Imaging of sacroiliitis: Current status, limitations and pitfalls

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.

MR Imaging Approach to Arthritides and Spondyloarthropathies

MR imaging is a valuable imaging tool in the assessment of spinal arthritides, allowing the radiologist to formulate a rational differential diagnosis and construct a meaningful radiologic report. Of this, spondyloarthritis has garnered the most attention over the years given its debilitating symptoms and disabling effect. MR imaging depicts both inflammatory and structural lesions in the spine and SI joints and a systematic anatomic approach in appraising these lesions can aid in proper diagnosis. Combined with careful correlation with clinical findings and biomarkers, MR imaging is an instrumental tool in the diagnosis and treatment planning of spinal arthritides, particularly spondyloarthritis.

Sacroiliitis: current imaging modalities and future directions: a narrative review

Sacroiliitis, or inflammation of one or both of the sacroiliac joints (SIJs), can be difficult to distinguish from other etiologies of lower back and buttock pain due to diverse patient presentations and a lack of highly sensitive and specific diagnostic modalities. Although physical examination, provocation tests, and an SIJ block test are informative, confirmatory imaging is often required to improve diagnostic accuracy. Radiography and magnetic resonance imaging (MRI) are the most popular imaging studies for this purpose, but other modalities such as computed tomography (CT), single-photon emission computed tomography (SPECT)/CT, positron emission tomography (PET)/CT, and ultrasonography are emerging as viable alternatives. This narrative review provides a comprehensive summary of the history, clinical use and limitations of each imaging modality in the diagnosis of sacroiliitis. Novel techniques in image acquisition and analysis, such as digital tomosynthesis (DT), volumetric interpolated breath-hold examination (VIBE) MRI and dual energy CT (DECT) are also discussed.

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.

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.

Sacroiliac Joint: Function, Pathology, Treatment, and Contribution to Outcomes in Spine and Hip Surgery

➢ Low back pain has a lifetime incidence of up to 84% and represents the leading cause of disability in the United States; 10% to 38% of cases can be attributed to sacroiliac joint (SIJ) dysfunction as an important pain generator.➢ Physical examination of the SIJ, including >1 provocation test (due to their moderate sensitivity and specificity) and examination of adjacent joints (hip and lumbar spine) should be routinely performed in all patients presenting with low back, gluteal, and posterior hip pain.➢ Radiographic investigations including radiographs, computed tomography, and magnetic resonance imaging with protocols optimized for the visualization of the SIJs may facilitate the diagnosis of common pathologies.➢ Intra-articular injections with anesthetic can be helpful in localizing the source of low back pain. Over-the-counter analgesics, physiotherapy, intra-articular injections, radiofrequency ablation, and surgery are all management options and should be approached from the least invasive to the most invasive to minimize the risks of complications.➢ Lumbar fusion surgery predisposes patients to more rapid SIJ degeneration and can also result in more rapid degenerative changes in the hip joints, especially with SIJ fusion.➢ Hip surgery, including hip arthroplasty and preservation surgery, is not a risk factor for SIJ degeneration, although reduced outcomes following hip surgery can be seen in patients with degenerative SIJ changes.

Postpartum Septic Osteoarthritis: A case series study

Introduction-Aim: Postpartum septic osteoarthritis is a rare but serious condition often misdiagnosed due to overlap with common postpartum symptoms like pelvic pain and joint stiffness. This case series aims to describe the clinical, bacteriological, and radiological characteristics of postpartum septic osteoarthritis, as well as the treatment approaches and patient outcomes. Methods: A retrospective case series was conducted at Farhat Hached University Hospital, from 2006 to 2022, involving patients with confirmed postpartum septic osteoarthritis. Clinical data, laboratory findings, imaging results, treatments, and outcomes were analyzed Results: The mean age of the seven patients was 31.4 years. All patients presented with joint pain, with fever and functional impairment where each was observed in 85.7% of cases. The average diagnostic delay was 17 days. MRI findings revealed bone marrow edema in all patients, Abscesses in 28.5% of cases, periarticular soft tissue edema, and intra-articular effusions in 71.4% of cases. The pubic symphysis was the most commonly affected site (57.1%), followed by the sacroiliac joints (28.6%). Only one pathogen, Streptococcus pyogenes, was isolated. Nearly all patients received dual antibiotic therapy for an average duration of 4 to 6 weeks. Satisfactory clinical progress without sequelae was noted and maintained after an average follow-up of 5 to 6 months. .Conclusion: Our results revealed that postpartum septic osteoarthritis requires prompt diagnosis and early treatment to prevent severe complications. MRI plays a critical role in early detection, while timely antibiotic therapy leads to favorable long-term outcomes.

