Comparison of MRI with radiography for detecting structural lesions of the sacroiliac joint using CT as standard of reference: results from the SIMACT study

Characterization of bone marrow lesions in axial spondyloarthritis using quantitative T1 mapping MRI

OBJECTIVE

Conventional magnetic resonance imaging (MRI) uses T1-weighted and short-tau inversion recovery (STIR) sequences to characterize bone marrow in axial spondyloarthritis. However, quantification is restricted to estimating the extent of lesions because signal intensities are highly variable both within individuals and across patients and MRI scanners. This study evaluates the performance of quantitative T1 mapping for distinguishing different types of bone marrow lesions of the sacroiliac joints.

MATERIALS AND METHODS

In this prospective study, 62 patients underwent computed tomography (CT) and MRI of the sacroiliac joints including T1, STIR, and T1 mapping. Bone marrow lesions were characterized by three readers and assigned to one of four groups: sclerosis, osteitis, fat lesions, and mixed marrow lesions. Relaxation times on T1 maps were compared using generalized estimating equations and receiver operating characteristics (ROC) analysis.

RESULTS

A total of 119 lesions were selected (sclerosis: 38, osteitis: 27, fat lesions: 40; mixed lesions: 14). T1 maps showed highly significant differences between the lesions with the lowest values for sclerosis (1516±220 ms), followed by osteitis (1909±75 ms), and fat lesions (2391±200 ms); p<0.001. T1 mapping differentiated lesions with areas under the ROC curve of 99% (sclerosis vs. osteitis) and 100% (other comparisons).

CONCLUSION

T1 mapping allows accurate characterization of sclerosis, osteitis, and fat lesions at the sacroiliac joint but only for homogeneous, non-mixed lesions. Thus, further sequence development is needed before implementation in clinical routine.

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.

Diagnosis, monitoring, and management of axial spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic condition predominantly affecting the spine and sacroiliac joints. This article provides an in-depth overview of the current approaches to diagnosing, monitoring, and managing axSpA, including insights into developing terminology and diagnostic difficulties. A substantial portion of the debate focuses on the challenging diagnostic procedure, noting the difficulty of detecting axSpA early, particularly before the appearance of radiologic structural changes. Despite normal laboratory parameters, more than half of axSpA patients experience symptoms. X-ray and magnetic resonance imaging (MRI) are essential for evaluating structural damage and inflammation. MRI can be beneficial when there is no visible structural damage on X-ray as it can help unravel bone marrow edema (BME) as a sign of ongoing inflammation. The management covers both non-pharmacological and pharmacological approaches. Lifestyle modifications, physical activity, and patient education are essential components of the management. Pharmacological therapy, including nonsteroidal anti-inflammatory drugs (NSAIDs) and biologic disease-modifying anti-rheumatic drugs (bDMARDs), are explored, emphasizing individualized treatment. To effectively manage axSpA, a comprehensive and well-coordinated approach is necessary, emphasizing the significance of a multidisciplinary team. Telehealth applications play a growing role in axSpA management, notably in reducing diagnostic delays and facilitating remote monitoring. In conclusion, this article underlines diagnostic complexities and emphasizes the changing strategy of axSpA treatment. The nuanced understanding offered here is designed to guide clinicians, researchers, and healthcare providers toward a more comprehensive approach to axSpA diagnosis and care.

Erosions on T1-Weighted Magnetic Resonance Imaging Versus Radiography of Sacroiliac Joints in Recent-Onset Axial Spondyloarthritis: 2-Year Data (EMBARK Trial and DESIR Cohort)

OBJECTIVE

(1) To compare the capacity to detect sacroiliac joint (SIJ) erosions and baseline-to-week 104 change in erosions between magnetic resonance imaging (MRI) and radiographs in recent-onset axial spondyloarthritis (axSpA); and (2) to compare treatment-discriminatory capacities of MRI and radiographic scores for erosion detection in patients receiving etanercept in the Effect of Etanercept on Symptoms and Objective Inflammation in Nonradiographic axSpA (EMBARK) trial vs controls in the DESIR (Devenir des Spondylarthropathies Indifférenciées Récentes) cohort.

METHODS

Anonymized SIJ MRI and radiographs were assessed at patient and joint surface levels. Three readers evaluated MRI; 3 different readers evaluated radiographs. Final scores for comparison of radiographs and MRI for detection of erosions were assigned based on agreement of ≥ 2 of 3 readers' assessments.

RESULTS

At baseline, discordance in erosion detection between imaging methods was more frequent for MRI erosions in the absence of radiographic erosions (48/224 [21.4%] patients) than for radiographic erosions in the absence of MRI erosions (14/224 [6.3%] patients; P < 0.001). After 104 weeks, a decrease in erosions was observed on MRI but not radiographs in 49/221 (22.2%) patients, and on radiographs but not MRI in 6/221 (2.7%) patients (P < 0.001). In the treatment-discriminant capacity analysis, the largest standardized differences between etanercept and control cohorts at week 104 were changes in Spondyloarthritis Research Consortium of Canada MRI erosion discrete score, changes in erosion average score, and meeting the modified New York criteria on radiographs, with unadjusted/adjusted Hedges G effect sizes of 0.40/0.50, 0.40/0.56, and 0.40/0.43, respectively.

CONCLUSION

In recent-onset axSpA, SIJ erosions and erosion change were observed more frequently on MRI than radiography. The significance of interval improvement of MRI erosions warrants further research. [ClinicalTrials.gov: NCT01258738, NCT01648907].

Detection of structural lesions of the sacroiliac joints in patients with spondyloarthritis: A comparison of T1-weighted 3D spoiled gradient echo MRI and MRI-based synthetic CT versus T1-weighted turbo spin echo MRI

OBJECTIVES

To investigate the detection of erosion, sclerosis and ankylosis using 1 mm 3D T1-weighted spoiled gradient echo (T1w-GRE) MRI and 1 mm MRI-based synthetic CT (sCT), compared with conventional 4 mm T1w-TSE.

MATERIALS AND METHODS

Prospective, cross-sectional study. Semi-coronal 4 mm T1w-TSE and axial T1w-GRE with 1.6 mm slice thickness and 0.8 mm spacing between overlapping slices were performed. The T1w-GRE images were processed into sCT images using a commercial deep learning algorithm, BoneMRI. Both were reconstructed into 1 mm semi-coronal images. T1w-TSE, T1w-GRE and sCT images were assessed independently by 3 expert and 4 non-expert readers for erosion, sclerosis and ankylosis. Cohen's kappa for inter-reader agreement, exact McNemar test for lesion frequencies and Wilcoxon signed-rank test for confidence in lesion detection were used.

RESULTS

Nineteen patients with axial spondyloarthritis were evaluated. T1w-GRE increased inter-reader agreement for detecting erosion (kappa 0.42 vs 0.21 in non-experts), increased detection of erosion (57 vs 43 of 152 joint quadrants) and sclerosis (26 vs 17 of 152 joint quadrants) among experts, and increased reader confidence for scoring erosion and sclerosis. sCT increased inter-reader agreement for detecting sclerosis (kappa 0.69 vs 0.37 in experts) and ankylosis (0.71 vs 0.52 in non-experts), increased detection of sclerosis (34 vs 17 of 152 joint quadrants) and ankylosis (20 vs 13 of 76 joint halves) among experts, and increased reader confidence for scoring erosion, sclerosis and ankylosis.

CONCLUSION

T1w-GRE and sCT increase sensitivity and reader confidence for the detection of erosion, sclerosis and ankylosis, compared with T1w-TSE.

CLINICAL RELEVANCE STATEMENT

These methods improve the detection of sacroiliac joint structural lesions and might be a useful addition to SIJ MRI protocols both in routine clinical care and as structural outcome measures in clinical trials.

