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

Anatomical variation of the sacroiliac joints - what the rheumatologist should know

PURPOSE OF REVIEW

Anatomical variations of the sacroiliac joints (SIJ) pose challenges in the diagnosis of axial spondyloarthritis (axSpA). Increased reliance on magnetic resonance imaging (MRI) for early detection has led to concerns about specificity, as anatomical variants can mimic inflammatory changes. This review highlights common SIJ variations and their implications for rheumatologists interpreting imaging findings.

RECENT FINDINGS

Recent studies emphasize the high prevalence of SIJ anatomical variations, particularly in females, and their potential to influence imaging interpretation. Variations such as crescent-shaped ileum, intraarticular dysmorphisms, and accessory joint facets can lead to bone marrow edema and sclerosis, mimicking sacroiliitis. Additionally, lumbosacral transitional vertebrae alter SIJ biomechanics, potentially exacerbating symptoms in axSpA patients. Advances in MRI and computed tomography (CT) imaging protocols provide improved differentiation between anatomical variants and true inflammatory changes.

SUMMARY

Recognizing SIJ anatomical variations is crucial for avoiding misinterpretation of imaging findings and overdiagnosis of axSpA. MRI protocols incorporating additional imaging planes and CT correlation can enhance diagnostic accuracy. Awareness of these variations can refine patient management strategies, ensuring appropriate treatment for inflammatory and biomechanical SIJ pathologies.

Sacroiliac joint dysfunction: anatomy, pathophysiology, differential diagnosis, and treatment approaches

The sacroiliac joints (SIJ) play a pivotal role in pelvic stability and load transmission. SIJ-related disorders can pose a diagnostic challenge because of complex anatomy, non-specific imaging findings, and overlapping symptomatology with other lower back conditions. Broadly, SIJ pathology can be divided into the following categories: infectious, inflammatory, degenerative, mechanical, traumatic, and neoplastic. On the spectrum of mechanical disorders is the entity of SIJ dysfunction, defined as pain localized to the SIJ due to non-inflammatory causes. This paper aims to enhance the understanding of SIJ dysfunction by exploring SIJ anatomy, pathophysiology, and differential diagnosis for SIJ pain. Etiologies, associations, and diagnostic physical examination maneuvers for SIJ dysfunction are reviewed. We will discuss the role of diagnostic imaging in SIJ dysfunction and propose imaging findings which may indicate the diagnosis. Finally, we will discuss therapeutic strategies to treat SIJ dysfunction. By delving into the complexities of SIJ anatomy and pathophysiology, this paper provides valuable discernment for the diagnosis and management of SIJ-related disorders.

Impact of combining magnetic resonance images and radiographs on radiographic grading of sacroiliitis and classification in axial spondyloarthritis: a reliability study

To investigate the reliability of sacroiliac radiographic grading based on the modified New York criteria, both through grading pelvic radiographs alone and in combination with sacroiliac magnetic resonance imaging and the influence of alone and multimodal interpretation on the categorization of radiographic and non-radiographic axial spondyloarthritis (r-axSpA and nr-axSpA). Radiographs of the SI joints from patients with axSpA were graded by two rheumatologists independently in two sessions (radiographs only and MRI + radiographs) and followed by consensus sessions with the participation of a radiologist. Overall, anteroposterior pelvic radiographs and T1 weighted MR scans of the sacroiliac joints from 138 patients with axSpA were eligible. Intra- and inter-reader reliability was fair to moderate for both techniques regardless of whether they were examined alone or in conjunction with MRI, however confidence levels of readers were relatively higher in the MRI + radiographs combined technique compared to radiographs only. Regarding the classification, both readers' intra and inter reader agreements were moderate to substantial. The kappa values and agreement were notably higher for the combined reading technique. In the consensus sessions, 10.2% of patients were recategorized. Merging the information from MRI scans with pelvic radiographs yielded no notable enhancement in the accuracy of radiographic grading of SI joint. Categorizing axSpA as either radiographic or non-radiographic based on pelvic radiography falls short in reliability even after combining with MR images and may likely call for a more reliable definition, axSpA with or without structural changes, relying on more advanced imaging techniques than radiographs.

The imaging crisis in axial spondyloarthritis

Imaging holds a pivotal yet contentious role in the early diagnosis of axial spondyloarthritis. Although MRI has enhanced our ability to detect early inflammatory changes, particularly bone marrow oedema in the sacroiliac joints, the poor specificity of this finding introduces a substantial risk of overdiagnosis. The well intentioned push by rheumatologists towards earlier intervention could inadvertently lead to the misclassification of mechanical or degenerative conditions (eg, osteitis condensans ilii) as inflammatory disease, especially in the absence of structural lesions. Diagnostic uncertainty is further fuelled by anatomical variability, sex differences, and suboptimal imaging protocols. Current strategies-such as quantifying bone marrow oedema and analysing its distribution patterns, and integrating clinical and laboratory data-offer partial guidance for avoiding overdiagnosis but fall short of resolving the core diagnostic dilemma. Emerging imaging technologies, including high-resolution sequences, quantitative MRI, radiomics, and artificial intelligence, could improve diagnostic precision, but these tools remain exploratory. This Viewpoint underscores the need for a shift in imaging approaches, recognising that although timely diagnosis and treatment is essential to prevent long-term structural damage, robust and reliable imaging criteria are also needed. Without such advances, the imaging field risks repeating past missteps seen in other rheumatological conditions.