Single-Centre Analysis of Magnetic Resonance Imaging of Sacroiliac Joints in a Paediatric Population

Background: Sacroiliitis in children is usually connected with one of the subtypes of juvenile idiopathic arthritis (JIA), such as enthesitis-related arthritis, psoriatic arthritis, or undifferentiated arthritis. The main diagnostic method is magnetic resonance imaging (MRI) of the sacroiliac joints, which can reveal bone marrow edema (BME) as a sign of an active inflammation process. This research aimed to retrospectively investigate the associations between the clinical presentation, laboratory test results, and MRI results of the sacroiliac joints of children. Methods: A total of 152 paediatric patients who underwent MRI of the sacroiliac joints were included in this single-centre study. The mean age of patients was 13.91 ± 2.97, while the female-to-male ratio was 1.36:1. JIA diagnosis was confirmed in 91 (59.87%) patients. Results: The main symptom reported by 128 (83.21%) patients was chronic pain, while in another 40 (31.25%) patients, it was chronic back pain. Patients with arthritis and BME in the sacroiliac joints were more likely to report chronic back pain, while patients with JIA but without BME in the sacroiliac joints were often positive for anti-nuclear antibodies (ANA). The widening of any joint contour was observed in 43 (28.29%) patients, and reduced joint mobility was observed in 61 (40.13%). Elevation of inflammatory blood parameters occurred in 31 (20.39%) patients, but this was not statistically related to BME presence in the sacroiliac joints. Radiological findings included BME (n = 36; 23.68% of examinations), joint space narrowing (n = 10; 27.78% of examinations), erosions (n = 7; 19.44% of examinations), and joint fluid (n = 7; 19.44% of examinations). There was a statistically significant relationship between the presence of BME in the sacroiliac joints and all of the above radiological findings. Conclusions: The radiological findings of MRI of the sacroiliac joints are significantly statistically related to chronic back pain in patients, while there is no relationship between any inflammatory blood parameter and the presence of BME.

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

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

Association between serum interleukin-17 levels and ectopic bone formation in OPLL patients with DISH

OBJECTIVE

To investigate the relationship between the severity and morphology of heterotopic ossification in the spinal ligaments including sacroiliac (SI) joints, and serum interleukin-17 (IL-17) levels in patients with ossification of the posterior longitudinal ligament (OPLL) with or without diffuse idiopathic skeletal hyperostosis (DISH), as well as a non-OPLL group.

METHODS

A total of 103 patients with OPLL [DISH (-), n = 50; DISH (+), n = 53] and 53 age- and gender-matched controls were included. The serum levels of IL-17 were analysed, and the severity of ectopic ossification and the morphology of ectopic bone formation were evaluated. The SI joint morphological variations were categorized into four types.

RESULTS

No significant differences were found in serum IL-17 levels between the OPLL and control groups. However, the DISH (+) group showed higher IL-17 levels than the DISH (-) group, especially in female patients (P = 0.003). Additionally, IL-17 levels were positively correlated with the number of flat vertebral units, this being one of the characteristic DISH ossification types (R2 = 0.199, P = 0.012). IL-17 levels in the type showing bridging osteophyte and bone fusion were significantly higher in the DISH (+) group than in the DISH (-) group.

CONCLUSION

The morphological characteristics of paravertebral bone formation in the entire spine, including the SI joint, are likely associated with serum IL-17 levels in OPLL. These findings provide pathological and serological evidence of local inflammation contributing to paravertebral ossification of OPLL patients.

Chronic Low Back Pain: History, Symptoms, Pain Mechanisms, and Treatment

Chronic low back pain (cLBP) is the most frequently reported cause of years lived with disability. Identifying the anatomical structures or dysfunction contributing to patients' symptoms is critical to guiding treatment. The etiology of back pain and differential diagnosis is often broad, ranging from non-degenerative cLBP (trauma, tumor, inflammation, infection, etc.) to degenerative (also described as nonspecific) cLBP. After eliminating suspicion for more insidious causes of cLBP, a thorough investigation can be conducted in an attempt to identify a source of degenerative cLBP. Degenerative cLBP can originate from many sources, and a detailed understanding of the structures potentially involved is invaluable for an accurate diagnosis. This review article aims to provide a broad overview of the utility of clinical history, physical exam findings, imaging findings, and diagnostic procedures in identifying the cause of patients' cLBP. We provide a framework to help guide clinicians by dividing the structures into groups as follows: anterior vertebral column, posterior vertebral column, and extra-vertebral pain. For each condition listed, we touch on the treatment options that can be considered.

Radiological Insights into Sacroiliitis: A Narrative Review

Sacroiliitis is the inflammation of the sacroiliac joint, the largest axial joint in the human body, contributing to 25% of lower back pain cases. It can be detected using various imaging techniques like radiography, MRI, and CT scans. Treatments range from conservative methods to invasive procedures. Recent advancements in artificial intelligence offer precise detection of this condition through imaging. Treatment options range from physical therapy and medications to invasive methods like joint injections and surgery. Future management looks promising with advanced imaging, regenerative medicine, and biologic therapies, especially for conditions like ankylosing spondylitis. We conducted a review on sacroiliitis using imaging data from sources like PubMed and Scopus. Only English studies focusing on sacroiliitis's radiological aspects were included. The findings were organized and presented narratively.

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.