MRI-based synthetic CT: a new method for structural damage assessment in the spine in patients with axial spondyloarthritis - a comparison with low-dose CT and radiography

OBJECTIVE

To investigate the ability of MRI-based synthetic CT (sCT), low-dose CT (ldCT) and radiography to detect spinal new bone formation (NBF) in patients with axial spondyloarthritis (axSpA).

METHODS

Radiography of lumbar and cervical spine, ldCT and sCT of the entire spine were performed in 17 patients with axSpA. sCT was reconstructed using the BoneMRI application (V.1.6, MRIGuidance BV, Utrecht, NL), a quantitative three-dimensional MRI-technique based on a dual-echo gradient sequence and a machine learning processing pipeline that can generate CT-like MR images. Images were anonymised and scored by four readers blinded to other imaging/clinical information, applying the Canada-Denmark NBF assessment system.

RESULTS

Mean scores of NBF lesions for the four readers were 188/209/37 for ldCT/sCT/radiography. Most NBF findings were at anterior vertebral corners with means 163 on ldCT, 166 on sCT and 35 on radiography. With ldCT of the entire spine as reference standard, the sensitivity to detect NBF was 0.67/0.13 for sCT/radiography; both with specificities >0.95. For levels that were assessable on radiography (C2-T1 and T12-S1), the sensitivity was 0.61/0.48 for sCT/radiography, specificities >0.90. For facet joints, the sensitivity was 0.46/0.03 for sCT/radiography, specificities >0.94. The mean inter-reader agreements (kappa) for all locations were 0.68/0.58/0.56 for ldCT/sCT/radiography, best for anterior corners.

CONCLUSION

With ldCT as reference standard, MRI-based sCT of the spine showed very high specificity and a sensitivity much higher than radiography, despite limited reader training. sCT could become highly valuable for detecting/monitoring structural spine damage in axSpA, not the least in clinical trials.

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.

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.

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.

Beyond the horizon: Innovations and future directions in axial-spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease of the spine and sacroiliac joints. This review discusses recent advances across multiple scientific fields that promise to transform axSpA management. Traditionally, axSpA was considered an immune-mediated disease driven by human leukocyte antigen B27 (HLA-B27), interleukin (IL)-23/IL-17 signaling, biomechanics, and dysbiosis. Diagnosis relies on clinical features, laboratory tests, and imaging, particularly magnetic resonance imaging (MRI) nowadays. Management includes exercise, lifestyle changes, non-steroidal anti-inflammatory drugs and if this is not sufficient to achieve disease control also biological and targeted-synthetic disease modifying anti-rheumatic drugs. Beyond long-recognized genetic risks like HLA-B27, high-throughput sequencing has revealed intricate gene-environment interactions influencing dysbiosis, immune dysfunction, and aberrant bone remodeling. Elucidating these mechanisms promises screening approaches to enable early intervention. Advanced imaging is revolutionizing the assessment of axSpA's hallmark: sacroiliac bone-marrow edema indicating inflammation. Novel magnetic resonance imaging (MRI) techniques sensitively quantify disease activity, while machine learning automates complex analysis to improve diagnostic accuracy and monitoring. Hybrid imaging like synthetic MRI/computed tomography (CT) visualizes structural damage with new clarity. Meanwhile, microbiome analysis has uncovered gut ecosystem alterations that may initiate joint inflammation through HLA-B27 misfolding or immune subversion. Correcting dysbiosis represents an enticing treatment target. Moving forward, emerging techniques must augment patient care. Incorporating patient perspectives will be key to ensure innovations like genetics, microbiome, and imaging biomarkers translate into improved mobility, reduced pain, and increased quality of life. By integrating cutting-edge, multidisciplinary science with patients' lived experience, researchers can unlock the full potential of new technologies to deliver transformative outcomes. The future is bright for precision diagnosis, tightly controlled treatment, and even prevention of axSpA.

New bone formation at the sacroiliac joint in axial spondyloarthritis: characterization of backfill in MRI and CT

OBJECTIVE

MRI findings of the SI joint space in axial SpA (axSpA) include inflammation and fat metaplasia inside an erosion; the latter is also termed 'backfill'. We compared such lesions with CT to better characterize whether they represent new bone formation.

METHODS

We identified patients with axSpA who underwent both CT and MRI of the SI joints in two prospective studies. MRI datasets were jointly screened by three readers for joint space-related findings and grouped into three categories: type A-high short tau inversion recovery (STIR) and low T1 signal; type B-high signal in both sequences; type C-low STIR and high T1 signal. Image fusion was used to identify MRI lesions in CT before we measured Hounsfield units (HU) in each lesion and surrounding cartilage and bone.

RESULTS

Ninety-seven patients with axSpA were identified and we included 48 type A, 88 type B, and 84 type C lesions (maximum 1 lesion per type and joint). The HU values were 73.6 (s.d. 15.0) for cartilage, 188.0 (s.d. 69.9) for spongious bone, 1086.0 (s.d. 100.3) for cortical bone, 341.2 (s.d. 96.7) for type A, 359.3 (s.d. 153.5) for type B and 446.8 (s.d. 123.0) for type C lesions. Lesion HU values were significantly higher than those for cartilage and spongious bone, but lower than those for cortical bone (P < 0.001). Type A and B lesions showed similar HU values (P = 0.93), whereas type C lesions were denser (P < 0.001).

CONCLUSION

All joint space lesions show increased density and might contain calcified matrix, suggesting new bone formation, with a gradual increase in the proportion of calcified matrix towards type C lesions (backfill).

T1-weighted images-based radiomics for structural lesions evaluation in patients with suspected axial spondyloarthritis

PURPOSE

The aim of this study was to investigate the feasibility of radiomics based on T1-weighted images (T1WI) for assessing sacroiliac joint (SIJ) structural lesions in patients with suspected axial spondyloarthritis (axSpA).

MATERIALS AND METHODS

A total of 266 patients with clinical suspicion of axSpA between December 2016 and January 2022 were enrolled. Structural lesions were assessed on low-dose CT (ldCT) and MRI, respectively. Radiomic features, extracted from SIJ T1WI, were included to generate the radiomics model. The performance of the radiomics model was evaluated using receiver operating characteristic (ROC) curve. Furthermore, point-biserial correlation analysis was used to interpret the associations between the radiomic feature and structural lesions.

RESULTS

Using ldCT as the reference standard, the radiomics model showed favorable performance for detecting positive global structural lesions in the training cohort (AUC, 0.82 [95% CI: 0.76, 0.88]) and validation cohort (AUC, 0.82 [95% CI: 0.72, 0.91]. Experienced MRI raters yielded predictive AUCs of 0.73 (95% CI: 0.67, 0.79), and 0.74 (95% CI: 0.66, 0.83) in the training and validation cohort, respectively. The seven radiomic features included in the radiomics model showed significant correlation with different kinds of structural lesions (P all < 0.05). Among them, Wavelet.LHL_firstorder_90Percentile showed the strongest association with fat lesion (r = 0.48, P < 0.05).

CONCLUSION

The radiomics analysis with T1WI could effectively detect SIJ structural lesions and achieved expert-level performance. Each radiomic feature was correlated with different structural lesions significantly, which might inform radiomic-based applications for axSpA intelligent diagnosis.

Neural network algorithm for detection of erosions and ankylosis on CT of the sacroiliac joints: multicentre development and validation of diagnostic accuracy

OBJECTIVES

To evaluate the feasibility and diagnostic accuracy of a deep learning network for detection of structural lesions of sacroiliitis on multicentre pelvic CT scans.