Current and future role of CT and advanced CT applications in inflammatory arthritis in the clinic and trials

Computed tomography (CT) has traditionally been underutilized in the imaging of inflammatory arthritis due to its limitations in assessing soft tissue inflammation and concerns over radiation exposure. However, recent technological advancements have positioned CT as a more viable imaging modality for arthritis, offering high specificity and sensitivity in detecting structural bone changes. However, advances in ultra-low-dose CT protocols and AI-driven image reconstruction have significantly reduced radiation exposure while maintaining diagnostic quality. Dynamic CT and spectral CT techniques, including dual-energy CT (DECT), have broadened CT's application in assessing dynamic joint instabilities and visualizing inflammatory changes through material-specific imaging. Techniques such as CT subtraction imaging and iodine mapping have enhanced the detection of active soft-tissue inflammation, virtual non-calcium reconstructions, and the detection of bone marrow edema. Possible CT applications span various forms of arthritis, including gout, calcium pyrophosphate deposition disease (CPPD), psoriatic arthritis, and axial spondyloarthritis. Beyond its diagnostic capabilities, CT's ability to provide detailed structural assessment positions is a valuable tool for monitoring disease progression and therapeutic response, particularly in clinical trials. While MRI remains superior for soft tissue evaluation, CT's specificity for bone-related changes and its potential for integration into routine arthritis management warrant further exploration and research. This review explores the current and emerging roles of CT in arthritis diagnostics, with a focus on novel applications and future potential.

Sacroiliac Joint: Mimics and Pitfalls

Sacroiliac joint pathology presents a complex diagnostic challenge due to the diverse range of conditions, both mechanical and inflammatory, that can affect the joint. Although axial spondyloarthritis-related sacroiliitis is often the most recognized pathology, numerous other conditions closely mimic axial spondyloarthritis in both clinical presentation and imaging features. This review describes key anatomical aspects of the sacroiliac joint, including its distinct morphology, ligamentous support, and histologic characteristics, essential for understanding and differentiating various pathologies. It also examines detailed imaging findings from magnetic resonance imaging, computed tomography, and radiography in relation to each pathologic condition. By providing a framework for distinguishing between common and rare sacroiliac joint disorders and axial spondyloarthritis, this article will enhance diagnostic accuracy and offer insights into the anatomical nuances that impact clinical and imaging assessments.

Whole-body Magnetic Resonance Imaging in Inflammatory Spine and Joint Disease

Whole-body magnetic resonance imaging (WB-MRI) can effectively diagnose rheumatologic diseases with systemic and multifocal characteristics, such as spondyloarthritis, chronic recurrent multifocal osteomyelitis, and synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome, among others. Advances in rheumatic disease treatments have emphasized the importance of early diagnosis for effective management, function preservation, and improved quality of life. WB-MRI offers comprehensive imaging of the musculoskeletal system, detecting early and subtle disease changes that traditional methods might overlook. Initially used for spondyloarthritis, the technique has recently expanded to other rheumatic diseases and is becoming the gold standard for diagnosing and monitoring chronic nonbacterial osteomyelitis in pediatric patients. This review article presents the current status of WB-MRI in rheumatologic conditions.

Zero Echo Time and Similar Techniques for Structural Changes in the Sacroiliac Joints

Spondyloarthritis (SpA) encompasses inflammatory disorders affecting the axial skeleton, with sacroiliitis as a hallmark feature of axial SpA (axSpA). Imaging plays a vital role in early diagnosis and disease monitoring. Magnetic resonance imaging (MRI) is the preferred modality for detecting early inflammatory changes in axSpA, whereas structural lesions are better visualized using computed tomography (CT). However, synthetic computed tomography (sCT), a technique that generates CT-like images from MRI data, including deep learning methods, zero echo time, ultrashort echo time, and gradient-recalled echo sequences, has emerged as an innovative tool. It offers detailed anatomical resolution without ionizing radiation and combines the advantages of both, MRI and CT, by enabling the simultaneous evaluation of inflammatory and structural lesions. This review explores the potential role of MRI-based sCT in assessing structural changes in the sacroiliac joints, particularly in the context of axSpA, discussing conventional imaging and highlighting the potential of sCT to enhance early detection and monitoring of sacroiliitis.

Spondyloarthritis endgame: MRI versus BoneMRI in sacroiliitis

The Assessment in SpondyloArthritis International Society (ASAS) classification criteria characterize sacroiliitis by active inflammation and structural lesions. Detection of lesions such as bone marrow edema, joint surface erosions and ankylosis is important, because progressing treatment options benefit from early diagnosis and detailed treatment response monitoring. Recent technological advancements have made various imaging modalities available to assess these findings, i.e., various sorts of CT (low dose, dual energy, etc.), MRI and BoneMRI. BoneMRI is an advanced technique where CT-like images are reconstructed from a dedicated MRI sequence, opening opportunities to better characterize structural lesions than on a classic MRI study. The scope of this review is to provide an overview of the pros and cons of MRI and BoneMRI in sacroiliitis and demonstrate the inherent added value of BoneMRI towards state-of-the-art routine MRI sequences.

Pearls and pitfalls in imaging of axial spondyloarthritis for rheumatologists

This review provides key insights into sacroiliitis imaging, covering anatomy, imaging techniques, and interpretation. It focuses on normal physiological changes in young to middle-aged women, children, and the elderly that can resemble sacroiliitis. We emphasize the importance of distinguishing between active and structural lesions, as highlighted in the recent ASAS-SPARTAN standardized magnetic resonance imaging protocol. Physicians should be aware that bone marrow oedema signals on magnetic resonance imaging, a hallmark of active inflammation in axial spondyloarthritis, can also be observed in young to middle-aged women, especially postpartum, even without spondyloarthritis. Paediatric sacroiliac joints may show changes mimicking inflammation due to ongoing bone growth. Furthermore, degenerative changes in the sacroiliac joint are common with advancing age and can be mistaken for sacroiliitis or interpreted as structural changes. The presence of accessory sacroiliac joints, prone to degeneration, further complicates diagnosis. Accurate interpretation requires considering these normal variations to avoid misdiagnosing spondyloarthritis. Collaboration between clinicians and radiologists is crucial, especially when encountering atypical or clinically inconsistent findings.