Performance of Fully Automated Algorithm Detecting Bone Marrow Edema in Sacroiliac Joints

This study evaluates the performance of a fully automated algorithm to detect active inflammation in the form of bone marrow edema (BME) in iliac and sacral bones, depending on the quality of the coronal oblique plane in patients with axial spondyloarthritis (axSpA). The results were assessed based on the technical correctness of MRI examination of the sacroiliac joints (SIJs). A total of 173 patients with suspected axSpA were included in the study. In order to verify the correctness of the MRI, a deviation angle was measured on the slice acquired in the sagittal plane in the T2-weighted sequence. This angle was located between the line drawn between the posterior edges of S1 and S2 vertebrae and the line that marks the actual plane in which the slices were acquired in T1 and STIR sequences. All examinations were divided into quartiles according to the deviation angle measured in degrees as follows: 1st group [0; 2.2], 2nd group (2.2; 5.7], 3rd group (5.7; 10] and 4th group (10; 29.2]. Segmentations of the sacral and iliac bones were acquired manually and automatically using the fully automated algorithm on the T1 sequence. The Dice coefficient for automated bone segmentations with respect to reference manual segmentations was 0.9820 (95% CI [0.9804, 0.9835]). Examinations of BME lesions were assessed using the SPARCC scale (in 68 cases SPARCC > 0). Manual and automatic segmentations of the lesions were performed on STIR sequences and compared. The sensitivity of detection of BME ranged from 0.58 (group 1) to 0.83 (group 2) versus 0.76 (total), while the specificity was equal to 0.97 in each group. The study indicates that the performance of the algorithm is satisfactory regardless of the deviation angle.

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.

Role of advanced MRI techniques for sacroiliitis assessment and quantification

The introduction of MRI was supposed to be a qualitative leap for the evaluation of Sacroiliac Joint (SIJ) in patients with Axial Spondyloarthropathies (AS). In fact, MRI findings such as bone marrow edema around the SIJ has been incorporated into the Assessment in SpondyloArthritis International Society (ASAS criteria). However, in the era of functional imaging, a qualitative approach to SIJ by means of conventional MRI seems insufficient. Advanced MRI sequences, which have successfully been applied in other anatomical areas, are demonstrating their potential utility for a more precise assessment of SIJ. Dixon sequences, T2-mapping, Diffusion Weighted Imaging or DCE-MRI can be properly acquired in the SIJ with promising and robust results. The main advantage of these sequences resides in their capability to provide quantifiable parameters that can be used for diagnosis of AS, surveillance or treatment follow-up. Further studies are needed to determine if these parameters can also be integrated into ASAS criteria for reaching a more precise classification of AS based not only on visual assessment of SIJ but also on measurable data.

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.

Common incidental findings on sacroiliac joint MRI: Added value of MRI-based synthetic CT

PURPOSE

To determine the prevalence of incidental findings on sacroiliac joint MRI and to determine the added value of MRI-based synthetic CT in the detection and evaluation of these incidental findings.

METHOD

In this retrospective study 210 patients clinically suspected of spondyloarthritis who underwent MRI of the sacroiliac joint with synthetic CT sequence were included. The images were reviewed by two radiologists in consensus for the prevalence of sacroiliitis, incidental findings, and the ability of synthetic CT and the conventional MRI to detect and diagnose these findings.

RESULTS

In 44.7% of patients sacroiliitis was present. In 89.0% of patients MRI showed at least one incidental finding other than sacroiliitis. Degeneration of the sacroiliac joint was the most prevalent finding (140 patients, 66.6%). The most frequent incidental findings outside the sacroiliac joint were facet joint degeneration (29.0%), disc degeneration (25.2%), enostosis (19.5%) and lumbosacral transitional vertebrae (14.3%). A total of 788 lesions was recorded and synthetic CT was found to be problem solving or necessary for diagnosis in 543 (68.9%) of these lesions. 42.1% of lesions were not visible on conventional MRI (T1 TSE and STIR), most often degenerative osteophytes in the sacroiliac joint or lower lumbar spine.

CONCLUSION

Incidental findings are seen more frequently on sacroiliac joint MRI than sacroiliitis, which is relevant as some will have clinical significance or require treatment. Nearly half of these incidental lesions were only visible on synthetic CT, which additionally has been shown to be problem solving for diagnosis in many other cases.

Exploration of the shared pathways and common biomarker PAN3 in ankylosing spondylitis and ulcerative colitis using integrated bioinformatics analysis

Background

Ulcerative colitis (UC) is a chronic autoimmune-related disease that causes inflammation of the intestine. Ankylosing spondylitis (AS) is a common extraintestinal complication of UC involving the sacroiliac joint. However, the pathogenesis of AS secondary to UC has not been studied. This study aimed to investigate the shared pathways and potential common biomarkers of UC and AS.

Methods

Microarray data downloaded from the Gene Expression Omnibus (GEO) database were used to screen differentially expressed genes (DEGs) in the UC and AS datasets. Weighted gene co-expression network analysis (WGCNA) was performed to identify co-expression modules related to UC and AS. Shared genes were then further analyzed for functional pathway enrichment. Next, the optimal common biomarker was selected using SVM-RFF and further validated using two independent GEO datasets. Finally, immune infiltration analysis was used to investigate the correlation of immune cell infiltration with common biomarkers in UC and AS.

Results

A total of 4428 and 2438 DEGs in UC and AS, respectively, were screened. Four modules were identified as significant for UC and AS using WGCNA. A total of 25 genes overlapped with the strongest positive and negative modules of UC and AS. KEGG analysis showed these genes may be involved in the mitogen-activated protein kinase (MAPK) signaling pathway. GO analysis indicated that these genes were significantly enriched for RNA localization. PAN3 was selected as the optimal common biomarker for UC and AS. Immune infiltration analysis showed that the expression of PAN3 was correlated with changes in immune cells.