METHODS

Pelvic CT scans of 145 patients (81 female, 121 Ghent University/24 Alberta University, 18-87 years old, mean 40 ± 13 years, 2005-2021) with a clinical suspicion of sacroiliitis were retrospectively included. After manual sacroiliac joint (SIJ) segmentation and structural lesion annotation, a U-Net for SIJ segmentation and two separate convolutional neural networks (CNN) for erosion and ankylosis detection were trained. In-training validation and tenfold validation testing (U-Net-n = 10 × 58; CNN-n = 10 × 29) on a test dataset were performed to assess performance on a slice-by-slice and patient level (dice coefficient/accuracy/sensitivity/specificity/positive and negative predictive value/ROC AUC). Patient-level optimisation was applied to increase the performance regarding predefined statistical metrics. Gradient-weighted class activation mapping (Grad-CAM++) heatmap explainability analysis highlighted image parts with statistically important regions for algorithmic decisions.

RESULTS

Regarding SIJ segmentation, a dice coefficient of 0.75 was obtained in the test dataset. For slice-by-slice structural lesion detection, a sensitivity/specificity/ROC AUC of 95%/89%/0.92 and 93%/91%/0.91 were obtained in the test dataset for erosion and ankylosis detection, respectively. For patient-level lesion detection after pipeline optimisation for predefined statistical metrics, a sensitivity/specificity of 95%/85% and 82%/97% were obtained for erosion and ankylosis detection, respectively. Grad-CAM++  explainability analysis highlighted cortical edges as focus for pipeline decisions.

CONCLUSIONS

An optimised deep learning pipeline, including an explainability analysis, detects structural lesions of sacroiliitis on pelvic CT scans with excellent statistical performance on a slice-by-slice and patient level.

CLINICAL RELEVANCE STATEMENT

An optimised deep learning pipeline, including a robust explainability analysis, detects structural lesions of sacroiliitis on pelvic CT scans with excellent statistical metrics on a slice-by-slice and patient level.

KEY POINTS

• Structural lesions of sacroiliitis can be detected automatically in pelvic CT scans. • Both automatic segmentation and disease detection yield excellent statistical outcome metrics. • The algorithm takes decisions based on cortical edges, rendering an explainable solution.

Comparison of sacroiliac CT findings in patients with and without ankylosing spondylitis aged over 50 years

Diagnosis of axial spondyloarthritis (axSpA) is nowadays commonly made with the help of pelvic radiography or magnetic resonance imaging (MRI). However, there is an important inter-observer variability in radiography, and MRI is subject to possible false positives and is not the best modality for studying structural lesions. Conversely, pelvic computed tomography (CT) has excellent specificity and appears to be more effective than radiography for the diagnosis of ankylosing spondylitis (AS). However, its findings in patients over 50 years of age have not yet been studied. The objectives of this study were to describe the CT characteristics of sacro-iliac joints (SIJ) and the presence of intra-articular gas in patients with AS aged over 50 years and to compare them with controls of the same age and sex. This two-center, cross-sectional, observational study was performed using the medical records of the rheumatology departments of two University Hospitals. We included patients with a clinical diagnosis of axSpA, who had both definite radiographic sacroiliitis according to the modified New York criteria and met the ASAS 2009 criteria for axSpA (that is, AS), and who had undergone any CT scan including the whole SIJ. Each patient was matched for age and sex to a control randomly selected on the Picture Archiving and Communication System (PACS), symptomatic or asymptomatic, and without spondyloarthritis. For each individual, CT scans were interpreted blindly by two independent rheumatologists and scored for joint space narrowing (JSN), erosions, sclerosis, intra-articular gas, and diffuse idiopathic skeletal hyperostosis (DISH). Ninety patients and 90 controls were included in the study. The rates of positive JSN, erosion, and sclerosis scores were higher in the AS group (91% vs. 21%, p < 0.0001; 31% vs. 2%, p < 0.0001; 27% vs. 13%, p = 0.03, respectively), but the rates of intra-articular gas and DISH were higher in the control group (24% vs. 68%, p < 0.0001; 7% vs. 33%, p < 0.0001, respectively). 58% of patients had complete bilateral ankylosis. A total of 83 (92.2%) patients had a CT scan considered positive for AS, compared with only seven controls (7.8%). Sclerosis and erosions were predominantly on the anterosuperior part and iliac side of the joint in controls and were more diffuse in patients with AS. CT findings in patients with AS over 50 years of age are mostly represented by changes in the joint space; patients with AS have more erosions and sclerosis changes, but less intra-articular gas than controls.

Current Role of Conventional Radiography of Sacroiliac Joints in Adults and Juveniles with Suspected Axial Spondyloarthritis: Opinion from the ESSR Arthritis and Pediatric Subcommittees

This opinion article by the European Society of Musculoskeletal Radiology Arthritis and Pediatric Subcommittees discusses the current use of conventional radiography (CR) of the sacroiliac joints in adults and juveniles with suspected axial spondyloarthritis (axSpA). The strengths and limitations of CR compared with magnetic resonance imaging (MRI) and computed tomography (CT) are presented.Based on the current literature and expert opinions, the subcommittees recognize the superior sensitivity of MRI to detect early sacroiliitis. In adults, supplementary pelvic radiography, low-dose CT, or synthetic CT may be needed to evaluate differential diagnoses. CR remains the method of choice to detect structural changes in patients with suspected late-stage axSpA or established disease and in patients with suspected concomitant hip or pubic symphysis involvement. In children, MRI is the imaging modality of choice because it can detect active as well as structural changes and is radiation free.

Automatic Image Segmentation and Grading Diagnosis of Sacroiliitis Associated with AS Using a Deep Convolutional Neural Network on CT Images

Ankylosing spondylitis (AS) is a chronic inflammatory disease that causes inflammatory low back pain and may even limit activity. The grading diagnosis of sacroiliitis on imaging plays a central role in diagnosing AS. However, the grading diagnosis of sacroiliitis on computed tomography (CT) images is viewer-dependent and may vary between radiologists and medical institutions. In this study, we aimed to develop a fully automatic method to segment sacroiliac joint (SIJ) and further grading diagnose sacroiliitis associated with AS on CT. We studied 435 CT examinations from patients with AS and control at two hospitals. No-new-UNet (nnU-Net) was used to segment the SIJ, and a 3D convolutional neural network (CNN) was used to grade sacroiliitis with a three-class method, using the grading results of three veteran musculoskeletal radiologists as the ground truth. We defined grades 0-I as class 0, grade II as class 1, and grades III-IV as class 2 according to modified New York criteria. nnU-Net segmentation of SIJ achieved Dice, Jaccard, and relative volume difference (RVD) coefficients of 0.915, 0.851, and 0.040 with the validation set, respectively, and 0.889, 0.812, and 0.098 with the test set, respectively. The areas under the curves (AUCs) of classes 0, 1, and 2 using the 3D CNN were 0.91, 0.80, and 0.96 with the validation set, respectively, and 0.94, 0.82, and 0.93 with the test set, respectively. 3D CNN was superior to the junior and senior radiologists in the grading of class 1 for the validation set and inferior to expert for the test set (P < 0.05). The fully automatic method constructed in this study based on a convolutional neural network could be used for SIJ segmentation and then accurately grading and diagnosis of sacroiliitis associated with AS on CT images, especially for class 0 and class 2. The method for class 1 was less effective but still more accurate than that of the senior radiologist.

[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.

Comparison of Sacroiliitis Grade Readings on the Same Plain Radiographs by the Same Observer at Different Periods

BACKGROUND

 This study aimed to investigate whether there is a difference between the readings of plain sacroiliac radiographs of patients with sacroiliitis by the same observer.

MATERIALS AND METHODS

 In the study, we included patients diagnosed with sacroiliitis through sacroiliac MRI who had undergone plain radiographs at our center between 2015 and 2022. The radiographic grading of patients was conducted by transferring their demographic and clinical information into a computerized environment so that these details would not be identifiable. The plain radiographs were numbered, and the responses were graded as grade 0, 1, 2, 3, or 4 for the right and left sacroiliac joints. The next day, using the same procedure, the same clinician re-evaluated the same plain radiographs in a different order without viewing the previous responses. This method was employed to prevent bias. The results (kappa value) were evaluated (0.00-0.20: slight agreement, 0.21-0.40: fair agreement, 0.41-0.60: moderate agreement, 0.61-0.80: substantial agreement, 0.81-1.00: perfect agreement).