Diagnostic features of osteitis condensans ilii by MRI-a systematic literature review

OBJECTIVE

To describe and  evaluate the current knowledge of MRI characteristics of osteitis condensans ilii (OCI) in the diagnostics and differentiation of OCI from other conditions.

MATERIALS AND METHODS

The databases PubMed, EMBASE, Scopus, and Web of Science were searched from their inception to March 2024 using the search terms "Magnetic Resonance Imaging" (MESH term in PubMed) and "osteitis condensans ilii" and limited to English language. Two reviewers independently screened titles, abstracts, and full-text eligibility and assessed the risk of bias according to Quality Assessment of Diagnostic Accuracy Studies, QUADAS-2.

RESULTS

The search identified 53 records. Case reports, letters/notes, and conference abstracts were excluded, resulting in 24 reports assessed by full-text, 9 research articles, 14 reviews, and a book chapter. Five retrospective research studies were found eligible for the review. Detailed MRI features of OCI were only described in two studies of patients with pain where they encompassed manifest subchondral iliac sclerosis often accompanied by bone marrow edema (BME) located peripheral to the sclerosis and displaying a continuous distribution and frequently accompanied by sacral BME. Erosions were rare and ankylosis did not occur. Fat deposition in the bone marrow was frequent and similar to BME often located to anterior strain-related joint areas. The QUADAS-2 assessments revealed risks of bias in all studies analyzed, especially regarding general applicability of the MRI features.

CONCLUSION

There is a lack of valid data describing characteristic MRI features in general groups of OCI patients with and without pain.

T2* cartilage mapping in early axial spondyloarthritis: diagnostic accuracy and correlation with clinical characteristics, sacroiliitis MRI scorings, and diffusion metrics

PURPOSE

To determine the performance of T2* cartilage mapping in diagnosing and assessing disease activity in early axial spondyloarthritis (axSpA), and to investigate the interaction of cartilage damage with clinical characteristics, sacroiliitis MRI scorings, and diffusion metrics.

MATERIALS AND METHODS

This prospective study included 83 axSpA patients and 37 no-axSpA patients. Clinical characteristics, the Assessment of SpondyloArthritis International Society-defined active sacroiliitis on MRI, and T2* SIJs values were recorded. In axSpA, disease activity was evaluated using the ankylosing spondylitis disease activity score-C-reactive protein; active sacroiliitis was evaluated using Spondyloarthritis Research Consortium of Canada, intravoxel incoherent motion, and diffusion kurtosis imaging; chronic sacroiliitis was assessed using composite structural damage score (CSDS) and structural score fat. Mann-Whitney U-test, Kruskal-Wallis test with false discovery rate (FDR), ROC curve, and linear regression were used for statistical analysis.

RESULTS

AxSpA patients had significantly higher T2*SIJs values than no-axSpA patients. (22.86 ± 2.42 ms vs 20.36 ± 1.30 ms, p < 0.001). The combination of T2*SIJs values and active sacroiliitis on MRI had the highest AUC for identifying axSpA. T2*SIJs values were significantly different between the inactive and very high, moderate and very high, high and very high, as well as inactive and high disease activity groups (all pFDR < 0.05). Dk (β = 0.48) and CSDS (β = 0.48) were independently associated with T2*SIJs values.

CONCLUSION

T2* values may be a promising biomarker for diagnosing and differentiating disease activity in early axSpA. Both acute and chronic sacroiliitis influence cartilage properties.

CLINICAL RELEVANCE STATEMENT

Sacroiliac joint cartilage abnormalities can be quantified with T2* relaxation time and allow better characterization of early axSpA.

KEY POINTS

T2* mapping may have value in evaluating axSpA. The combination of T2* values and active sacroiliitis on MRI enhances diagnostic performance for axSpA. Abnormalities measured with T2* values correlate with disease activity, acute sacroiliitis, and degree of structural damage.

The 'Tree trunk and root' model: key imaging findings may anatomically differentiate axial psoriatic arthritis and DISH from axial spondyloarthropathy

Variable axial skeleton inflammation and axial skeleton tissue remodelling with aberrant ligamentous soft-tissue ossification occurs across the axial spondyloarthritis (ax-SpA) axial psoriatic arthritis (ax-PsA) and the diffuse idiopathic skeletal hyperostosis (DISH) spectrum. In this article, we show how imaging has resulted in an enthesis-centric model for different disease pathology compartmentalisation or a 'root and trunk' model for pathological process development. Whilst ankylosing spondylitis is predominantly characterised by early entheseal bony anchorage-related osteitis (root inflammation) and DISH is characterised by ligamentous soft-tissue ossification, ax-PsA is more heterogenous. Whilst ax-PsA may share an identical osteitis pattern to ax-SpA, a substantial proportion of ax-PsA cases have a soft tissue or tree trunk pathology that manifests as back pain with lack of osteitis but prominent ligamentous trunk ossification at later stages. We illustrate this using different imaging modalities to create a base for imaging research to elucidate this pattern of pathology.

Performance analysis of a deep-learning algorithm to detect the presence of inflammation in MRI of sacroiliac joints in patients with axial spondyloarthritis

OBJECTIVES

To assess the ability of a previously trained deep-learning algorithm to identify the presence of inflammation on MRI of sacroiliac joints (SIJ) in a large external validation set of patients with axial spondyloarthritis (axSpA).

