Imaging in Spondyloarthritis Diagnosis

Introduction

Spondyloarthritis is a group of medical conditions with similar genetic, clinical and laboratory features. The most significant similarity between the group is that all the diseases are associated with HLA-B27, which is a human leukocyte antigen (Reveille 1998). However, among the Spondyloarthritis is a prototypic disease called Ankylosing spondylitis, usually characterized by axial skeletal. Other members of the Spondyloarthritis group include inflammatory bowel arthritis, psoriatic arthritis HLA-B27 related uveitis, as well as other undifferentiated forms (Paparo, et al. 2014). While this group of diseases usually have peripheral articular involvement, an axial skeleton is also often seen. This essay seeks to identify and review literature about the role of imaging on the diagnosis and assessment of Seronegative Spondyloarthropathy (Spondyloarthritis). The review will include research evidence drawn from different journal articles selected from online databases such as EBSCO, PUBMED and ProQuest.

The improvement in imaging technology and further research has contributed to a better diagnosis of Spondyloarthritis in the last few decades. Better diagnosis has also contributed to the development and assessment of treatment interventions (Dougados, 2011). Nonetheless, until recently, the diagnosis and assessment of Spondyloarthritis relied on conventional radiography albeit radiographic changes developing at least five years after the onset of symptoms (Char-Valckenaere et al 2011, Guglielmi et al 2011).

Research by Spondyloarthritis International Society (ASAS) has developed a diagnosis guideline for Spondyloarthritis especially for younger people (i.e. age 45 and below) who have had lower back pains for at least 3 months. The diagnostic criteria state that Spondyloarthritis is present if the conventional radiography or MRI shows sacroiliitis together with either HLA-B27 or if one of them is present together with other clinical findings. The clinical findings may be a positive response to nonsteroidal anti-inflammatory drugs, family history of spondyloarthropathy, psoriasis, uveitis, or inflammatory back pain. According to Rudwaleit et al (2004), the MRI of the sacroiliac joint is included in the diagnostic criteria because MRI is one of the most effective methods of identifying inflammations thereby enabling early patient diagnosis using normal radiographic findings. Consequently, early therapeutic intervention is taken to save lives and improve the patient’s well-being.

While Rudwaleit et al (2004) estimate that this group of disorders has an estimated MIR sensitivity and specificity of 90%, the sensitivity can be higher with correct image interpretation by a qualified musculoskeletal radiologist with significant experience in rheumatologic diseases (Rudwaleit et al, 2005). Nonetheless, van den Berg & van der Heijde (2010) note that for axial spondyloarthritis to be diagnosed based on the ASAS criteria, the MRI of sacroiliitis and at least one of the clinical features must have a 97.2% and 94.2% sensitivity and specificity respectively. Here, we will identify how imaging plays an important role in identifying the pathophysiologic and clinical feature of the disease. Furthermore, there will be a discussion on the role of imaging in revealing the differential diagnosis of Seronegative Spondyloarthropathy based on the ASAS guidelines.

Role of imaging in clinical and pathophysiology findings

Bollow et al (2002) argue that MIR is one of the most effective methods of detecting the sacroiliac joints and spine inflammatory changes due to its sensitivity. The popularity for the MRI technique has been on the rise particularly in monitoring therapeutic response as well as disease activity. In this regard, ASAS has developed a guideline for identifying the existence of chronic and inflammatory lesions in the sacroiliac joints and spine (Van der Linden et al 2005, Sieper et al, 2009).

Identifying active inflammatory lesions in the Sacroiliac joints

Bone marrow edema

It is not until an MRI is performed that a bone marrow edema can be identified. According to Sieper et al (2009), the STIR images signifying bone marrow edema have a high signal intensity as well as suppressed contrast-enhanced T1-weighted images. Bone marrow edema is located on subchondral bone surfaces or periarticular on the sacroiliac joints. When the edema appears to be unilateral, the diagnosis must exclude infectious sacroiliitis. Nonetheless, according to Landew et al (2005), disease activity is likely to be noted when the imaging reveals stronger signal hypersensitivity. Imaging might also reveal certain structural changes such as erosions, which are also associated with bone marrow edema (Sieper et al, 2009). However, Braun et al (2007) & Landew et al (2005) observe that when identifying inflammatory lesions, the unilateral and asymmetric sacroiliac joint involvement does not indicate the presence of ankylosing spondylitis but rather suggests the existence of other types of spondyloarthritis such as psoriatic arthritis.

Synovitis and capsulitis

Through MIR, radiologists can detect Synovitis and capsulitis that are identified by the high signal intensity in the anterior and posterior or synovial capsules of the sacroiliac joints. This is evident on fat-suppressed contrast-enhanced T1-weighted images of MRI. However, according to Taylor and Robinson (2013), STIR images cannot be used to differentiate joint fluid and synovitis and therefore radiologists can administer gadolinium for easier differentiation.