Conclusion

This study first explored the common pathways and genetic diagnostic markers involved in UC and AS using bioinformatic analysis. Results suggest that the MAPK signaling pathway may be associated with both pathogeneses and that PAN3 may be a potential diagnostic marker for patients with UC complicated by AS.

The American Society of Pain and Neuroscience (ASPN) Evidence-Based Clinical Guideline of Interventional Treatments for Low Back Pain

Introduction

Painful lumbar spinal disorders represent a leading cause of disability in the US and worldwide. Interventional treatments for lumbar disorders are an effective treatment for the pain and disability from low back pain. Although many established and emerging interventional procedures are currently available, there exists a need for a defined guideline for their appropriateness, effectiveness, and safety.

Objective

The ASPN Back Guideline was developed to provide clinicians the most comprehensive review of interventional treatments for lower back disorders. Clinicians should utilize the ASPN Back Guideline to evaluate the quality of the literature, safety, and efficacy of interventional treatments for lower back disorders.

Methods

The American Society of Pain and Neuroscience (ASPN) identified an educational need for a comprehensive clinical guideline to provide evidence-based recommendations. Experts from the fields of Anesthesiology, Physiatry, Neurology, Neurosurgery, Radiology, and Pain Psychology developed the ASPN Back Guideline. The world literature in English was searched using Medline, EMBASE, Cochrane CENTRAL, BioMed Central, Web of Science, Google Scholar, PubMed, Current Contents Connect, Scopus, and meeting abstracts to identify and compile the evidence (per section) for back-related pain. Search words were selected based upon the section represented. Identified peer-reviewed literature was critiqued using United States Preventive Services Task Force (USPSTF) criteria and consensus points are presented.

Results

After a comprehensive review and analysis of the available evidence, the ASPN Back Guideline group was able to rate the literature and provide therapy grades to each of the most commonly available interventional treatments for low back pain.

Conclusion

The ASPN Back Guideline represents the first comprehensive analysis and grading of the existing and emerging interventional treatments available for low back pain. This will be a living document which will be periodically updated to the current standard of care based on the available evidence within peer-reviewed literature.

Water Fraction Ratio of the Sacroiliac Joint Subchondral Bone Marrow in Patients with Ankylosing Spondylitis Predicts the Degree of Disease Activity

Objectives: Ankylosing spondylitis (AS) is a chronic inflammatory arthritis with characteristic involvement of the spine and sacroiliac joints. MRI may be the only indicator of disease activity or response. This study aimed to use a novel water fraction measurement technique on MRI as a biomarker to predict disease activity in patients with AS. Methods: We enrolled 39 patients (18 men [mean age, 38.6 years; range, 18−59 years] and 21 women [mean age, 39.3 years; range, 23−61 years]) who were clinically diagnosed with AS and underwent MRI, including mDixon sequences. Water fraction values of sacroiliac joint subchondral bone marrow were derived from the mDixon sequences. The Ankylosing Spondylitis Disease Activity Score (ASDAS) was recorded using clinical information and laboratory values from medical records. Multiple linear regression, Firth logistic regression, and intraclass correlation coefficients were used for the statistical analysis. Results: In multiple linear regression, water fraction, subchondral bone marrow edema, subchondral bone erosion, and subchondral bone marrow enhancements were significantly associated with ASDAS with C-reactive protein (ASDAS-CRP). The water fraction parameters showed a good linear correlation with ASDAS-CRP and ASDAS with erythrocyte sedimentation rate (ASDAS-ESR) (beta coefficient = 1.98, p < 0.001 and beta coefficient = 1.60, p = 0.003). Firth logistic regression showed that water fraction was a significant predictor of ASDAS-CRP but not ASDAS-ESR. The intraclass correlation coefficient showed excellent repeatability for the three repeated measures of the water fraction. Conclusion: Water fraction parameter could be a good imaging biomarker of disease activity status. The sacroiliac joint evaluated by mDixon MRI may be a promising biomarker of disease progression in patients with spondyloarthritis.

Diagnostic Accuracy of Standalone T2 Dixon Sequence Compared with Conventional MRI in Sacroiliitis

Aim  The aim of this article was to assess the profile of T2-weighted (T2W) multipoint Dixon sequence and conventional sequences in magnetic resonance imaging (MRI) of sacroiliac joints for the diagnosis of active and chronic sacroiliitis.

Settings and Design  Prospective observational study.

Materials and Methods  Thirty-seven patients with sacroiliitis underwent MRI with conventional coronal oblique short tau inversion recovery, T1W sequences, and T2W multipoint Dixon sequences. T1 fat-saturated postcontrast sequences were added in active cases. Comparisons were made between conventional and T2 Dixon sequences both quantitatively and qualitatively.

Statistical Analysis  Paired t -test was used to study the difference in contrast–noise ratio (CNR) between two groups. Chi-squared analysis with p -value of ≤ 0.05 was used to test the significant association of different sequences.