METHODS

Baseline SIJ MRI scans were collected from two prospective randomised controlled trials in patients with non-radiographic (nr-) and radiographic (r-) axSpA (RAPID-axSpA: NCT01087762 and C-OPTIMISE: NCT02505542) and were centrally evaluated by two expert readers (and adjudicator in case of disagreement) for the presence of inflammation by the 2009 Assessment of SpondyloArthritis International Society (ASAS) definition. Scans were processed by the deep-learning algorithm, blinded to clinical information and central expert readings.

RESULTS

Pooling the patients from RAPID-axSpA (n=152) and C-OPTIMISE (n=579) yielded a validation set of 731 patients (mean age: 34.2 years, SD: 8.6; 505/731 (69.1%) male), of which 326/731 (44.6%) had nr-axSpA and 436/731 (59.6%) had inflammation on MRI per central readings. Scans were obtained from over 30 scanners from 5 manufacturers across over 100 clinical sites. Comparing the trained algorithm with the human central readings yielded a sensitivity of 70% (95% CI 66% to 73%), specificity of 81% (95% CI 78% to 84%), positive predictive value of 84% (95% CI 82% to 87%), negative predictive value of 64% (95% CI 61% to 68%), Cohen's kappa of 0.49 (95% CI 0.43 to 0.55) and absolute agreement of 74% (95% CI 72% to 77%).

CONCLUSION

The algorithm enabled acceptable detection of inflammation according to the 2009 ASAS MRI definition in a large external validation cohort.

Spine and Sacroiliac Joint Involvement in Newly Diagnosed Patients With Inflammatory Bowel Disease: Clinical and MRI Findings From a Population-Based Cohort

INTRODUCTION

In patients with inflammatory bowel disease (IBD), co-occurring spondyloarthritis (SpA) leads to poorer outcomes and impaired quality of life, highlighting the importance of early detection and effective treatment. This is the first study to assess the prevalence and distribution of axial symptoms and magnetic resonance imaging (MRI)-detected involvement of the spine and sacroiliac joints (SIJs) in early IBD.

METHODS

Newly diagnosed patients with IBD from a prospective, population-based cohort were consecutively recruited. Rheumatological interview, clinical, ultrasound, and MRI assessment for SIJ and spine inflammatory and structural lesions were made using validated scoring methods and consensus definitions of axial SpA (axSpA).

RESULTS

Of 110 patients (ulcerative colitis: 70, Crohn's disease: 40, mean age of 42 years, and 40% male), 48 (44.9%) reported back and/or buttock pain, and 10 (9.1%) had inflammatory back pain. Seventeen (16.7%) patients had MRI findings indicative of axSpA; only 10 of these patients had axial symptoms. Inflammatory MRI lesions were present in SIJs and the spine of 27 (26.5%) and 30 (30.3%) patients, respectively. The Assessment of SpondyloArthritis International Society classification criteria for axSpA were met in 11 (10%) cases. MRI findings typical of axSpA were associated with peripheral joint and entheseal inflammation detected by ultrasound ( P = 0.04). No differences in clinical or imaging findings were found between patients with ulcerative colitis and Crohn's disease.

DISCUSSION

One-in-6 newly diagnosed patients with IBD had MRI findings indicative of axSpA. As 40% of these patients were asymptomatic, this suggests that axSpA is underdiagnosed in early IBD. Multidisciplinary collaboration is essential to ensure early detection of axial inflammation and to enable optimal therapy preventing future structural damage and disability.

Review of the updated definitions and concepts of spinal lesions in axial spondyloarthritis

Spinal imaging may support the diagnosis of axial spondyloarthritis when typical findings are recognized in an appropriate clinical context and it can also indicate disease activity. In May 2022, the definitions for inflammatory and structural spinal lesions in axial spondyloarthritis were updated and validated by the Assessment of SpondyloArthritis international Society (ASAS) magnetic resonance imaging (MRI) working group. The aims of this paper are to demonstrate and describe imaging findings of the spine in patients with axial SpA, including the latest updated definitions by the ASAS, and to show complications in patients with long-standing disease.

Incidental findings on MRI for the evaluation of endometriosis: prevalence and clinical significance

Objectives

This study aimed to analyze the prevalence and clinical significance of incidental findings on MRI for endometriosis. Differences between patients with and without evidence of deep infiltrating endometriosis on MRI were to be examined.

Methods

This was a retrospective, descriptive cross-sectional single-center study. All patients who received a pelvic MRI for endometriosis between April 2021 and February 2023 were included. The presence and frequency of incidental findings were noted after review of all MR images and radiology reports. The potential clinical significance of the findings was analyzed. Differences in the frequency of incidental findings between patients with and without evidence of deep infiltrating endometriosis on MRI were evaluated, utilizing the Chi-square test, Fisher's exact test and Mann-Whitney U-test.

Results

303 consecutive patients (mean age, 33.4 years ± 8.3) were evaluated. Incidental findings were noted in 299/303 (98.7%) patients. Most frequently, ossification of the hip acetabular rim and degenerative changes of the lumbar spine were noted. In 25/303 (8.3%) patients, incidental findings had high clinical significance. For specific incidental findings, significantly higher prevalences were found in patients with than in patients without evidence of deep infiltrating endometriosis on MRI (hip acetabular rim ossification, p = 0.041; annulus fibrosus fissures, p = 0.006; gallstones, p = 0.042).

Conclusions

Incidental findings are very common on pelvic MRI for endometriosis. The detection of incidental findings can lead to the diagnosis of relevant diseases and thus enable early treatment. On the other hand, many incidental findings have no, only minor, or uncertain consequences.

