Magnetic resonance imaging of active sacroiliitis: Do we really need gadolinium?
Introduction
Sacroiliitis is the hallmark of spondyloarthritis. The term spondyloarthritis encompasses a heterogeneous group of diseases of which ankylosing spondylitis (AS) is the main representative. Other members of this disease group are psoriatic arthritis (PsA), reactive arthritis (ReA), arthritis in inflammatory bowel disease (IBD), and undifferentiated spondyloarthritis (USpA) [1]. The leading symptom of sacroiliitis is inflammatory back pain [2]. The diagnosis of ankylosing spondylitis is still based on the demonstration of structural changes (erosions, para-articular sclerosis, and ankylosis) by conventional radiographs although magnetic resonance imaging (MRI) can demonstrate inflammatory changes of the sacroiliac joints several years earlier [3]. The MRI diagnosis is based on the demonstration of both structural and active changes. Structural changes are identified using unenhanced T1-weighted fast spin-echo sequences, which may be supplemented by a T2-weighted gradient-echo sequence or a fat-saturated T1-weighted sequence. Active inflammatory changes of the sacroiliac joints comprise para-articular bone marrow edema, intra-articular synovitis, and surrounding enthesitis or capsulitis and can be demonstrated by three MRI techniques: short tau inversion recovery (STIR) sequence, fat-saturated T2-weighted fast spin-echo sequences, and fat-saturated T1-weighted fast spin-echo sequences after administration of gadolinium-based contrast medium (T1/Gd). The first two sequences are comparable in terms of image contrast and spatial resolution and depict active inflammatory lesions in sacroiliitis as increased signal intensity due to the presence of increased amounts of free water and their T2 effects. Contrast-enhanced, fat-saturated T1-weighted sequences, on the other hand, depict areas of increased vascularization due to increased diffusion of gadolinium–DTPA into the interstitial space and its T1-shortening effect. Good agreement between STIR and T1/Gd sequences was found in follow-up studies of active spinal changes in ankylosing spondylitis in patients treated with tumor necrosis factor-(TNF-)alpha antagonists [4], [5]. Similar scientific evidence for the diagnostic benefits of contrast-enhanced imaging in sacroiliitis is still lacking. Current protocol recommendations for MRI of the sacroiliac joints are based on expert opinions.
The aim of the present study was to investigate whether postcontrast imaging after administration of paramagnetic contrast material yields significant additional information and improves accuracy in diagnosing sacroiliitis.
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Materials and methods
This retrospective study included 105 patients (46 men and 59 women; mean age: 44 years), who were referred to our department for suspected sacroiliitis by the rheumatology outpatient service of our university hospital. The study was approved by the local ethics committee.
Descriptive statistics
Among the 105 patients included in the study, 59% were HLA-B27 positive and 58% had inflammatory back pain. The patients had a mean CRP of 7.1 mg/dl and a clinical activity index of 5.1 (Bath Ankylosing Spondylitis Disease Activity Index, BASDAI) [7].
In the further clinical course, 72 of the 105 patients (68%) were diagnosed with a spondyloarthritis. In this subset, 70% were positive for HLA-B27 and 69% had inflammatory back pain. Twenty-eight patients were diagnosed with AS, 6 with PsA, one
Discussion
The study presented here was conducted to evaluate the role of contrast medium administration for MR imaging of active sacroiliitis by directly comparing the two most widely used pulse sequences for this indication, namely STIR and contrast-enhanced T1-weighted fat-saturated sequences. MRI is evolving into the gold standard for imaging of sacroiliitis [8], [9]. TNF-alpha blockers have the potential to improve outcome, and this new therapeutic option has markedly increased the demand for MRI
Conclusion
STIR sequences alone are sufficient for establishing a reliable diagnosis and quantify the amount of inflammation in active sacroiliitis. A contrast-enhanced study is dispensable in the setting of clinical follow-up studies or in patients with established disease. However, a contrast-enhanced MR sequence is beneficial to ensure maximum diagnostic confidence when patients with early sacroiliitis are examined. The H/B sacroiliitis score proved useful and reliable.
Conflicts of interest
There is no conflict of interest.
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