RESULTS

 The study population included 478 patients and 956 sacroiliac joints from plain radiographs, both on the right and left. Following the observer's classification of the sacroiliac joints into 0, 1, 2, 3, and 4, a moderate level of agreement was found in the second evaluation of the same observer a day later with the same grades (p<0.001, kappa: 0.576). When categorized as grade 0-1 and grade 2-4, there was moderate agreement (p<0.001, kappa: 0.519), and categorization into grades 0-2 and 3-4 showed substantial agreement (p<0.001, kappa: 0.715). Analyzing the categorization into grades 0-3 and grade 4 revealed a higher kappa value, indicating substantial agreement (p<0.001, kappa: 0.766).

CONCLUSION

Intraobserver interpretation of radiographs may be more accurate than the interpretation of different specialists. While interpreting plain radiographs, we observed variability between adjacent grades but less variability between distant grades. However, these results need to be validated.

Is it time to move on from pelvic radiography as the first-line imaging modality for suspected sacroiliitis?

PURPOSE OF REVIEW

Pelvic radiography in which structural lesions characteristic of sacroiliitis can be detected, is recommended as the first imaging modality when axial spondyloarthritis (axSpA) is suspected clinically. However, cross-sectional modalities like computed tomography (CT) and magnetic resonance imaging (MRI) are superior to radiographs for diagnosing sacroiliitis. Thus, we currently debate the role of radiography as first imaging modality in the diagnostic workup of axSpA.

RECENT FINDINGS

Diagnosing sacroiliitis on pelvic radiographs is challenging with large interobserver and intraobserver variation. Low-dose CT (ldCT) of the sacroiliac joints (SIJs) was proved to be more sensitive and reliable than radiographs with comparable ionizing radiation exposure. MRI is the preferred modality for detecting early SIJ inflammation, well before structural lesions evolve. New, promising MRI sequences sensitive to cortical bone improve erosion detection, making MRI a one-stop shop for the diagnosis of sacroiliitis.

SUMMARY

Given the debatable additive value of pelvic radiographs for the detection of sacroiliitis, and the presence of excellent alternatives for imaging the bony cortex of the SIJs such as ldCT and MRI with state-of-the-art sequences sensitive to cortical bone, it is high time to discuss the use of these more accurate modalities instead of radiographs.

Zero echo time MRI improved detection of erosions and sclerosis in the sacroiliac joint in comparison with LAVA-flex

Background

T1-weighted spoiled 3D Gradient Recalled Echo pulse sequences, exemplified by Liver Acquisition with Volume Acceleration-flexible MRI (LAVA-Flex), are currently the preferred MR sequence for detecting erosions of the sacroiliac joint (SIJ). However, zero echo time MRI (ZTE) is recently reported to provide excellent visualization of the cortical bone.

Purpose

To directly compare the diagnostic accuracy of ZTE and LAVA-Flex in the detection of structural lesions of the SIJ, including erosions, sclerosis and joint space changes.

Materials and methods

Two readers independently reviewed the ldCT, ZTE and LAVA-Flex images of 53 patients diagnosed as axSpA and scored the erosions, sclerosis and joint space changes. Sensitivity, specificity and Cohen's kappa (κ) of ZTE and LAVA-Flex were calculated, while McNemar's test was employed to compare the two sequences for the positivity of detecting the structural lesions.

Results

Analysis of diagnostic accuracy showed a higher sensitivity of ZTE in comparison with LAVA-Flex in the depiction of erosions (92.5% vs 81.5%, p<0.001), especially first-degree erosions (p<0.001) and second-degree erosions (p<0.001), as well as sclerosis (90.6% vs 71.2%, p<0.001), but not joint space changes (95.2% vs 93.8%, p=0.332). Agreement with ldCT was also higher in ZTE in the detection of erosions than LAVA-Flex as indicated by the κ values (0.73 vs 0.47), as well as in the detection of sclerosis (0.92 vs 0.22).

Conclusion

With ldCT as the reference standard, ZTE could improve diagnostic accuracy of erosions and sclerosis of the SIJ in patients suspected of axSpA, in comparison with LAVA-Flex.

Novel insights into the anatomy and histopathology of the sacroiliac joint and correlations with imaging signs of sacroiliitis in case of axial spondyloarthritis

For a better understanding of the pathophysiology of spondyloarthropathy (SpA), a detailed anatomical description of the sacroiliac joint is required because sacroiliitis is the earliest and most common sign of SpA and an essential feature for the diagnosis of ankylosing spondylitis. Beyond the anatomy, the histopathology of sacroiliac entheses and immunological mechanisms involved in sacroiliitis are crucial for a better understanding of disease causation. In this narrative review, we discuss the core anatomical, histological, and immunohistological observations involved in the development of sacroiliitis, focusing particularly on imaging-based information associated with sacroiliitis. Finally, we try to answer the question of whether at the sacroiliac joint, enthesitis precedes synovitis and subchondral bone changes in SpA.

Anatomical variation of the sacroiliac joint carries an increased risk for erosion and bone marrow oedema in axial spondyloarthritis

OBJECTIVES

To assess the impact of joint shape variations on inflammatory lesions on SI joint MRIs in patients with axial spondyloarthritis (axSpA).

METHODS

A total of 1194 patients from four different prospective cohorts were evaluated, with 684 (57.3%) having sufficient imaging data for inclusion (379 axSpA, 305 controls). All images were evaluated for joint form, erosion, sclerosis, fat metaplasia and bone marrow oedema (BMO) by two independent readers. Logistic regression analyses were used to assess the association of joint form and lesions on imaging for axSpA patients and controls.

RESULTS

Atypical joint forms were common in both axSpA (43.5% [154/354]) and control patients (44.2% [134/303]); both intra-articular variants and a crescent joint shape were significantly more common in axSpA patients (18.4% vs 11.6% and 11.0% vs 5.3.%, respectively; P < 0.001). The axSpA patients with intra-articular joint form variants had 2-fold higher odds of exhibiting erosions [odds ratio (OR) 2.09 (95% CI 1.18, 3.69)] and BMO [OR 1.79 (95% CI 1.13, 2.82)]; this association was not observed in controls. Accessory joints increased the odds for sclerosis in axSpA patients [OR 2.54 (95% CI 1.10, 5.84)] and for sclerosis [OR 17.91 (95% CI 6.92, 46.37)] and BMO [OR 2.05 (95% CI 1.03, 4.07)] in controls.

CONCLUSIONS

Joint form variations are associated with the presence of inflammatory lesions on SI joint MRIs of axSpA patients. This should be taken into consideration in future research on the interplay of mechanical strain and inflammation in axSpA.

Dual-Energy-CT for Osteitis and Fat Lesions in Axial Spondyloarthritis: How Feasible Is Low-Dose Scanning?