Imaging mimickers of MSK infection

Along with clinical and laboratory findings, imaging has a significant role in the initial evaluation and treatment follow-up of a wide variety of infectious and non-infectious musculoskeletal (MSK) conditions. The imaging findings of many non-infectious MSK processes, such as inflammatory, metabolic, and degenerative arthropathies, complications of diabetes mellitus, osseous and soft tissue injuries, osteonecrosis, tumors, and tumor-like lesions may be nonspecific and often overlap with those found in MSK infections. In this article, the authors discuss the imaging findings of both frequent and rare mimickers of MSK infections, including potential distinguishing characteristics.

ESR Essentials: Imaging of sacroiliitis-practice recommendations by ESSR

Sacroiliitis is commonly seen in patients with axial spondyloarthritis, in whom timely diagnosis and treatment are crucial to prevent irreversible structural damage. Imaging has a prominent place in the diagnostic process and several new imaging techniques have been examined for this purpose. We present a summary of updated evidence-based practice recommendations for imaging of sacroiliitis. MRI remains the imaging modality of choice for patients with suspected sacroiliitis, using at least four sequences: coronal oblique T1-weighted and fluid-sensitive sequences, a perpendicular axial oblique sequence, and a sequence for optimal evaluation of the bone-cartilage interface. Both active inflammatory and structural lesions should be described in the report, indicating location and extent. Radiography and CT, especially low-dose CT, are reasonable alternatives when MRI is unavailable, as patients are often young. This is particularly true to evaluate structural lesions, at which CT excels. Dual-energy CT with virtual non-calcium images can be used to depict bone marrow edema. Knowledge of normal imaging features in children (e.g., flaring, blurring, or irregular appearance of the articular surface) is essential for interpreting sacroiliac joint MRI in children because these normal processes can simulate disease. CLINICAL RELEVANCE STATEMENT: Sacroiliitis is a potentially debilitating disease if not diagnosed and treated promptly, before structural damage to the sacroiliac joints occurs. Imaging has a prominent place in the diagnostic process. We present a summary of practice recommendations for imaging of sacroiliitis, including several new imaging techniques. KEY POINTS: • MRI is the modality of choice for suspected inflammatory sacroiliitis, including a joint-line-specific sequence for optimal evaluation of the bone-cartilage interface to improve detection of erosions. • Radiography and CT (especially low-dose CT) are reasonable alternatives when MRI is unavailable. • Knowledge of normal imaging features in children is mandatory for interpretation of MRI of pediatric sacroiliac joints.

Self-reported diagnostic confidence predicts diagnostic accuracy in axial spondyloarthritis imaging

OBJECTIVES

Reporting diagnostic confidence (DC) in axial spondyloarthritis (axSpA) imaging is recommended by the ASAS guidelines. Our aim was to investigate whether self-reported DC predicts diagnostic accuracy in axSpA imaging using X-ray (XR), computed tomography (CT) and magnetic resonance imaging (MRI).

METHODS

We performed a post hoc analysis including 163 patients with low back pain (89 axSpA and 56 non-axSpA). Nine blinded readers with different experience levels [inexperienced (<1 year), semi-experienced (3-8 years) and experienced (>12 years)] scored the sacroiliac joint images for compatibility with axSpA. DC was reported on a scale from 1 (not sure) to 10 (very sure). Mean DC scores and standard deviations were calculated for correct and incorrect responses using XR, CT, MRI, XR+MRI and CT+MRI. Differences in DC were assessed using the Mann-Whitney U test.

RESULTS

DC scores were higher for correct axSpA diagnoses and differed significantly between correct and incorrect responses for all modalities (P < 0.001), with a mean DC of 7.1 ± 2.1 and 6.3 ± 2.1 for XR, 8.3 ± 1.8 and 6.7 ± 2.0 for CT, 8.1 ± 1.9 and 6.2 ± 1.9 for MRI, 8.2 ± 1.8 and 6.7 ± 1.8 for XR+MRI and 8.4 ± 1.8 and 6.8 ± 1.8 for CT+MRI, respectively. This was also the case when looking at the results by experience group, except for XR in the inexperienced group.

CONCLUSION

Providing self-reported DC in radiological reports is useful information to predict diagnostic reliability in axSpA imaging.

MRI predictors of infectious etiology in patients with unilateral sacroiliitis

BACKGROUND

Unilateral presentation of sacroiliitis is a diagnostic dilemma, especially between infection and inflammatory sacroiliitis associated with spondyloarthritis, requiring an early and accurate diagnosis.

OBJECTIVE

To assess the utility of magnetic resonance imaging (MRI) in differentiating infective versus inflammatory etiology in unilateral sacroiliitis.

MATERIALS AND METHODS

Retrospective review of the MRI of 90 patients with unilateral sacroiliitis, having an established final diagnosis. MR images were evaluated for various bone and soft tissue changes using predefined criteria and analyzed using univariate and multivariate regression analysis.

RESULTS

Among the 90 patients, infective etiology was diagnosed in 66 (73.3%) and inflammatory etiology in 24 (26.7%). Large erosions, both iliac and sacral-sided edema, joint space involvement with effusion or synovitis, soft tissue edema, elevated ESR/CRP, and absence of capsulitis and enthesitis were associated with infection (p < .001). The independently differentiating variables favoring infection on multivariate analysis were-both iliac and sacral-sided edema (OR 4.79, 95% CI: 0.96-23.81, p = .05), large erosions (OR 17.96, 95% CI: 2.66-121.02, p = .003), and joint space involvement (OR 9.9, 95% CI: 1.36-72.06, p = .02). Exclusive features of infection were osteomyelitis, sequestra, abscesses, sinus tracts, large erosions, and multifocality. All infective cases had soft tissue edema, joint space involvement, elevated ESR, and no capsulitis.