Enthesitis

To identify Enthesitis, MRI images must have high signal intensity at the joint between tendons and ligaments, tendons, capsules or fascia on STIR images and fat-compressed contrast-enhanced T1-weighted images. The adjacent bone marrow, as well as surrounding soft tissue, may also have high signal intensity. Here, it is the role of a radiologist to identify that the vessel-surrounded ligaments, as well as some coil, artefacts may appear as inflammatory lesions that resemble enthesis (Taylor and Robinson 2013).

Identifying Chronic Inflammatory Lesions in the Sacroiliac Joints

Erosions

The MRI can identify bony defects (Erosions) on the surface of the joint by seeing low signal intensity on T1-weighted images (Lacout, Rousselin and Pelage 2008). The defects may also appear on the joint’s cartilaginous compartment. Using MRI, the examiner may identify erosions that initially appear as single lesions that may subsequently cause a false sacroiliac joint enlargement upon becoming confluent.

Subchondral sclerosis

MRI can also be used to detect Subchondral sclerosis. According to Lacout, Rousselin and Pelage (2008), Subchondral sclerosis appears on both sacral and iliac surfaces of the joint in a low signal on STIR and T1-weighted images and do not enhance on fat-suppressed contrast-enhanced T1-weighted images. The MRI may also reveal Subchondral sclerosis to have extended at least 5 mm from the joint surface.

Fat depositions

MRI can also be used to identify Fat depositions. Here, the radiologist identifies depositions of bone fat by an increased signal intensity in periarticular bone marrow on T1-weighted images. However, this finding is not specific and may be indicative of previously inflamed areas on spondyloarthritis patient.

Ankylosis

Ankylosis refers to the combination of bone surfaces across a joint and are usually characterized by low signal intensity when subjected to all sequences of MRI. Similar signal intensity is observable in the next adjacent bone marrows and is often characterized by areas of fatty degeneration of high signal intensity on T1-weighted images (Lacout, Rousselin and Pelage 2008).

Use of MRI in the Identification of active inflammatory lesions in the spine

MRI is also useful in identifying active inflammatory lesions in the spine such as Spondylodiskitis, Costovertebral arthritis, Facet joint arthritis and Enthesitis of spinal ligaments.

Spondylodiskitis

Also known as inflammatory Andersson lesions, Spondylodiskitis can be identified by MRI because of its cortical plates adjacent to intervertebral discs reveal a high signal intensity on STIR images and fat-suppressed contrast-enhanced T1-weighted images (Sieper et al, 2009). The high signal intensity might also be seen at the center all over the intervertebral space resembling inflammatory diskitis. According to Sieper et al (2009), MRI can also identify Andersson lesions in a percentage (33%) of patients with spondyloarthritis; and this group of diseases has a specificity of 59%.

Spondylitis

Spondylitis exists in the anterior or posterior vertebral’s bone marrow and can be identified when the STIR images have a high signal intensity as well as on fat-suppressed contrast-enhanced T1-weighted images (Colbert 2010). Radiographically, anterior Spondylitis is equivalent to a Romanus lesion (Sieper et al, 2009) as highlighted in figure 5B and 5A. They are observable in 67% of spondyloarthritis patients (Bennet et al, 2009) and when there are three corners in the absence of schmorl or osteophytes, its specificity is 81%. However, according to Hermann et al (2004) & Braun et al (2007), the specificity might increase to 97% in patients below the age of 40 years.

Often, MRI reveals well-defined ankylosing spondylitis lesions. On the other hand, according to (Hermann et al 2004 & Braun et al 2007) diffuse and extensive vertebral involvement usually indicates the existence of other types of spondyloarthritis especially because this sub-group of disease does have non-ascending vertebral involvement (Hermann et al 2004).

Facet joint arthritis

MRI can also facilitate the identification of the facet joints situated between C2 and S1 in spondyloarthritis patients and is often associated with bone marrow edema found in spinal pedicles

Use of imaging in the Identification of chronic inflammatory lesions of the spine

Evidence by ASA indicates that radiography is the most effective method to identify chronic changes and can be used to care for patients with an established illness (Sieper et al, 2007). On the contrary, according to Sieper et al (2007) radiography is not an effective method of conducting an early spondyloarthritis diagnosis because of its inability to depict inflammations. However, MRI can be used for the same purpose because depicts inflammations. On the other hand, Sieper et al (2007) acknowledge that CT has better capabilities of depicting chronic bony changes compared to radiography although it is rarely used due to its radiation exposure.

In the case of ankylosis and Syndesmophytes, MRI can be used to detect new bine formations at the vertebral body corners of the patient has a long-standing disease. The MRI identifies it as a vertically oriented and thin bone formation within disks’ peripheries. They are areas of new bone formation that are mostly bilaterally or symmetrically structured as illustrated in figure 3A. MRI might also reveal areas of new bone formation that are thick and irregular whose vertebral corners have large implantation bases and are mostly regarded as pseudosyndesnophytes and are usually never related to ankylosing spondylitis. They suggest other forms of spondyloarthritis such as psoriatic arthritis (Herman et al, 2004).