BACKGROUND

To assess the ability of low-dose dual-energy computed tomography (ld-DECT) virtual non-calcium (VNCa) images for detecting bone marrow pathologies of the sacroiliac joints (SIJs) in patients with axial spondyloarthritis (axSpA). Material and Methods: Sixty-eight patients with suspected or proven axSpA underwent ld-DECT and MRI of the SIJ. VNCa images were reconstructed from DECT data and scored for the presence of osteitis and fatty bone marrow deposition by two readers with different experience (beginner and expert). Diagnostic accuracy and correlation (Kohen's k) with magnetic resonance imaging (MRI) as the reference standard were calculated for the overall and for each reader separately. Furthermore, quantitative analysis was performed using region-of-interest (ROI) analysis. Results: Twenty-eight patients were classified as positive for osteitis, 31 for fatty bone marrow deposition. DECT's sensitivity (SE) and specificity (SP) were 73.3% and 44.4% for osteitis and 75% and 67.3% for fatty bone lesions, respectively. The expert reader achieved higher diagnostic accuracy for both osteitis (SE 93.33%; SP: 51.85%) and fatty bone marrow deposition (SE: 65%; SP: 77.55%) than the beginner (SE: 26.67%; SP: 70.37% for osteitis; SE: 60%; SP: 44.9% for fatty bone marrow deposition). Overall correlation with MRI was moderate (r = 0.25, p = 0.04) for osteitis and fatty bone marrow deposition (r = 0.25, p = 0.04). Fatty bone marrow attenuation in VNCa images (mean: -129.58 HU; ±103.61 HU) differed from normal bone marrow (mean: 118.84 HU, ±99.91 HU; p < 0.01) and from osteitis (mean: 172 HU, ±81.02 HU; p < 0.01) while osteitis did not differ significantly from normal bone marrow (p = 0.27). Conclusion: In our study, low-dose DECT failed to detect osteitis or fatty lesions in patients with suspected axSpA. Thus, we conclude that higher radiation might be needed for DECT-based bone marrow analysis.

Detection of erosions and fat metaplasia of the sacroiliac joints in patients with suspected sacroiliitis using a chemical shift-encoded sequence (IDEAL-IQ)

PURPOSE

To evaluate the performance of a chemical shift-encoded sequence called IDEAL-IQ for detecting sacroiliac joint (SIJ) erosions and fat metaplasia compared to T1-weighted fast spin echo (T1 FSE) using qualitative and quantitative analysis.

METHOD

Thirty-four patients with suspicion of sacroiliitis who underwent both MRI and CT were included. Each SIJ was divided into four quadrants for analysis. For qualitative analysis, the diagnostic performance of IDEAL-IQ and T1 FSE for erosions were compared by the McNemar test, using CT as the gold standard. Cochran's Q and McNemar tests were used to determine differences in structural changes detected by different imaging methods. For quantitative analysis, two-sample t test and receiver operating characteristic (ROC) analysis were used for the analysis of histogram parameters of proton density fat fraction (PDFF).

RESULTS

Diagnostic sensitivity and accuracy of IDEAL-IQ were greater than T1 FSE for erosions (all P < 0.05). IDEAL-IQ and CT detected more erosions than T1 FSE (all P < 0.05). IDEAL-IQ did not statistically significantly differ from T1 FSE for the detection of fat metaplasia (P = 0.678). All histogram parameters were different between groups with and without fat metaplasia (all P < 0.05) and could distinguish the two groups (all P < 0.05). PDFF_75th was the most effective histogram parameter.

CONCLUSION

IDEAL-IQ detects SIJ erosions with better accuracy than T1 FSE and is similar to T1 FSE for detection of fat metaplasia, enabling further quantitative analysis of the latter via histogram analysis.

Computed tomography-based assessment of radiographic progression in spine and sacroiliac joints after pregnancy in women with radiographic axial spondyloarthritis

Background

Mechanical stress are one of the pathogenesis of axial spondyloarthritis (axSpA). During pregnancy, the mechanical overload on the spine and pelvis increases due to gravid uterus. We aimed to investigate whether pregnancy affects radiographic progression in patients with radiographic axSpA (r-axSpA) based on computed tomography (CT) evaluations.

Materials and methods

This retrospective study included women with r-axSpA aged 19-49 years who underwent at least two CT evaluations of the whole spine and/or sacroiliac joints (SIJs) at intervals of 2-4 years. To compare radiographic progression after delivery, we classified the patients into two groups: delivery group and controls. The delivery group was restricted to women who had the first CT ∼2 years before delivery and the second CT ∼2 years after delivery. The CT Syndesmophyte Score (CTSS) (0-522) and SIJ scores (0-40) were used to evaluate spinal syndesmophytes and erosion, joint space narrowing, and sclerosis of the SIJs.

Results

A total of 21 women in the delivery group and 38 women in the control group were included. The median (Q1-Q3) CTSS at baseline in the delivery group and controls was 19 (16-23) and 20 (13.25-27.75), and the median progression was 1 (0-3) and 0 (0-1) during the median 2.9-year follow-up, respectively. The median (Q1-Q3) SIJ score at baseline in the delivery group and controls was 13 (8-22) and 11 (6-22), and the median progression was 1.5 (0-3) and 1 (0-2), respectively. Using cut-off 0.5, 52.9, and 61.9% of r-axSpA patients and 39.3 and 44.4% of controls showed progression of whole spine and SIJs, respectively. However, no difference in proportion of spinal and SIJ progression and absolute score changes per time point was observed between two groups. Moreover, the SIJ score changes were comparable according to the delivery method.

Conclusion

Pregnancy and delivery do not affect the radiographic progression of the spine and SIJs in women with r-axSpA assessed by CT.

Can Bone Erosion in Axial Spondyloarthropathy be Detected by Ultrashort Echo Time Imaging? A Comparison With Computed Tomography in the Sacroiliac Joint

BACKGROUND

Structural lesion evaluation in axial spondyloarthropathy (SpA) can improve accuracy of diagnosis. However, structural lesions (bone erosions) are difficult to be assessed using conventional MRI compared to computed tomography (CT).

PURPOSE

To evaluate the diagnostic performance of ultrashort echo time (UTE) for detecting bone erosion in axial SpA compared to T1WI and three-dimensional double-echo steady-state (3D DESS) imaging using CT as the reference standard.

STUDY TYPE

Retrospective.

POPULATION

Fourteen patients (eight females, 57.1%) and 14 healthy controls (seven females, 50.0%) who underwent sacroiliac (SI) joint MRI and CT.

FIELD STRENGTH/SEQUENCE

3 T; TSE T1WI, 3D DESS, 2D UTE.

ASSESSMENT

The bilateral SI joints were assessed for bone erosion. Three observers scored bone erosion for all three sequences of MRI. CT was used as the gold standard. Diagnostic confidence in axial SpA was measured based on a four-point confidence score.

STATISTICAL TESTS

Correlation of erosion scores between CT and MRI were evaluated using Spearman's correlation test. Sensitivity, specificity, and positive-negative predictive values were calculated. Confidence scores were compared using the Wilcoxon sum rank test. Statistical significance was set at P < 0.05.

RESULTS

Compared with erosion scores of CT, the correlation coefficients for each MRI sequence showed significant low-to-high positive correlations (0.39-0.72). UTE imaging showed the highest correlation coefficients for all observers (0.70, 0.72, and 0.67, respectively). The specificity of UTE imaging was equal or higher than those of T1WI and 3D DESS for all observers (0.86 vs. 0.71 vs. 0.57; 0.93 vs. 0.71 vs. 0.57; 0.79 vs. 0.79 vs. 0.43). All observers had the highest confidence in interpreting UTE imaging for detecting bone erosion among the three sequences (3.5, 3.4, and 3.3 for UTE; 3.1, 3.0, and 2.6 for T1WI; and 3.2, 2.7, and 2.4 for DESS).