CONCLUSION

MRI evaluation for the presence and pattern of bone and joint space involvement, soft tissue involvement, and careful attention to certain exclusive features will aid in differentiating infectious sacroiliitis from inflammatory sacroiliitis.

New Bone Formation in Axial Spondyloarthritis: A Review

Background

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease primarily affecting the sacroiliac joints (SIJs) and the spine. Imaging plays a crucial role in the diagnosis of axSpA, with magnetic resonance imaging (MRI) and radiography being the primary modalities used in clinical practice. New bone formation occurs in both the spine (non-bridging and bridging syndesmophytes, transdiscal ankylosis, and ankylosis of small joints and posterior elements) and the SIJs (backfill and ankylosis). New bone formation indicates advanced axSpA.

Method

This review explores the role of imaging in the diagnosis and monitoring of axSpA, focusing on the significance of new bone formation, and provides an overview of the characteristic imaging findings of new bone formation in axSpA in each imaging modality.

Conclusion

Imaging methods, such as X-ray, MRI, and CT, have different diagnostic accuracies for detecting structural lesions and new bone formation. Each modality has its strengths and weaknesses, and the choice depends on the specific clinical context. Imaging is crucial for the diagnosis and monitoring of axSpA, particularly for the detection of new bone formation. Different imaging techniques provide valuable information about disease progression and treatment response. Understanding the significance of new bone formation and its detection using imaging modalities is essential for the accurate diagnosis and effective management of patients with axSpA.

Key Points

Citation Format

Reporting Sacroiliac Joint Imaging Performed for Known or Suspected Axial Spondyloarthritis: Assessment of SpondyloArthritis International Society Recommendations

Whereas previous projects attempted to standardize imaging in patients with axial spondyloarthritis (axSpA), few studies have been published about the need for specific details regarding the image acquisition and lesions that may be less familiar to general radiologists. This work reports consensus recommendations developed by the Assessment of SpondyloArthritis International Society (ASAS) that aim to standardize the imaging reports in patients suspected of having or with known axSpA. A task force consisting of radiologists and rheumatologists from ASAS and one patient representative formulated two surveys that were completed by ASAS members. The results of these surveys led to the development of 10 recommendations that were endorsed by 73% (43 of 59) of ASAS members. The recommendations are targeted to the radiologist and include best practices for the inclusion of clinical information, technical details, image quality, and imaging findings in radiology reports. These recommendations also emphasize that imaging findings that indicate differential diagnoses and referral suggestions should be included in the concluding section of the radiology report. With these recommendations, ASAS aims to improve the diagnostic process and care for patients suspected of having or with known axSpA.

Prevalence of spondyloarthritis in inflammatory bowel disease according ASAS and ultrassonography and its correlation with plasma calprotectin

BACKGROUND

Enteropathic spondyloarthritis is underdiagnosed and inflammatory biomarkers and ultrasonography (US) could be useful for screening inflammatory bowel disease (IBD) patients. The objective of this study was to evaluate the prevalence of spondyloarthritis (SpA) in IBD patients, according to the Assessment of SpondyloArthritis International Society (ASAS) criteria and the correlation of results of US of entheses and joints with plasma calprotectin levels.

METHODS

This was an observational cross-sectional study. Patients from the IBD outpatient clinic of a reference center were evaluated according to ASAS criteria classification, results of US of entheses and joints, and inflammatory biomarker measurements (erythrocyte sedimentation rates, C-reactive protein levels, fecal and plasma calprotectin levels). A p value lower than 0.05 was considered significant.

RESULTS

A total of 30.5% of the studied sample (n = 118) of patients with IBD presented at least one inflammatory musculoskeletal manifestation. The overall prevalence of enteropathic SpA was 13.55%, with 10.16% axial SpA and 4.23% peripheral SpA according to the ASAS criteria. A total of 42.1% of patients had an MASEI score greater than 18, 35.2% had synovitis, and 14.7% had tenosynovitis on US, increasing the frequency of diagnosis of enteropathic SpA to 22.8%. Plasma calprotectin levels were similar to those in healthy controls, and correlated only with the fecal calprotectin level (p 0.041).

CONCLUSIONS

A total of 13.5% of patients met the criteria in accordance with the ASAS criteria for enteropathic SpA, which increased to 22.8% with the addition of US. The prevalence of enthesitis, synovitis and tenosynovitis by US of symptomatic joints and entheses were 42%, 35% and 14.7% respectively. Plasma calprotectin was correlated with fecal calprotectin but not with inflammatory biomarkers or US or ASAS criteria.

Learning imaging in axial spondyloarthritis: more than just a matter of experience

OBJECTIVE

Reliable interpretation of imaging findings is essential for the diagnosis of axial spondyloarthritis (axSpA) and requires a high level of experience. We investigated experience-dependent differences in diagnostic accuracies using X-ray (XR), MRI and CT.

METHODS

This post hoc analysis included 163 subjects with low back pain. Eighty-nine patients had axSpA, and 74 patients had other conditions (mechanical, degenerative or non-specific low back pain). Final diagnoses were established by an experienced rheumatologist before the reading sessions. Nine blinded readers (divided into three groups with different levels of experience) scored the XR, CT and MRI of the sacroiliac joints for the presence versus absence of axSpA. Parameters for diagnostic performance were calculated using contingency tables. Differences in diagnostic performance between the reader groups were assessed using the McNemar test. Inter-rater reliability was assessed using Fleiss kappa.

