUND

Magnetic resonance imaging (MRI) features of active sacroiliac joint inflammation include joint space fluid and enhancement, but it is unclear to what extent these are present in normal children.

OBJECTIVE

To describe normal MRI appearances of pediatric sacroiliac joint spaces in boys and girls of varying ages.

MATERIALS AND METHODS

In this ethics-approved prospective study, 251 children (119 boys, 132 girls; mean age: 12.4 years, range: 6.1-18.0 years), had both oblique-coronal T1-weighted and short tau inversion recovery (STIR) sacroiliac joint MRI. Of these, 127 were imaged for other reasons and had asymptomatic sacroiliac joints ("normal cohort") while 124 had low back pain with no features of sacroiliitis on initial clinical MRI review ("low-back-pain cohort"). Post-gadolinium T1-weighted sequences were available in 16/127 normal and 124/124 low-back-pain subjects. Three experienced radiologists scored high signal in the sacroiliac joint space on STIR (score 0=absent; 1=high signal compared to normal bone marrow present anywhere in the joint but not as bright as fluid [compared to vessels, cerebrospinal fluid]; 2=definite fluid signal in part of the joint; 3=definite fluid signal, entire vertical height, majority of slices) and, when available, joint space post-contrast enhancement (0=no high signal/enhancement; 1=thin, symmetrical, mildly increased linear high signal present in the joint space; 2=focal, thick or intense enhancement). Associations between joint signal scores, age, gender and sacral apophyseal closure were analysed.

RESULTS

Increased signal on STIR (score 1-3) was present in 74.7% of pediatric sacroiliac joint spaces, as intense as fluid in 18.4%. There was no significant difference in proportion by gender, side or cohort, but girls showed peak signal earlier than boys (10 years old vs. 12 years old, respectively). On post-gadolinium T1-weighted sequences, a thin rim of increased signal was nearly universally seen in sacroiliac joint spaces without focal, intense or thick post-contrast enhancement.

CONCLUSION

Sacroiliac joint spaces of most children demonstrate mildly increased signal on STIR, compared to normal bone marrow, and thin rim-like enhancement on post-contrast T1 images, likely related to cartilage. These findings should not be confused with sacroiliitis.