Results  Water only images had highest mean CNR (296.35 ± 208.28) for the detection of bone marrow edema/osteitis. T1W (186.09 ± 96.96) and opposed-phase (OP) images (279.22 ± 188.40) had highest mean CNR for the detection of subchondral sclerosis and periarticular fat deposition, respectively. OP images ( p -value <0.001) followed by fat-only (FO) images ( p -value = 0.001) were superior to T1W sequences in detecting periarticular fat deposition. In-phase (IP) images in detecting subchondral sclerosis and IP and FO images in detecting cortical erosions were comparable to conventional T1W sequences ( p -value < 0.001).

Conclusions  T2 Dixon sequences are superior or comparable to conventional MR sequences in detection of sacroiliitis, except ankylosis. Hence, Dixon can be used as a single sequence to replace the multiple sequences used in conventional imaging protocol of acute sacroiliac joints due to higher image quality. It can be used as an additional sequence in case of chronic sacroiliitis to increase the confidence and accuracy of diagnosis.

Parallel Line Sign-A New MRI Sign Associated With Chronic Sacroiliitis: Prevalence, Characteristics, and Associations

Purpose: The purpose is to demonstrate the existence of the parallel line sign (PLS), a dark line parallel to the sacroiliac joint (SIJ), and determine its prevalence, characteristics, and associations. Methods: 200 consecutive SIJ MRIs referred by rheumatologists were retrospectively reviewed for the presence of the PLS. Presence and extent of imaging features of sacroiliitis (bone marrow edema, fatty infiltration, erosions, sclerosis, and ankylosis) were evaluated. Results: Prevalence of PLS was 11.5% (23/200), with 9 subjects having bilateral PLS, resulting in 32 SIJs showing a PLS. Every PLS involved the synovial portion of the SIJ, and almost all (31/32, 96.9%) involved the iliac (rather than sacral) side of the SIJ. Every PLS occurred with at least one established imaging feature of sacroiliitis. Presence of a PLS was associated with higher prevalence of erosions (78.3% vs 36.7% in those without PLS, P < .001), greater extent of SIJ involvement by erosions (3.6 ± 1.3 vs 2.3 ± 1.1 quadrants of the SIJ involved, P < .001), and higher density of erosions per centimeter (88.9% vs 46.2% with >2 erosions/cm, P = .001). There was higher prevalence of bone marrow edema, fatty infiltration, and sclerosis in those with PLS compared to those without PLS (P = .001, P < .001, and P = .006, respectively). Extent of involvement by any of these features was not significantly different between the two groups (P = .22, P = .16, and P = .46, respectively). Conclusions: The PLS is associated with imaging features of chronic sacroiliitis, especially erosions. Knowledge of the existence of the PLS may help avoid misdiagnosis of an insufficiency fracture and increase confidence in the diagnosis of sacroiliitis.

Multimodality Multisystem Imaging of Pregnancy-Related Changes: Featuring Neurologic, Cardiothoracic, Breast, Gynecologic, and Musculoskeletal Issues

ABSTRACT

Pregnancy and the puerperium are a time of significant physiologic change, and with an average of 4 million births in the United States yearly, radiologists encounter pregnancy-related imaging findings regularly. While many of these findings represent physiologic changes, a significant number represent pathology, making it paramount for radiologists to distinguish between the two. This case-based article reviews imaging findings within the nervous, cardiovascular, pulmonary, breast, gynecologic, musculoskeletal, digestive, hematologic, and integumentary systems throughout pregnancy and the postpartum period.

Improved Performance of Compartments in Detecting the Activity of Axial Spondyloarthritis Based on IVIM DWI with Optimized Threshold b Value

Purpose

To explore the diagnostic performance of the optimized threshold b values on IVIM to detect the activity in axial spondyloarthritis (axSpA) patients.

Method

40 axSpA patients in the active group, 144 axSpA patients in the inactive group, and 20 healthy volunteers were used to evaluate the tissue diffusion coefficient (D_slow), perfusion fraction (f), and pseudodiffusion coefficient (D_fast) with b thresholds of 10, 20, and 30 s/mm². The Kruskal-Wallis test and one way ANOVA test was used to compare the different activity among the three groups in axSpA patients, and receiver operating characteristic (ROC) curve analysis was applied to evaluate the performance for D_slow, f, and D_fast to detect the activity in axSpA patients, respectively.

Results

D_slow demonstrated a statistical difference between two groups (P < 0.05) with all threshold b values. With the threshold b value of 30 s/mm², f could discriminate the active from control groups (P < 0.05). D_slow had similar performance between the active and the inactive groups with threshold b values of 10, 20, and 30 s/mm² (AUC: 0.877, 0.882, and 0.881, respectively, all P < 0.017). Using the optimized threshold b value of 30 s/mm², f showed the best performance to separate the active from the inactive and the control groups with AUC of 0.613 and 0.738 (both P < 0.017) among all threshold b values.

Conclusion

D_slow and f exhibited increased diagnostic performance using the optimized threshold b value of 30 s/mm² compared with 10 and 20 s/mm², whereas D_fast did not.