RESULTS

Diagnostic performance was highest for the most experienced reader group, except for XR. In the inexperienced and semi-experienced group, diagnostic performance was highest for CT&MRI (78.5% and 85.3%, respectively). In the experienced group, MRI showed the highest performance (85.9%). The greatest difference in diagnostic performance was found for MRI between the inexperienced and experienced group (76.1% vs 85.9%, p=0.001). Inter-rater agreement was best for CT in the experienced group with κ=0.87.

CONCLUSION

Differences exist in the learnability of the imaging modalities for axSpA diagnosis. MRI requires more experience, while CT is more suitable for inexperienced radiologists. However, diagnosis relies on both clinical and imaging information.

Predictors of treatment failure of non-steroidal anti-inflammatory drugs in patients with axial spondyloarthritis with focus on haptoglobin, haptoglobin polymorphism and zonulin

According to the Assessment of SpondyloArthritis International Society-European Alliance of Associations for Rheumatology (ASAS-EULAR) recommendations for the management of axial spondyloarthritis (axSpA), patients should undergo at least two courses of non-steroidal anti-inflammatory drugs (NSAIDs) therapy. In our study, we enrolled axSpA patients both at onset and in a flare who had already been treated with NSAIDs ineffectively. Subsequently, according to the recommendations, they received modified NSAID treatment as another attempt to the first-line drug therapy and were monitored from there. We aimed to identify risk factors for treatment failure after 4 weeks (Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score ≥ 4) especially amongst zonulin and haptoglobin concentrations, and haptoglobin polymorphism. Treatment failure was observed in 71% of patients, and the following variables were contributed for occurrence of this state: higher zonulin levels, ankylosing spondylitis, X-ray sacroiliitis, magnetic resonance imaging sacroiliitis, long duration of symptoms, high BASDAI, and high value of spinal pain intensity on visual analogue scale. In addition, the following positive correlations were found: haptoglobin concentration with C-reactive protein (r = 0.56; p = 0.0004), and erythrocyte sedimentation rate (r = 0.62; p < 0.0001), as well as between zonulin levels and white blood count (r = 0.5; p = 0.0003). The results of the study presented the identified factors related to the standard treatment failure in axSpA, amongst them zonulin levels. They might be applied to point out the patients for whom the search for a more appropriate method of treatment should be considered.

Implementation of artificial intelligence models in magnetic resonance imaging with focus on diagnosis of rheumatoid arthritis and axial spondyloarthritis: narrative review

Early diagnosis in rheumatoid arthritis (RA) and axial spondyloarthritis (axSpA) is essential to initiate timely interventions, such as medication and lifestyle changes, preventing irreversible joint damage, reducing symptoms, and improving long-term outcomes for patients. Since magnetic resonance imaging (MRI) of the wrist and hand, in case of RA and MRI of the sacroiliac joints (SIJ) in case of axSpA can identify inflammation before it is clinically discernible, this modality may be crucial for early diagnosis. Artificial intelligence (AI) techniques, together with machine learning (ML) and deep learning (DL) have quickly evolved in the medical field, having an important role in improving diagnosis, prognosis, in evaluating the effectiveness of treatment and monitoring the activity of rheumatic diseases through MRI. The improvements of AI techniques in the last years regarding imaging interpretation have demonstrated that a computer-based analysis can equal and even exceed the human eye. The studies in the field of AI have investigated how specific algorithms could distinguish between tissues, diagnose rheumatic pathology and grade different signs of early inflammation, all of them being crucial for tracking disease activity. The aim of this paper is to highlight the implementation of AI models in MRI with focus on diagnosis of RA and axSpA through a literature review.

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.

[Computed tomography versus magnetic resonance imaging : Pros and cons in axial spondyloarthritis]

The diagnosis of axial spondyloarthritis depends on direct visualization of the sacroiliitis in addition to clinical assessment and determination of the histocompatibility antigen HLA-B27. While the value of conventional radiographic images has meanwhile been described in many studies as insufficient to diagnose the disease at an early stage, magnetic resonance imaging and also computed tomography now offer the possibility to visualize findings, such as bone marrow edema, erosion, fat metaplasia, backfill and ankylosis. Thus, it is necessary to decide which procedure should be used and when. Furthermore, both cross-sectional imaging techniques are currently undergoing major changes, and technical advancements are making great strides every year. This article provides an overview of which future technologies will be included in the rheumatological diagnostics of the sacroiliac joints. This overview also illustrates which standard methods are established in the diagnostics of axial spondyloarthritis and how they are used.

Radiomics for the Detection of Active Sacroiliitis Using MR Imaging

Detecting active inflammatory sacroiliitis at an early stage is vital for prescribing medications that can modulate disease progression and significantly delay or prevent debilitating forms of axial spondyloarthropathy. Conventional radiography and computed tomography offer limited sensitivity in detecting acute inflammatory findings as these methods primarily identify chronic structural lesions. Conversely, Magnetic Resonance Imaging (MRI) is the preferred technique for detecting bone marrow edema, although it is a complex process requiring extensive expertise. Additionally, ascertaining the origin of lesions can be challenging, even for experienced medical professionals. Machine learning (ML) has showcased its proficiency in various fields by uncovering patterns that are not easily perceived from multi-dimensional datasets derived from medical imaging. The aim of this study is to develop a radiomic signature to aid clinicians in diagnosing active sacroiliitis. A total of 354 sacroiliac joints were segmented from axial fluid-sensitive MRI images, and their radiomic features were extracted. After selecting the most informative features, a number of ML algorithms were utilized to identify the optimal method for detecting active sacroiliitis, leading to the selection of an Extreme Gradient Boosting (XGBoost) model that accomplished an Area Under the Receiver-Operating Characteristic curve (AUC-ROC) of 0.71, thus further showcasing the potential of radiomics in the field.