DATA CONCLUSION

UTE imaging can detect bone erosions in patients with axial SpA and show higher specificity than conventional T1WI and 3D DESS.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Use of Imaging in Axial Spondyloarthritis for Diagnosis and Assessment of Disease Remission in the Year 2022

Medical imaging remains the cornerstone of diagnostics and follow-up of axial spondyloarthritis (axSpA) patients. With the lack of specific biomarkers allowing monitoring of disease activity and progression, clinicians refer to imaging modalities for accurate evaluation of the axSpA burden. Technological advances and increasing availability of modern imaging techniques such as MRI have enabled faster diagnosis of the disease, hence dramatically changed the diagnostic delay and improved the prognosis and functional outcomes for axSpA patients.Active sacroiliitis as visualized by MRI has been widely accepted as a diagnostic tool, and definitions of inflammatory and structural lesions within the axial skeleton have been developed. Recently, it has been acknowledged that bone marrow edema, suggestive of sacroiliitis, is a common finding among non-SpA patients, and could be attributed to mechanical loading or accumulate with age in healthy individuals. Therefore, it is crucial to distinguish between true pathological and concealing imaging findings, not only for diagnostic but also for disease remission purposes. New imaging modalities, aimed for in vivo visualization of specific molecular processes, could be employed to cross-validate findings from techniques used in daily clinical practice. This review critically evaluates the use of different imaging modalities for diagnosis and assessment of disease remission in axSpA in the year 2022.

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.

The influence of age on the prevalence of inflammatory and structural MRI lesions in the SIJ of patients with and without axSpA

OBJECTIVE

To compare the influence of age on inflammatory (bone marrow oedema. BME) and structural (fat lesions (FL), erosions and ankylosis) MRI lesions in the SIJ of patients with and without axial spondyloarthritis (axSpA).

METHODS

In a retrospective study, SIJ MRI (STIR/T1 sequences) of consecutive patients with chronic back pain diagnosed with axSpA or non-SpA were evaluated based on SIJ quadrants (SIJ-Q). Two blinded readers evaluated BME and structural lesions. Reader agreement was evaluated for prevalence of MRI lesions related to age.

RESULTS

MRIs of 309 (175 axSpA, 134 non-SpA) patients were evaluated. Their mean age was 38.5 ± 11.4 vs 43.4 ± 13.8 years (y), 67% and 36% were male, CRP 1.6 ± 2.4 vs 1.1 ± 2.1 mg/dl, median symptom duration 48 and 60 months, respectively. SIJ-Q with BME and erosions were significantly more frequent in axSpA vs non-SpA patients independent of age, while this difference was seen for FL only in patients ≥50 y. The proportion of patients with ≥1 or ≥ 3 BME or chronic lesions except for FL increased with age in both groups, and was constantly higher in axSpA vs non-SpA. In univariate analyses, only female sex was significantly associated with more FL.

CONCLUSIONS

The proportion of patients with MRI lesions was high in both, axSpA and non-SpA patients. However, the prevalence of BME and erosions was significantly more frequent in patients with axSpA, was independent of age and also allowed for discrimination. FL occurred more frequently only in older age groups and were less reliable for discrimination vs. non-SpA patients.

Diagnostic evaluation of the sacroiliac joints for axial spondyloarthritis: should MRI replace radiography?

The possibility of detection of structural damage on magnetic resonance imaging (MRI) of sacroiliac joints raises the question of whether MRI can substitute radiographs for diagnostic evaluation and to a further extent for classification of axial spondyloarthritis (axSpA). In this viewpoint, we will argue that it is time to replace conventional radiographs with MRI for the assessment of structural changes in sacroiliac joints. This message is based on current data on the following questions: (1) How reliable are conventional radiographs in the diagnosis of axSpA overall and radiographic axSpA in particular? (2) How does T1-weighted MRI compare to radiographs in the detection of sacroiliitis? (3) Are there now other (better) MRI sequences than T1-weighted, which might be more suitable for the detection of structural lesions? (4) Which MRI sequences should be performed for the diagnostic evaluation of the sacroiliac joints? (5) Do we have data to define sacroiliitis based on structural changes detected by MRI?

Comparing MRI and conventional radiography for the detection of structural changes indicative of axial spondyloarthritis in the ASAS cohort

OBJECTIVES

To compare magnetic resonance imaging (MRI) and conventional radiography of sacroiliac joints (SIJs) for detection of structural lesions typical for axial spondyloarthritis (axSpA).

METHODS

Adult patients from the Assessment of SpondyloArthritis international Society (ASAS) cohort with symptoms suggestive of axSpA and both SIJ MRIs and radiographs available for central reading were included. Radiographs were evaluated by three readers according to the modified New York (mNY) criteria grading system. The presence of structural damage on radiographs was defined as 1) fulfilment of the radiographic mNY criterion and 2) additionally, a lower threshold for sacroiliitis of at least grade 2 unilaterally. MRI scans were assessed for the presence of structural changes indicative of axSpA by 7 readers. Diagnostic performance (sensitivity-Se, specificity-Sp, positive and negative predictive values-PPV and NPV-and positive and negative likelihood ratios-LR+ and LR-) of MRI and radiographs (vs rheumatologist's diagnosis of axSpA) were calculated.

RESULTS

Overall, 183 patients were included, 135 (73.7%) were diagnosed with axSpA. Structural lesions indicative of axSpA on MRI had Se 38.5%, Sp 91.7%, PPV 92.9%, NPV 34.6%, LR + 4.62, LR- 0.67. Sacroiliitis according to the mNY criteria had Se 54.8%, Sp 70.8%, PPV 84.1%, NPV 35.8%, positive LR + 1.88, LR- 0.64. Radiographic sacroiliitis of at least grade 2 unilaterally had Sn 65.2%, Sp 50.0%, PPV 78.6%, NPV 33.8%, LR + 1.30, LR- 0.69.

CONCLUSION

Structural lesions of SIJ detected by MRI demonstrated better diagnostic performance and better inter-reader reliability compared with conventional radiography.

The frequency of sacroiliitis on MRI in subjects over 55 years of age

OBJECTIVE

To evaluate the frequency of sacroiliitis in older subjects.

MATERIALS AND METHODS

Consecutive MRI examinations of the sacroiliac joints (SIJs) performed for suspected sacroiliitis (2005-2019) in patients ≥ 18 years were retrospectively evaluated for the presence of active/structural lesions and were categorized for the presence/absence of sacroiliitis. Clinical and imaging parameters were compared between subjects with sacroiliitis according to age groups < 40 years, 40-55, and > 55 years. Clinical parameters including inflammatory back pain (IBP) and other spondyloarthritis (SpA) features were retrieved from the medical records.

RESULTS

A total of 431 patients with SIJs MRI were evaluated: median age, 44 [IQR 35-54]; female:male 267(62%):164(38%). Sacroiliitis was diagnosed in 89 (20.6%) subjects-median age, 41 years [IQR 32-54], 52% females- and was equally prevalent among the different age groups: > 40 years old, 23.6%; 40-55, 20%; and > 55 years old, 17%, p = 0.43, with active/structural lesions equally dispersed. Older patients (> 55) started suffering from back pain at an older age and had a longer delay in diagnosis. Gender distribution, the presence of IBP, and other SpA features were no different in patients < 45 and > 55 years of age.

CONCLUSIONS

The frequency of sacroiliitis on SIJs-MRI in subjects > 55 years is similar to its frequency in younger subjects and is associated with the same type and magnitude of active and structural MRI lesions. Clinical parameters such as IBP and additional SpA features are similarly prevalent in older and younger subjects suggesting they suffer from the same disease and differing only in age of presentation.

Novel imaging techniques for sacroiliac joint assessment

PURPOSE OF REVIEW

Imaging of the sacroiliac joints is one of the cornerstones in the diagnosis and monitoring of axial spondyloarthritis. We aim to present an overview of the emerging imaging techniques for sacroiliac joint assessment and provide an insight into their relevant benefits and pitfalls.

RECENT FINDINGS

Evaluation of structural and active inflammatory lesions in sacroiliitis are both important for understanding the disease process. Dual-energy computed tomography (CT) can detect inflammatory bone marrow edema in the sacroiliac joints and provides an alternative for magnetic resonance imaging (MRI). Three-dimensional gradient echo sequences improve the visualization of erosions on MRI. Susceptibility weighted MRI and deep learning-based synthetic CT are innovative MRI techniques that allow for generating 'CT-like' images and better depict osseous structural lesions than routine MRI sequences.