MRI can also help in the diagnosis of Ankylosis, which are new bone formation and bony bridges that occur in the intervertebral disks in a long-standing illness. They present in low signal intensity in all MRI (e.g. figure 3C) and the adjacent bone marrow may display the same signal intensity displayed in the sacroiliac joint and may sometimes be surrounded by areas of fatty replacement with high signal intensity on T1-weighted images (Paparo, et al. 2014).

Lastly in this category, MRI can identify Fat deposition on vertebral corners, which are bine fat deposits that can best be seen when on T1-weighed images. The availability of these bone fat deposits indicates the presence of previous inflammations and are good predictors of new syndesmophytes formations. The study results by Bennett et al (2010) suggest that a positive spondyloarthritis diagnosis may be supported by the availability of more than five of these lesions.

Discussion

The findings of this review indicate the exitance of a positive relationship between the imaging findings and the existence of Seronegative Spondyloarthropathy symptoms. However, these findings are based on studies with specific methodological weaknesses that affect the generalizability of the findings. However, there are several implications of these findings to practice that are worth mentioning. For instance, when choosing the studies to be included in the review, studies with a minimum of 20 subjects were favored particularly because smaller sample populations often affect diagnostic accuracy (Paparo, et al. 2014). Meanwhile, future studies should include wider population samples to improve the accuracy and credibility of the evidence.

The sampling methods in most of the reviewed studies were either not well described of insufficient and this makes it difficult to eliminate the possibility of selection bias. When conducting studies of diagnostic nature, it is important to ensure diagnostic accuracy by effectively elaborating the study sample as well as the sampling strategy. For instance, it is important to highlight whether the sample population was unselectively and systematically selected and in the context of case-control studies, it is important to mention whether the two study groups were comparable or not. Moreover, some of the articles reviewed in this study seem to have underestimated the importance of control groups even though the description and sampling of the control group participants are as important as the description and sampling of the intervention group.

The fact that there is no gold standard for the diagnosis of Seronegative Spondyloarthropathy which is rather based on a composite of clinical presentations undermines the evaluation of MRI as a diagnostic approach. However, researchers (Taylor and Robinson 2013) agree that when assessing a diagnostic test, it is essential t have a reference standard. Thus, when using MRI are used to make a Seronegative Spondyloarthropathy diagnosis as evident in more than half of the reviewed studies, bias is highly likely to occur. Ideally, popular use of MRI as the diagnosis for Seronegative Spondyloarthropathy limits the possibilities of engaging in more meaningful studies on the accuracy of MRI as a diagnostic tool.

A possible strategy that could be explored to improve the reliability of MRI as a diagnostic tool for Seronegative Spondyloarthropathy is to test whether the selected standards of references can be reproduced. However, none of the reviewed articles has tested that reproducibility. Similarly, the reliability of MRI diagnosis would be strengthened by including a longitudinal aspect to the studies while following up on advanced stages of the disease to confirm the diagnosis.

While there are several activity scores have been developed for structural and inflammatory MRI currently exist, scientists all over the world still lack a consensus on how to define diagnostic MRI findings. However, all the reviewed studies generally defined the MRI findings despite little homogeneity between these definitions. Meanwhile, according to Bennet et al (2009), it is important to define MRI findings before testing its diagnostic utility. The test protocol should also be conducted by a qualified musculoskeletal radiologist.

Application of the findings

The review has identified many academic papers have a positive view of the importance of MRI in the diagnosis of Seronegative Spondyloarthropathy. The positive perception of MRI as a diagnostic tool for Seronegative Spondyloarthropathy largely emanates from the obvious need to optimize the diagnostic process of Seronegative Spondyloarthropathy. Furthermore, the fact that the new ASAS diagnostic criteria include MRI as one of the diagnostic tools has boosted practitioners’ confidence in MRI. However, with regards to the current review, there is a paucity of high-quality research on the use of MRI as a diagnostic tool for Seronegative Spondyloarthropathy and thus MRI should still not be considered a gold standard for Seronegative Spondyloarthropathy diagnosis until further and more research is conducted on this area. This is because there is a risk of Seronegative Spondyloarthropathy being misdiagnosed if structural and inflammatory findings fare interpreted as being more specific than they are.

Limitations and strengths of the review

The strength of this review is the rigorous assessment of studies included. During the search process, the researcher evaluated the quality of each literature material using the Critical Appraisal Skills framework, that not only examined the methodological rigour of each study but also the applicability of their findings to local practice. However, the limitations of this review are the lack of space to give further detail on the study selection criteria and the use of a limited number of databases to do the literature search.

References

Rudwaleit M, van der Heijde D, Khan MA, et al. How to diagnose axial spondyloarthritis early.

Van der Linden S, Van der Heijde D, Braun J. Ankylosing spondylitis. In: , Harris ED, Budd RC, Firestein GS, et al, eds. Kelley???s textbook of rheumatology, 7th ed, vol 2. Philadelphia, PA: Elsevier Saunders, 2005:1125-1141

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