Spondyloarthritides: Theories and beyond

Spondyloarthritides (SpA) are a family of interrelated rheumatic disorders with a typical disease onset ranging from childhood to middle age. If left untreated, they lead to a severe decrease in patients' quality of life. A succesfull treatment strategy starts with an accurate diagnosis which is achieved through careful analysis of medical symptoms. Classification criterias are used to this process and are updated on a regular basis. Although there is a lack of definite knowledge on the disease etiology of SpA, several studies have paved the way for understanding plausible risk factors and developing treatment strategies. The significant increase of HLA-B27 positivity in SpA patients makes it a strong candidate as a predisposing factor and several theories have been proposed to explain HLA-B27 driven disease progression. However, the presence of HLA-B27 negative patients underlines the presence of additional risk factors. The current treatment options for SpAs are Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), TNF inhibitors (TNFis), Disease-Modifying Anti-Rheumatic Drugs (DMARDs) and physiotherapy yet there are ongoing clinical trials. Anti IL17 drugs and targeted synthetic DMARDs such as JAK inhibitors are also emerging as treatment alternatives. This review discusses the current diagnosis criteria, treatment options and gives an overview of the previous findings and theories to clarify the possible contributors to SpA pathogenesis with a focus on Ankylosing Spondylitis (AS) and enthesitis-related arthritis (ERA).

Sacroiliac joint in sarcoidosis on computed tomography: a monocentric retrospective study (SISTER)

Sacroiliitis and spondyloarthritis (SpA) have been associated to sarcoidosis. Sarcoidosis bone involvement of the sacral or iliac bones has been reported to mimic SpA. We aimed to evaluate the prevalence of structural sacroiliitis and structural changes of the sacroiliac joints (SIJ) in patients with sarcoidosis by abdominal-pelvic computed tomography (AP-CT). In this monocentric retrospective study, three blinded readers evaluated AP-CT that had already been performed on patients with sarcoidosis and classified them as normal, degenerative, or inflammatory. A consensus was reached for the divergent cases. Erosion, ankylosis, and sclerosis, classically associated with sacroiliitis, were noted. SpA was defined according to the ASAS 2009 classification criteria. We identified 217 patients with proven sarcoidosis who underwent AP-CT. Only three patients had sacroiliitis by CT and four had SpA, representing 1.38% and 1.85% of the patients, respectively. Degenerative SIJs represented 28.1% of patients and were significantly associated with age, at least one pregnancy, rural lifestyle, ankylosis, diffuse idiopathic skeletal hyperostosis, sclerosis, and the presence of osteophytes. Four patients had axial bone sarcoidosis. Sacroiliitis, SpA, and degenerative changes of the SIJ have been highlighted by AP-CT in patients with sarcoidosis. Osteoarthritis of the SIJ in sarcoidosis was associated with age, pregnancy, and rural lifestyle. Further studies are needed to assess the link between SpA and sarcoidosis.

Task-driven assessment of experimental designs in diffusion MRI: A computational framework

This paper proposes a task-driven computational framework for assessing diffusion MRI experimental designs which, rather than relying on parameter-estimation metrics, directly measures quantitative task performance. Traditional computational experimental design (CED) methods may be ill-suited to experimental tasks, such as clinical classification, where outcome does not depend on parameter-estimation accuracy or precision alone. Current assessment metrics evaluate experiments' ability to faithfully recover microstructural parameters rather than their task performance. The method we propose addresses this shortcoming. For a given MRI experimental design (protocol, parameter-estimation method, model, etc.), experiments are simulated start-to-finish and task performance is computed from receiver operating characteristic (ROC) curves and associated summary metrics (e.g. area under the curve (AUC)). Two experiments were performed: first, a validation of the pipeline's task performance predictions against clinical results, comparing in-silico predictions to real-world ROC/AUC; and second, a demonstration of the pipeline's advantages over traditional CED approaches, using two simulated clinical classification tasks. Comparison with clinical datasets validates our method's predictions of (a) the qualitative form of ROC curves, (b) the relative task performance of different experimental designs, and (c) the absolute performance (AUC) of each experimental design. Furthermore, we show that our method outperforms traditional task-agnostic assessment methods, enabling improved, more useful experimental design. Our pipeline produces accurate, quantitative predictions of real-world task performance. Compared to current approaches, such task-driven assessment is more likely to identify experimental designs that perform well in practice. Our method is not limited to diffusion MRI; the pipeline generalises to any task-based quantitative MRI application, and provides the foundation for developing future task-driven end-to end CED frameworks.

An Omitted Radiological finding in the Pediatric Age Group: Physiological Sacroiliac Joint Vacuum Normal Variant

INTRODUCTION

Gas accumulation in human joint spaces has been generally described as the vacuum phenomenon (VP). To date, the sacroiliac joint VP has been associated mostly with pathological, particularly degenerative conditions (e.g., arthritis, obesity, discal degenerations, fractures, dislocations, avascular necrosis).

OBJECTIVE

The study aimed to examine the characteristics of the physiological form of VP and its radiological patterns in a sample of pediatric patients.

METHODS

A sample of seventy patients between 0 and 17 years old (mean age, 11.4 ± 5.54) were included in the study. Sample VP cases was evaluated according to types, age group, anatomic localization, gender, and sides. RESULTS: Two (2.9%) of sample children had degenerative VP, with 24 (34.2%) of patients demonstrating physiological VP in the sacroiliac joints. VP rates significantly increased after nine years of age (p < 0.01) and 83% of physiological VP cases were determined to be bilateral.