SUMMARY

New imaging innovations and developments result in significant improvements in the imaging of spondyloarthritis. Advanced MRI techniques enhance its potential for the accurate detection of structural and active inflammatory lesions of sacroiliitis in one single imaging session.

Future of Low-Dose Computed Tomography and Dual-Energy Computed Tomography in Axial Spondyloarthritis

Purpose of Review

Recent technical advances in computed tomography (CT) such as low-dose CT and dual-energy techniques open new applications for this imaging modality in clinical practice and for research purposes. This article will discuss the latest innovations and give a perspective on future developments.

Recent Findings

Low-dose CT has increasingly been used for assessing structural changes at the sacroiliac joints and the spine. It has developed into a method with similar or even lower radiation exposure than radiography while outperforming radiography for lesion detection. Despite being incompatible with low-dose scanning, some studies have shown that dual-energy CT can provide additional information that is otherwise only assessable with magnetic resonance imaging (MRI). However, it is unclear whether this additional information is reliable enough and if it would justify the additional radiation exposure, i.e. whether the performance of dual-energy CT is close enough to MRI to replace it in clinical practice.

Summary

While the role of dual-energy CT in patients with axial spondyloarthritis remains to be established, low-dose CT has developed to an appropriate modality that should replace radiography in many circumstances and might supplement MRI.

Clinical characteristics, treatment and outcomes of acute postpartum inflammatory sacroiliitis: a retrospective study

PURPOSE

We performed this research to report the clinical characteristics and clinical therapeutic strategies of acute postpartum inflammatory sacroiliitis.

METHODS

We retrospectively analyzed the data of patients diagnosed with acute postpartum inflammatory sacroiliitis from 2014 to 2020. All their clinical details including clinical symptoms and signs, laboratory tests, radiologic examination, diagnosis and treatment process and clinical outcomes were obtained and analyzed in this retrospective analysis.

RESULTS

Eleven patients diagnosed with acute postpartum inflammatory sacroiliitis complain of low back pain. Magnetic resonance imaging (MRI) is useful in diagnosing acute postpartum inflammatory sacroiliitis. The systemic non-steroidal anti-inflammatory drugs (NSAIDs) administration, sacroiliac joint injection, and physical therapy effectively alleviated the pain with symptoms disappearing, and the abnormal signal reduced in MRI.

CONCLUSION

Acute postpartum inflammatory sacroiliitis is an uncommon disease with atypical symptoms. MRI examination may be the best diagnostic method. General NSAIDs and sacroiliac joint injections of local anesthetic plus corticosteroid under the guidance of fluoroscopy or ultrasound can achieve safe and effective treatment. This retrospective study was approved by the Committee on the Ethics of our hospital (No. 202101023).

TRIAL REGISTRY

Trial registration was performed in the Chinese Clinical Trial Registry ( http://www.chictr.org.cn , No. ChiCTR2100045656).

Bone Involvement in Patients with Spondyloarthropathies

Spondyloarthropathies (SpA) are common systemic inflammatory rheumatic diseases, in which, as in other rheumatic diseases, levels of markers of bone resorption are elevated, leading to bone loss and elevated risk of vertebral fractures. However, the diseases are also associated with new bone formation in the spine, the so-called syndesmophytes. We tried to unravel the pathogenesis of formation and growth of syndesmophytes and evaluated new diagnostic and treatment options. After a successful meeting of the Working Group on Rheumatic Diseases at the ECTS 2020, we (WL and CR) were excited about the quality of the speakers (CM, JH, AG, and GL) and their complimentary lectures. Given the relative lack of reviews on spondyloarthropathies and bone, we decided to work together on a comprehensive review that might be interesting for basic scientists and clinically relevant for clinicians. Radiographic progression in axSpA is linked to several risk factors, like male sex, smoking, HLA-B-27, increased levels of CRP, presence of syndesmophytes, and marked inflammation on MRI. The potential role of mechanical stress in the context of physically demanding jobs has been also suggested to promote structural damages. Different treatment options from NSAIDs to biologic agents like TNF inhibitors (TNFi) or IL-17inhibitors (IL-17i) result in a reduction of inflammation and symptoms. However, all these different treatment options failed to show clear and reproducible results on inhibition on syndesmophyte formation. The majority of data are available on TNFi, and some studies suggested an effect in subgroups of patients with ankylosing spondylitis. Less information is available on NSAIDs and IL-17i. Since IL-17i have been introduced quite recently, more studies are expected. IL-17 inhibitors (Il-17i) potently reduce signs and symptoms, but serum level of IL-17 is not elevated, therefore, IL-17 probably has mainly a local effect. The failure of anti-IL-23 in axSpA suggests that IL-17A production could be independent from IL-23. It may be upregulated by TNFα, resulting in lower expression of DKK1 and RANKL and an increase in osteogenesis. In active AS markers of bone resorption are increased, while bone formation markers can be increased or decreased. Bone Turnover markers and additional markers related to Wnt such as DKK1, sclerostin, and RANKL are valuable for elucidating bone metabolism on a group level and they are not (yet) able to predict individual patient outcomes. The gold standard for detection of structural lesions in clinical practice is the use of conventional radiographics. However, the resolution is low compared to the change over time and the interval for detecting changes are 2 years or more. Modern techniques offer substantial advantages such as the early detection of bone marrow edema with MRI, the fivefold increased detection rate of new or growing syndesmophytes with low-dose CT, and the decrease in 18F-fluoride uptake during treatment with TNFα-inhibitors (TNFi) in a pilot study in 12 AS patients. Detection of bone involvement by new techniques, such as low-dose CT, MRI and 18-Fluoride PET-scans, and bone turnover markers, in combination with focusing on high-risk groups such as patients with early disease, elevated CRP, syndesmophytes at baseline, male patients and patients with HLA-B27 + are promising options for the near future. However, for optimal prevention of formation of syndesmophytes we need more detailed insight in the pathogenesis of bone formation in axSpA and probably more targeted therapies.

Selection of X-ray versus magnetic resonance imaging as a first-line imaging modality for diagnosing axial spondyloarthritis

Introduction:

To determine the cut-off values for age and symptom duration that could be used in selecting preferential first-line imaging modality of sacroiliac joints [X-ray versus magnetic resonance imaging (MRI)] for diagnosing axial spondyloarthritis (axSpA).

Methods:

This retrospective cohort study included 388 patients newly diagnosed with axSpA. Patients were classified into radiographic axSpA (n = 322) and non-radiographic axSpA (n = 66) groups according to the fulfilment of modified New York criteria by X-ray. Patient characteristics of the two groups were compared. Receiver operating characteristic (ROC) curve analysis was conducted to determine the cut-off values for age and symptom duration that best distinguish non-radiographic axSpA from radiographic axSpA.

Results:

Compared with patients with radiographic axSpA, those with non-radiographic axSpA were younger at diagnosis (35.7 ± 11.3 years versus 26.8 ± 7.8 years, p < 0.001) and had shorter symptom duration [5.1 (2.1–12.0) years versus 1.0 (0.5–3.2) years, p < 0.001]. ROC analysis showed that age > 33.5 years at diagnosis [area under the curve (AUC): 0.734] and symptom duration > 4.1 years (AUC: 0.787) were the cut-off values that best discriminate radiographic axSpA from non-radiographic axSpA.

Conclusion:

The best cut-off values for age and symptom duration for predicting radiographic sacroiliitis are 33.5 and 4.1 years, respectively. It is reasonable to use X-ray as a first-line imaging modality in patients older than 33.5 years with a symptom duration longer than 4.1 years, and use MRI as a first-line imaging in patients younger than 33.5 years with a symptom duration less than 4.1 years.

What amount of structural damage defines sacroiliitis: a CT study

OBJECTIVES

To propose a data-driven definition for structural changes of sacroiliac (SI) joints in the context of axial spondyloarthritis (axSpA) imaging on a large collective of CT datasets.