Clustered Occurrence of Osteitis Condensans Ilii in Patients with Symptomatic Hip Dysplasia

BACKGROUND

Osteitis condensans ilii (OCI) is a relatively rare benign disease of the lower anterior sacroiliac joint (SIJ) region that can cause symptoms such as low back pain (LBP), lateral hip pain and nonspecific hip or thigh pain. Its exact pathoetiology remains to be clarified. The aim of this study is to determine the prevalence of OCI in patients with symptomatic developmental dysplasia of the hip (DDH) undergoing periacetabular osteotomy (PAO) to identify potential clustering of OCI in a with altered biomechanics of hip and SIJs.

METHODS

A retrospective investigation of all patients who underwent periacetabular osteotomy in a tertiary reference hospital from January 2015 to December 2020. Clinical and demographic data were retrieved from the hospital's internal medical records. Radiographs and magnetic resonance images (MRIs) were reviewed for the presence of OCI. A t-test for independent variables was conducted to identify differences between patients with and without OCI. A binary logistic regression model was established to determine the influence of age, sex and body mass index (BMI) on the presence of OCI.

RESULTS

The final analysis included 306 patients (81% female). In 21.2% of the patients (f: 22.6%; m: 15.5%), OCI was present. BMI was significantly higher in patients with OCI (23.7 kg/m² vs. 25.0 kg/m²; p = 0.044). Binary logistic regression revealed that a higher BMI increased the likelihood of sclerosis in typical osteitis condensans locations, OR = 1.104 (95%-CI [1.024, 1.191]), as did female sex, OR = 2.832 (95%-CI [1.091, 7.352].

CONCLUSIONS

Our study revealed a considerably higher prevalence of OCI in patients with DDH than in the general population. Furthermore, BMI was shown to have an influence on the occurrence of OCI. These results support the theory that OCI is attributable to altered mechanical loading of the SIJs. Clinicians should be aware that OCI is common in patients with DDH and a potential cause of LBP, lateral hip pain and nonspecific hip or thigh pain.

Axial Spondyloarthritis and Diagnostic Challenges: Over-diagnosis, Misdiagnosis, and Under-diagnosis

PURPOSE OF REVIEW

This article aims to review the challenges in axial spondyloarthritis diagnosis and identify the possible contributing factors.

RECENT FINDINGS

The inability to reach an accurate diagnosis in a timely fashion can lead to treatment delays and worse disease outcomes. The lack of validated diagnostic criteria and the misuse of the currently available classification criteria could be contributing. There is also significant inter-reader variability in interpreting images, and the radiologic definitions of axial spondyloarthritis continue to be re-defined to improve their positive predictive value. The role of inflammatory back pain features, serologic biomarkers, genetics, and their diagnostic contribution to axial spondyloarthritis continues to be investigated. There is still a significant amount of delay in the diagnosis of axial spondyloarthritis. Appreciating the factors that contribute to this delay is of utmost importance to close the gap. It is similarly important to recognize other conditions that may present with symptoms that mimic axial spondyloarthritis so that misdiagnosis and wrong treatment can be avoided.

Knowledge mapping of biological disease-modifying anti-rheumatic drugs for axial spondyloarthritis: a bibliometric study

Various biological disease-modifying anti-rheumatic drugs (bDMARDs) have been applied for treating axial spondyloarthritis (axSpA). However, there is a glaring absence of a bibliometric analysis on bDMARDs against axSpA. Articles related to use of bDMARDs in treating axSpA published from 2004 to 2022 were searched from the Web of Science Core Collection. VOS viewer 1.6.18 and CiteSpace 6.1.R2 were used to analyze and visualize the quantity and citations of publications, as well as to identify "research hotspots" and trends in this field. BibExcel version 1.0.0 and gCLUTO version 1.0 were used to build matrices for bi-clustering analysis. A total of 2546 articles referring to bDMARDs for treatment of axSpA were included in this bibliometric analysis. Overall, the number of publications has been increasing steadily annually. The USA (23.21%, 591 publications) ranked first with the largest output of papers, followed by Germany, and the Netherlands. Rheumazentrum Ruhrgebiet ranked first as the most frequent publisher (119 articles). Annals of the Rheumatic Diseases published the most documents (6.76%, 172 publications) in this field. The predominant hotspots have been "tuberculosis," "IL-17," and "quality of life" in the field until 2020. Since 2015, "biosimilar pharmaceuticals" has retained the popularity. Current research hotspots are "spinal radiographic progression," Janus kinase (JAK) inhibitors, and adverse events (AEs). Machine learning has become popular gradually. Globally, there has been a steady increase in the number of studies on bDMARDs use against axSpA. JAK inhibitors, spinal radiographic progression, biosimilar pharmaceuticals, and AEs are current research hotspots. Machine learning is emerging research hotspots and trends in this field.

Sex Disparities of the Sacroiliac Joint: Focus on Joint Anatomy and Imaging Appearance

The sacroiliac joint (SIJ) is an anatomically complex joint which, as a functional unit with the pelvis and spine, is of decisive biomechanical importance for the human body. It is also a commonly overlooked source of lower back pain. Like the entire bony pelvis, the SIJ exhibits major sexual dimorphisms; thus, the sex-dependent evaluation of this joint is becoming increasingly important in clinical practice, both anatomically with joint shape variations and biomechanical differences as well as in terms of image appearance. The influence of the SIJ shape, which differs in women and men, is crucial for the different biomechanical joint properties. These differences are important in the development of joint diseases at the SIJ, which shows a specific difference between the sexes. This article aims to provide an overview of sex disparities of the SIJ regarding different anatomical and imaging appearances to further understand the insights into the interplay of sex differences and SIJ disease.

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.