CONCLUSIONS

Although degenerative VP is a rare entity in children, non-pathological VP can be a more common aspect of sacroiliac anatomy. Although sacroiliac VP is frequently an underreported or omitted finding in imaging studies, this condition may be clinically important as a clue for other degenerative diagnoses. Normal variants of VP may be clinically important in children since they may mimic inflammatory and infectious pathologies during magnetic resonance imaging and computed tomography images.

Role of diagnostic imaging in psoriatic arthritis: how, when, and why

Psoriasis is a common skin disease. Up to 30% of patients with psoriasis develop psoriatic arthritis (PsA) resulting, by far, the most prevalent coexisting condition. Heterogeneity of clinical and radiological presentation is a major challenge to diagnosis of PsA. Initial reports about PsA emphasized a benign course in most patients, but it is now recognized that psoriatic arthritis often leads to impaired function and a reduced quality of life. PsA is a progressive disease characterized by diverse clinical features, often resulting in diagnostic delay and treatment that are associated with poor clinical and structural outcomes. New effective treatments may halt PsA progression, and consequently, treatment goals have evolved from simple reduction of pain to achieving full remission or minimal disease activity. This emerging treat-to-target strategy paradigm emphasize a need for early diagnosis; sensitive imaging techniques may be of value in this process. While radiography and CT depict structural damage, US and MRI have emerged as helpful tools to evaluate magnitude and severity of active inflammatory lesions. This review aims to describe the role of imaging modalities in diagnosis, follow-up and prognosis of PsA.

Subclinical sacroiliitis detected by abdominopelvic computed tomography in Korean patients with Crohn's disease

BACKGROUND/AIMS

Sacroiliitis is a frequent extraintestinal manifestation of inflammatory bowel diseases (IBDs). This study aimed to assess the prevalence of sacroiliitis using a validated screening tool based on abdominopelvic computed tomography (APCT) in Korean patients with Crohn's disease (CD) and examine potential associations between clinical characteristics and sacroiliitis.

METHODS

One hundred five patients with CD undergoing APCT for any indication at an IBD clinic were matched 1:1 for age and sex with 105 controls without underlying chronic illnesses. Using a validated APCT screening tool that defines sacroiliitis as either ankylosis or a total erosion score (TES) ≥ 3, all computed tomography scans were assessed by two independent, blinded radiologists. We compared the prevalence of sacroiliitis between CD patients and controls and clinical characteristics between CD patients with and without sacroiliitis.

RESULTS

The prevalence of sacroiliitis was significantly higher in CD patients than in controls (13.3% vs. 4.8%, p = 0.030). All subjects with sacroiliitis had a TES ≥ 3, but no ankylosis. The assessment of sacroiliitis in APCT showed excellent interreader reliability (Cohen's kappa = 0.933 for presence of sacroiliitis). Sacroiliitis in CD patients was bilateral and asymptomatic. There were no significant associations between sacroiliitis and any demographic data or clinical characteristics in these patients.

CONCLUSION

The prevalence of APCT-detected sacroiliitis in CD patients was higher than that in controls, but the condition was asymptomatic. The clinical significance of asymptomatic sacroiliitis in Korean CD patients remains unclear.

Radiologic Mimics of Osteomyelitis and Septic Arthritis: A Pictorial Essay

Various imaging techniques may be employed in the investigation of suspected bone and joint infections. These include ultrasound, radiography, functional imaging such as positron emission tomography (PET) and nuclear scintigraphy, and cross-sectional imaging, including computed tomography (CT) and magnetic resonance imaging (MRI). The cross-sectional modalities represent the imaging workhorse in routine practice. The role of imaging also extends to include assessment of the anatomical extent of infection, potentially associated complications, and treatment response. The imaging appearances of bone and joint infections are heterogeneous and depend on the duration of infection, an individual patient's immune status, and virulence of culprit organisms. To add to the complexity of radiodiagnosis, one of the pitfalls of imaging musculoskeletal infection is the presence of other conditions that can share overlapping imaging features. This includes osteoarthritis, vasculopathy, inflammatory, and even neoplastic processes. Different pathologies may also coexist, for example, diabetic neuropathy and osteomyelitis. This pictorial review aims to highlight potential mimics of osteomyelitis and septic arthritis that are regularly encountered, with emphasis on specific imaging features that may aid the radiologist and clinician in distinguishing an infective from a noninfective aetiology.

Review of Current Evidence for Minimally Invasive Posterior Sacroiliac Joint Fusion

The sacroiliac joint (SIJ) is a large, irregularly shaped, serpentine joint structure bordered anteriorly and posteriorly by the sacroiliac ligaments. With increased recognition of the SIJ as a pain source, treatments have been historically nonsurgical in nature. Common treatments include bracing, medications, activity modification, manual therapy, chiropractic manipulation, physical therapy, and intra-articular SIJ injections. Surgical stabilization and/or fusion of the SIJ may be considered when a patient has persistent moderate to severe pain, functional impairment, and failed conservative management. Surgical stabilization and fusion has traditionally been by way of the transiliac approach. More recent SIJ fusion systems have proposed not only a posterior approach but one that stabilizes the joint space by placing an allograft within the SIJ. Anatomically, a posterior approach is able to avoid neurovascular structures that otherwise are encountered with the transiliac approach and may be performed percutaneously. Preliminary evidence reports consistent pain reduction with minimal complications. This paper is purposed to detail the present evidence of minimally invasive posterior SIJ fusion, as well as highlight the need for further research moving forward.