METHODS

546 individuals (102 axSpA, 80 non-axSpA low back pain and 364 controls without back pain) with SI joint CTs were evaluated for erosions, sclerosis and ankylosis using a structured scoring system. Lesion frequencies and spatial distribution were compared between groups. Diagnostic performance (sensitivity (SE), specificity (SP), positive predictive values, negative predictive values and positive and negative likelihood ratios) was calculated for different combinations of imaging findings. Clinical diagnosis served as standard of reference.

RESULTS

Ankylosis and/or erosions of the middle and dorsal joint portions yielded the best diagnostic performance with SE 67.6% and SP 96.3%. Inclusion of ventral erosions and sclerosis resulted in lower diagnostic performance with SE 71.2%/SP 92.5% and SE 70.6%/SP 90.0%, respectively.

CONCLUSIONS

Sclerosis and ventrally located erosions of SI joints have lower specificity on CT of the SI joint in the context of axSpA imaging. Ankylosis and/or erosions of the middle and dorsal joint portions show a strong diagnostic performance and are appropriate markers of a positive SI joint by CT.

Magnetic Resonance Imaging Versus Computed Tomography for Three-Dimensional Bone Imaging of Musculoskeletal Pathologies: A Review

Magnetic resonance imaging (MRI) is increasingly utilized as a radiation‐free alternative to computed tomography (CT) for the diagnosis and treatment planning of musculoskeletal pathologies. MR imaging of hard tissues such as cortical bone remains challenging due to their low proton density and short transverse relaxation times, rendering bone tissues as nonspecific low signal structures on MR images obtained from most sequences. Developments in MR image acquisition and post‐processing have opened the path for enhanced MR‐based bone visualization aiming to provide a CT‐like contrast and, as such, ease clinical interpretation. The purpose of this review is to provide an overview of studies comparing MR and CT imaging for diagnostic and treatment planning purposes in orthopedic care, with a special focus on selective bone visualization, bone segmentation, and three‐dimensional (3D) modeling. This review discusses conventional gradient‐echo derived techniques as well as dedicated short echo time acquisition techniques and post‐processing techniques, including the generation of synthetic CT, in the context of 3D and specific bone visualization. Based on the reviewed literature, it may be concluded that the recent developments in MRI‐based bone visualization are promising. MRI alone provides valuable information on both bone and soft tissues for a broad range of applications including diagnostics, 3D modeling, and treatment planning in multiple anatomical regions, including the skull, spine, shoulder, pelvis, and long bones.

Addition of CT to Improve the Diagnostic Confidence for the Detection of Sacroiliac Joint Erosions in Patients with Equivocal MRI Findings

PURPOSE

To determine if CT can improve the diagnostic confidence for the detection of sacroiliac joint (SIJ) erosions in patients with equivocal MRI findings.

METHODS

A retrospective analysis of adult patients who had an SIJ MRI and a subsequent SIJ CT within 12 months was conducted. Using a 5-point Likert scale, two reviewers evaluated the de-identified MRI and CT images in randomized order and in separate sessions to answer the question: "Does the patient have SIJ erosions?". A Fisher's exact test was used to analyze the difference in diagnostic confidence, and intraclass correlation coefficient (ICC) was used to determine interrater reliability.

RESULTS

54 patients were included in the analysis (average age, 43.9 years). The average time interval between initial SIJ MRI and subsequent CT was 14.4 weeks (range, 5.6-50.3 weeks). CT resulted in significantly more cases with definitive diagnostic confidence than cases with probable or equivocal confidence compared to MRI (P < .001). Amongst cases with equivocal findings on MRI, 73.2% of cases had definitive diagnoses on CT. There was moderate interrater agreement for MRI, with an ICC of .490 [95% CI, .258-.669], and excellent agreement for CT, with an ICC of .832 [95% CI, .728-.899].

CONCLUSION

Overall, CT led to significantly increased diagnostic confidence and higher interrater reliability for the detection of SIJ erosions compared to MRI. Judicious use of CT may be useful in detecting SIJ erosions in patients with equivocal MRI findings.

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.

New Perspectives on Diagnosing Psoriatic Arthritis by Imaging Techniques

Psoriatic arthritis is a chronic inflammatory condition that can lead to severe functional impairment and irreversible damage. The diagnosis can be difficult in early cases where the clinical exam is often scarce. The lack of a serological biomarker can lead to a considerable delay in diagnosis. In this review, we discuss the existent imaging methods that have improved the diagnosis of psoriatic arthritis (PsA). The degree and type of musculoskeletal involvement cannot be assessed by only one imaging method. We think that a combination of methods is the best approach to evaluate both structural damage and inflammatory lesions and that ultrasound (US) could be the best tool to screen a patient when considering the diagnosis of PsA. US is an accessible, non-ionizing technique that offers information regarding active inflammation in joints, entheses, and soft tissues.

ACR Appropriateness Criteria® Inflammatory Back Pain: Known or Suspected Axial Spondyloarthritis: 2021 Update

Inflammatory back pain is a hallmark feature of axial spondyloarthritis, a heterogeneous group of inflammatory disorders which affects the sacroiliac joints and spine. Imaging plays a key role in diagnosis of this disease and in facilitating appropriate treatment. This document provides evidence-based recommendations on the appropriate use of imaging studies during multiple stages of the clinical evaluation of patients with suspected or known axial spondyloarthritis. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Significance of structural changes in the sacroiliac joints of patients with axial spondyloarthritis detected by MRI related to patients symptoms and functioning

Axial spondyloarthritis (axSpA) is a chronic inflammatory rheumatic disease that manifests primarily in the axial skeleton, initially mostly in the sacroiliac joints (SIJ), usually later spreading to the spine. The disease is characterised by inflammation and new bone formation which are mainly assessed by conventional radiography (CR) and magnetic resonance imaging (MRI). Tumour necrosis factor inhibitors (TNFi) and interleukin-17 antagonists have been shown to be efficacious and efficient in patients with axSpA. This treatment seems to also inhibit structural damage, for example, retard radiographic progression. Indeed, a reduction of new bone formation in the spine, as assessed by CR, has been reported to occur after at least 2 years of therapy with TNFi. Recently, a reduction of erosions and ankylosis in the SIJ has also been observed in axSpA patients treated with etanercept and filgotinib. In this narrative review, we discuss the limited significance of such findings.

Successful Diagnosis of Sacroiliac Joint Dysfunction

Background

Sacroiliac joint (SIJ) pain is one of the most common causes of low back pain, accounting for 15 to 30% of all cases. Although SIJ dysfunction accounts for a large portion of chronic low back pain prevalence, it is often overlooked or under diagnosed and subsequently under treated. The purpose of this review was to establish a best practices model to effectively diagnose SIJ pain through detailed history, physical exam, review of imaging, and diagnostic block.

Methods

A literature search was performed on the diagnosis of sacroiliac joint pain and sacroiliac joint dysfunction. The authors proposed diagnostic recommendations based upon the available literature and a detailed understanding of diagnosing SIJ pain.

Results

The practitioner must focus on the history, location of pain, observed gait pattern, and perform key points of the physical exam including sacroiliac provocative maneuvers. If the patient exhibits at least three provocative maneuvers then the SIJ may be considered as a possible source of pain. Additionally, a thorough review of the imaging should be performed to rule out other etiologies of low back pain. In the absence of any pathognomonic tests or examination findings, diagnostic SIJ blocks have evolved as the diagnostic standard.

Conclusion

The diagnosis of SIJ pain is a multifaceted process that involves a careful assessment including differentiating other pain generators in the region. This involves careful history taking, appropriate physical examination including provocative maneuvers and diagnostic injections. Once the diagnosis is confirmed, long-term solutions may be considered, including recent advances in sacral lateral branch denervation and sacroiliac joint fusion.