A Review and Algorithm in the Diagnosis and Treatment of Sacroiliac Joint Pain

INTRODUCTION

The sacroiliac joint (SIJ) has been estimated to contribute to pain in as much as 38% of cases of lower back pain. There are no clear diagnostic or treatment pathways. This article seeks to establish a clearer pathway and algorithm for treating patients.

METHODS

The literature was reviewed in order to review the biomechanics, as well as establish the various diagnostic and treatment options. Diagnostic factors addressed include etiology, history, physical exam, and imaging studies. Treatment options reviewed include conservative measures, as well as interventional and surgical options.

RESULTS

Proposed criteria for diagnosis of sacroiliac joint dysfunction can include pain in the area of the sacroiliac joint, reproducible pain with provocative maneuvers, and pain relief with a local anesthetic injection into the SIJ. Conventional non-surgical therapies such as medications, physical therapy, radiofrequency denervation, and direct SI joint injections may have some limited durability in therapeutic benefit. Surgical fixation can be by a lateral or posterior/posterior oblique approach with the literature supporting minimally invasive options for improving pain and function and maintaining a low adverse event profile.

CONCLUSION

SIJ pain is felt to be an underdiagnosed and undertreated element of LBP. There is an emerging disconnect between the growing incidence of diagnosed SI pathology and underwhelming treatment efficacy of medical treatment. This has led to an increase in SI joint fixation. We have created a clearer diagnostic and treatment pathway to establish an algorithm for patients that can include conservative measures and interventional techniques once the diagnosis is identified.

The role of radiography in the study of spinal disorders

Despite the growing use of computed tomography (CT) and magnetic resonance imaging (MRI) in the study of spinal disorders, radiography still plays an important role in many conditions affecting the spine. However, the study and interpretation of spine radiograph is receiving less attention and radiologists are increasingly unfamiliar with the typical findings in normal and pathologic conditions of the spine. The aim of this article is to review the radiologic indications of radiograph in different pathologic conditions that affect the spine, including congenital, traumatic, degenerative, inflammatory, infectious and tumour disorders, as well as their main radiographic manifestations.

Ultrasound as a Biomarker in Rheumatic Diseases

Rheumatic diseases are a heterogeneous group of disorders which often affect the musculoskeletal system. Given the lack of definitive testing, there are limited diagnostic tools at clinicians’ disposal. Over the recent decades, ultrasonography has gained widespread use within rheumatology due to its accessibility, safety, and relatively low cost. This review describes the clinical utility of ultrasound as a biomarker in the diagnosis and management of several rheumatic diseases.

Ectopic bone formation and systemic bone loss in a transmembrane TNF-driven model of human spondyloarthritis

BACKGROUND

The transmembrane-TNF transgenic mouse, TgA86, has been shown to develop spontaneously peripheral arthritis with signs of axial involvement. To assess similarity to human spondyloarthritis, we performed detailed characterization of the axial, peripheral, and comorbid pathologies of this model.

METHODS

TgA86 bone pathologies were assessed at different ages using CT imaging of the spine, tail vertebrae, and hind limbs and characterized in detail by histopathological and immunohistochemical analysis. Cardiac function was examined by echocardiography and electrocardiography and bone structural parameters by μCT analysis. The response of TgA86 mice to either early or late anti-TNF treatment was evaluated clinically, histopathologically, and by μCT analysis.

RESULTS

TgA86 mice developed with 100% penetrance spontaneous axial and peripheral pathology which progressed with time and manifested as reduced body weight and body length, kyphosis, tail bendings, as well as swollen and distorted hind joints. Whole-body CT analysis at advanced ages revealed bone erosions of sacral and caudal vertebrae as well as of sacroiliac joints and hind limbs and, also, new ectopic bone formation and eventually vertebral fusion. The pathology of these mice highly resembled that of SpA patients, as it evolved through an early inflammatory phase, evident as enthesitis and synovitis in the affected joints, characterized by mesenchymal cell accumulation, and neutrophilic infiltration. Subsequently, regression of inflammation was accompanied by ectopic bone formation, leading to ankylosis. In addition, both systemic bone loss and comorbid heart valve pathology were evident. Importantly, early anti-TNF treatment, similar to clinical treatment protocols, significantly reduced the inflammatory phase of both the axial and peripheral pathology of TgA86 mice.

CONCLUSIONS

The TgA86 mice develop a spontaneous peripheral and axial biphasic pathology accompanied by comorbid heart valvular dysfunction and osteoporosis, overall reproducing the progression of pathognomonic features of human spondyloarthritis. Therefore, the TgA86 mouse represents a valuable model for deciphering the role of transmembrane TNF in the pathogenic mechanisms of spondyloarthritis and for assessing the efficacy of human therapeutics targeting different phases of the disease.